How Electrical Troubleshooting Identifies Hidden HVAC Issues

duct cleaning

The world of HVAC systems is like a finely tuned symphony, with each component playing its part in creating a harmonious environment within our homes and workplaces. However, beneath the surface of these complex systems lurk hidden issues that can disrupt their performance and efficiency. Identifying these hidden problems is crucial for maintaining the system's longevity and ensuring comfort. Preventing costly breakdowns starts with Energy efficient cooling solutions proper maintenance can help lower energy costs.. One of the most effective techniques for uncovering these concealed issues is electrical troubleshooting.


Electrical troubleshooting serves as an investigative tool, allowing technicians to delve into the intricate network of wires, circuits, and components that make up an HVAC system. It involves a methodical process of diagnosing electrical faults that may not be immediately visible but have significant implications on the system's functionality. By focusing on electrical aspects, technicians can pinpoint anomalies such as voltage imbalances, faulty wiring, or malfunctioning sensors-factors that might otherwise remain undetected until they cause more severe problems.


The importance of identifying hidden HVAC issues through electrical troubleshooting cannot be overstated. A seemingly minor electrical fault can lead to inefficiencies that increase energy consumption and elevate utility bills. For instance, a malfunctioning thermostat sensor may cause inconsistent temperature regulation, forcing the system to work harder than necessary. Similarly, unnoticed wiring problems could lead to intermittent operation or even complete system failure.


Moreover, addressing these hidden issues proactively enhances safety. Electrical faults pose significant risks such as overheating or short circuits that could potentially lead to fires if left unaddressed. Regular electrical inspections help mitigate these dangers by ensuring all components are functioning correctly and safely.


In addition to safety and efficiency concerns, uncovering hidden HVAC issues early also contributes to cost savings in the long run. Repairing small electrical faults promptly is generally less expensive than dealing with major breakdowns or replacing entire components due to prolonged neglect. This proactive approach extends the lifespan of HVAC systems and reduces downtime.


Furthermore, identifying hidden HVAC issues through electrical troubleshooting facilitates better indoor air quality and comfort levels. When all parts function optimally without underlying disruptions, it ensures consistent airflow distribution and accurate temperature control-essential elements for creating a comfortable living or working environment.


In conclusion, while HVAC systems might appear robust on the outside, it's essential not to overlook potential internal flaws lurking beneath their surface. Electrical troubleshooting acts as both a detective and guardian against these hidden threats by revealing them before they escalate into larger problems. Through this meticulous process of identification and resolution, we safeguard our comfort zones while optimizing energy use-and ultimately paving the way for sustainable living environments well into the future.

Importance of Identifying Hidden HVAC Issues

Common Electrical Problems Affecting Air Conditioning Performance

Air conditioning systems are vital for maintaining comfort in homes and businesses, especially during the sweltering heat of summer. However, like all complex machinery, these systems can suffer from a range of problems that impact their performance. While some issues are mechanical or refrigerant-based, electrical problems often lie at the heart of poor air conditioning performance. Understanding these common electrical issues and how they can be identified through troubleshooting is crucial for ensuring efficient HVAC operation.


One of the most prevalent electrical problems affecting air conditioning systems is faulty wiring. Over time, wires can become frayed or corroded due to exposure to the elements or improper installation practices. This deterioration can lead to short circuits, power surges, or even complete system failure. Additionally, loose connections within the wiring network can cause intermittent power losses that disrupt the consistent performance of an air conditioning unit.


Another common issue is related to capacitors and relays within the HVAC system. Capacitors are responsible for providing the initial jolt of electricity needed to start up compressors and fan motors.

How Electrical Troubleshooting Identifies Hidden HVAC Issues - duct cleaning

  1. heat exchanger inspection
  2. blower fan replacement
  3. commercial HVAC services
If a capacitor fails or weakens over time, it can lead to sluggish start-ups or prevent the AC from functioning altogether. Similarly, relays act as switches that control various components within the unit; if a relay becomes stuck open or closed due to electrical faults, it can result in continuous running or failure to engage necessary parts.


Thermostat malfunctions also fall under typical electrical problems that affect AC performance. A thermostat governs when your air conditioner turns on and off based on temperature settings. If there's an issue with its wiring or sensors malfunctioning due to electrical glitches, it may not communicate accurately with your AC unit. This miscommunication results in inefficient cooling cycles and inconsistent indoor temperatures.


Electrical troubleshooting plays a pivotal role in identifying these hidden HVAC issues before they escalate into more severe problems. By using multimeters and other diagnostic tools, technicians can test voltage levels across different components to detect anomalies indicative of underlying electrical faults. For instance, measuring voltage drop across capacitors helps determine their health status while continuity tests on wires reveal breaks in connections that need addressing.


Furthermore, regular maintenance checks often include inspecting circuit boards for signs of damage such as burnt traces which might indicate overheating problems stemming from excessive current draw by malfunctioning parts elsewhere in the system.


In conclusion, while many people focus primarily on mechanical aspects when considering air conditioning inefficiencies-such as clogged filters or refrigerant leaks-it's essential not to overlook potential electrical troubles lurking beneath those symptoms' surface layers too! Addressing these underlying causes through thorough troubleshooting ensures optimal cooling efficiency extends equipment lifespan significantly reduces unexpected breakdowns during peak usage periods keeping environments comfortably cool without interruption throughout hot summer months ahead!

Tools and Techniques for Effective Troubleshooting

Electrical troubleshooting is an essential skill for HVAC technicians, as it involves diagnosing and resolving issues that may not always be immediately visible. In the realm of heating, ventilation, and air conditioning systems, electrical problems can often manifest as hidden issues, lurking beneath the surface until they cause significant disruptions. To effectively identify these hidden problems, technicians rely on a combination of tools and techniques that enable them to pinpoint issues with precision and efficiency.


One of the fundamental tools in electrical troubleshooting is the multimeter. This versatile device allows technicians to measure voltage, current, and resistance within an HVAC system. By using a multimeter to check circuit continuity and verify power supply levels, technicians can quickly identify if an electrical component is malfunctioning or if there are problems within the wiring itself. This step is crucial in determining whether the issue lies in a specific part or if it's part of a larger systemic problem.




How Electrical Troubleshooting Identifies Hidden HVAC Issues - radiant heating systems

  1. duct cleaning
  2. radiant heating systems
  3. smart thermostat installation

Another valuable tool is the infrared thermometer or thermal imaging camera. These devices help detect temperature discrepancies in electrical components and connections that could indicate underlying issues such as overheating or poor insulation. By visualizing heat patterns, technicians can identify areas where energy loss occurs or where components are operating outside their optimal temperature range. This technique provides insight into potential failures before they become critical.


In addition to these tools, effective troubleshooting relies heavily on systematic approaches and analytical thinking. Technicians must follow structured methods such as checking power supplies first before moving on to more complex diagnostics. They need to understand schematics and wiring diagrams thoroughly to trace circuits accurately and identify possible points of failure.


Furthermore, comprehensive knowledge of common HVAC system faults plays a pivotal role in effective troubleshooting. Technicians should be familiar with symptoms related to faulty capacitors, relays, thermostats, motors, and other key components so they can quickly correlate observed problems with potential causes.


Communication skills also play an integral role in this process; understanding client descriptions of symptoms helps guide initial investigations while keeping clients informed about findings builds trust throughout repairs.


Ultimately though technology has advanced greatly providing sophisticated diagnostic tools like automated service apps integrated into newer HVAC systems-human expertise remains irreplaceable when dealing with complex interactions between mechanical parts & electronic controls found within modern units today .Therefore mastering both technical proficiency along interpersonal abilities ensures successful identification resolution even those most elusive hidden electrical challenges encountered during routine maintenance tasks!

Tools and Techniques for Effective Troubleshooting

Step-by-Step Process for Diagnosing Electrical Issues in Air Conditioners

Diagnosing electrical issues in air conditioners can be a perplexing task, yet it is an essential step in ensuring the efficient and reliable operation of HVAC systems. The process of electrical troubleshooting acts as a detective's magnifying glass, revealing hidden problems that could otherwise lead to serious malfunctions or even complete system failures. A systematic approach to diagnosing these issues not only saves time and resources but also enhances safety and prolongs the lifespan of the equipment.


The first step in this methodical process is to gather information about the air conditioner's symptoms. This involves speaking with the unit's users to understand what anomalies have been observed—such as unusual noises, irregular cooling patterns, or frequent tripping of circuit breakers. This preliminary step sets the stage for more detailed investigation by narrowing down potential problem areas.


Next, it's crucial to perform a visual inspection of the HVAC system. This includes checking for loose connections, signs of overheating like discolored wires or melted insulation, and any visible damage to components such as capacitors or contactors. Such an inspection can often reveal glaring issues that may have been overlooked.


Following this, one must proceed with testing the electrical components using appropriate tools like multimeters and ammeters. Testing should begin at the power source and follow through to individual components such as thermostats, compressors, fans, and transformers. By measuring voltage levels and current flow at various points in the system, technicians can identify discrepancies that indicate faulty components or wiring issues.


A critical part of this diagnostic journey involves understanding schematics and electrical diagrams specific to the air conditioning unit being examined. These diagrams serve as blueprints for tracing circuits and verifying that connections are configured correctly according to manufacturer specifications.


Once potential faults are identified through testing and analysis, repairs can be undertaken. It may involve replacing defective parts like fuses or relays or correcting wiring inconsistencies. Post-repair verification is vital; technicians should re-test all affected circuits to ensure that repairs have resolved the initial problems without introducing new ones.


In conclusion, diagnosing electrical issues in air conditioners demands a disciplined approach characterized by careful observation, systematic testing, and thorough comprehension of technical schematics. This step-by-step process not only uncovers hidden problems lurking within HVAC systems but also reinforces preventive maintenance practices that can avert future breakdowns. Ultimately, by honing their troubleshooting skills, HVAC professionals can provide enhanced service reliability while safeguarding both equipment longevity and user comfort.

Case Studies: Real-World Examples of Hidden HVAC Problems Uncovered through Electrical Troubleshooting

Title: Case Studies: Real-World Examples of Hidden HVAC Problems Uncovered through Electrical Troubleshooting


In the world of facility management and building maintenance, Heating, Ventilation, and Air Conditioning (HVAC) systems play a pivotal role in ensuring comfort and air quality. However, these complex systems are prone to hidden problems that can compromise their efficiency and reliability. Electrical troubleshooting emerges as a crucial technique in identifying these concealed issues. By delving into real-world case studies, we can better understand how electrical troubleshooting effectively uncovers hidden HVAC problems.


One illustrative case involves a commercial office building experiencing inconsistent temperatures across different floors. Despite routine HVAC maintenance checks, the issue persisted, leading to employee discomfort and complaints. It was not until an experienced technician employed electrical troubleshooting techniques that the root cause was identified: a faulty thermostat wire causing intermittent communication between the control system and HVAC units. By tracing electrical pathways with precision tools like multimeters and oscilloscopes, the technician pinpointed the defective wiring that standard visual inspections had overlooked.


Another compelling example occurred in a hospital setting where unexplained spikes in energy consumption were raising operational costs significantly. The facilities team initially suspected aging equipment or increased usage patterns but found no concrete evidence through standard checks.

How Electrical Troubleshooting Identifies Hidden HVAC Issues - duct cleaning

  1. HVAC installation
  2. variable refrigerant flow (VRF) systems
  3. airflow balancing
Electrical troubleshooting revealed the true culprit: several malfunctioning sensors within the HVAC control system were inaccurately reporting data, prompting unnecessary cooling cycles. This discovery was made by systematically testing sensor outputs against baseline readings using advanced diagnostic equipment, highlighting how electrical troubleshooting can detect faults invisible to conventional methods.


In yet another scenario set within a large retail space, patrons frequently reported stuffiness despite well-maintained air conditioning units. Here too, traditional inspections failed to resolve the issue until electrical diagnostics came into play. The investigation uncovered an unexpected source: electromagnetic interference from nearby heavy machinery was disrupting signals between wireless thermostats and central controllers. Utilizing spectrum analyzers and signal testers allowed technicians to identify this uncommon problem swiftly.


These case studies underscore the indispensable role of electrical troubleshooting in maintaining efficient HVAC operations. Unlike generic maintenance approaches that focus on mechanical components alone, electrical diagnostics delve deeper into the intricate web of circuits and controls governing modern HVAC systems. This method not only resolves current issues but also preemptively identifies potential failures before they escalate into costly repairs or replacements.


Moreover, leveraging electrical expertise fosters a more comprehensive understanding of system performance metrics such as voltage levels, current flows, and signal integrity-elements often neglected during superficial assessments. As buildings become smarter with integrated technologies like IoT devices and automated controls, mastering electrical troubleshooting becomes even more critical for anticipating vulnerabilities inherent in such sophisticated networks.


In conclusion, while hidden HVAC problems can elude conventional detection methods due to their complex nature or elusive symptoms, electrical troubleshooting provides a robust solution by uncovering underlying faults with precision accuracy. Through targeted analysis using specialized tools and techniques tailored for electronic systems inspection rather than mere visual checks alone-facility managers gain invaluable insights leading not only towards immediate resolution but long-term sustainability improvements too across diverse environments ranging from offices through hospitals down onto retail spaces alike!

Case Studies: Real-World Examples of Hidden HVAC Problems Uncovered through Electrical Troubleshooting
Preventative Measures and Maintenance Tips to Avoid Future Issues

Electrical troubleshooting is an essential component in maintaining the efficiency and reliability of HVAC systems. By identifying hidden electrical issues before they manifest into significant problems, we can prevent costly repairs and ensure a comfortable indoor environment. Preventative measures and maintenance tips are critical in avoiding future complications, making electrical troubleshooting not just a reactive process but a proactive strategy.


One of the fundamental preventative measures is conducting regular inspections of the HVAC system's electrical components. This includes checking for loose connections, frayed wires, or signs of corrosion that could lead to short circuits or complete system failures. Regular inspection allows for early detection of potential hazards, ensuring that these issues can be addressed promptly before they escalate.


Routine maintenance also involves testing the system’s voltage and current levels to ensure they are within the recommended parameters. Fluctuations in power supply can indicate underlying problems such as overloaded circuits or faulty components that might not be immediately visible but could lead to severe damage over time. By monitoring these electrical parameters regularly, technicians can adjust them as needed to maintain optimal performance and prevent future breakdowns.


Moreover, keeping an eye on circuit breakers and fuses is another crucial tip in preventing HVAC issues. These components protect the system from power surges by interrupting the flow of electricity when necessary. If they frequently trip or blow, it may indicate deeper issues within the electrical wiring or equipment overloads that need immediate attention.


Another critical aspect of preventative maintenance is ensuring proper grounding of the HVAC units. Grounding provides a pathway for excess electricity to safely dissipate into the earth, reducing the risk of electric shock and equipment damage during power surges or lightning strikes. Regularly checking grounding connections ensures this protective measure remains effective.


Incorporating surge protection devices can further safeguard HVAC systems from unexpected power spikes that could cause irreversible damage to sensitive electronic components. These devices absorb excess voltage before it reaches critical parts of the system, extending their lifespan and minimizing downtime caused by sudden electrical failures.


To complement regular professional check-ups, building occupants should also be educated on basic practices such as turning off units when not in use to prevent unnecessary strain on electrical systems and recognizing common warning signs like unusual noises or smells emanating from HVAC equipment.


In conclusion, by integrating thorough electrical troubleshooting with strategic preventative measures and routine maintenance tips, we can effectively identify hidden issues within HVAC systems before they develop into larger problems. This proactive approach not only enhances system reliability but also promotes safety, efficiency, and cost savings over time—ensuring that our indoor environments remain comfortable regardless of external conditions.

 

An air filter being cleaned

Indoor air quality (IAQ) is the air quality within buildings and structures. Poor indoor air quality due to indoor air pollution is known to affect the health, comfort, and well-being of building occupants. It has also been linked to sick building syndrome, respiratory issues, reduced productivity, and impaired learning in schools. Common pollutants of indoor air include: secondhand tobacco smoke, air pollutants from indoor combustion, radon, molds and other allergens, carbon monoxide, volatile organic compounds, legionella and other bacteria, asbestos fibers, carbon dioxide,[1] ozone and particulates.

Source control, filtration, and the use of ventilation to dilute contaminants are the primary methods for improving indoor air quality. Although ventilation is an integral component of maintaining good indoor air quality, it may not be satisfactory alone.[2] In scenarios where outdoor pollution would deteriorate indoor air quality, other treatment devices such as filtration may also be necessary.[3]

IAQ is evaluated through collection of air samples, monitoring human exposure to pollutants, analysis of building surfaces, and computer modeling of air flow inside buildings. IAQ is part of indoor environmental quality (IEQ), along with other factors that exert an influence on physical and psychological aspects of life indoors (e.g., lighting, visual quality, acoustics, and thermal comfort).[4]

Indoor air pollution is a major health hazard in developing countries and is commonly referred to as "household air pollution" in that context.[5] It is mostly relating to cooking and heating methods by burning biomass fuel, in the form of wood, charcoal, dung, and crop residue, in indoor environments that lack proper ventilation. Millions of people, primarily women and children, face serious health risks. In total, about three billion people in developing countries are affected by this problem. The World Health Organization (WHO) estimates that cooking-related indoor air pollution causes 3.8 million annual deaths.[6] The Global Burden of Disease study estimated the number of deaths in 2017 at 1.6 million.[7]

Definition

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For health reasons it is crucial to breathe clean air, free from chemicals and toxicants as much as possible. It is estimated that humans spend approximately 90% of their lifetime indoors[8] and that indoor air pollution in some places can be much worse than that of the ambient air.[9][10]

Various factors contribute to high concentrations of pollutants indoors, ranging from influx of pollutants from external sources, off-gassing by furniture, furnishings including carpets, indoor activities (cooking, cleaning, painting, smoking, etc. in homes to using office equipment in offices), thermal comfort parameters such as temperature, humidity, airflow and physio-chemical properties of the indoor air.[citation needed] Air pollutants can enter a building in many ways, including through open doors or windows. Poorly maintained air conditioners/ventilation systems can harbor mold, bacteria, and other contaminants, which are then circulated throughout indoor spaces, contributing to respiratory problems and allergies.

There have been many debates among indoor air quality specialists about the proper definition of indoor air quality and specifically what constitutes "acceptable" indoor air quality.

Health effects

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Share of deaths from indoor air pollution. Darker colors mean higher numbers.

IAQ is significant for human health as humans spend a large proportion of their time in indoor environments. Americans and Europeans on average spend approximately 90% of their time indoors.[11][12]

The World Health Organization (WHO) estimates that 3.2 million people die prematurely every year from illnesses attributed to indoor air pollution caused by indoor cooking, with over 237 thousand of these being children under 5. These include around an eighth of all global ischaemic heart disease, stroke, and lung cancer deaths. Overall the WHO estimated that poor indoor air quality resulted in the loss of 86 million healthy life years in 2019.[13]

Studies in the UK and Europe show exposure to indoor air pollutants, chemicals and biological contamination can irritate the upper airway system, trigger or exacerbate asthma and other respiratory or cardiovascular conditions, and may even have carcinogenic effects.[14][15][16][17][18][19]

Poor indoor air quality can cause sick building syndrome. Symptoms include burning of the eyes, scratchy throat, blocked nose, and headaches.[20]

Common pollutants

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Generated by indoor combustion

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a 3-stone stove
A traditional wood-fired 3-stone stove in Guatemala, which causes indoor air pollution

Indoor combustion, such as for cooking or heating, is a major cause of indoor air pollution and causes significant health harms and premature deaths. Hydrocarbon fires cause air pollution. Pollution is caused by both biomass and fossil fuels of various types, but some forms of fuels are more harmful than others.

Indoor fire can produce black carbon particles, nitrogen oxides, sulfur oxides, and mercury compounds, among other emissions.[21] Around 3 billion people cook over open fires or on rudimentary cook stoves. Cooking fuels are coal, wood, animal dung, and crop residues.[22] IAQ is a particular concern in low and middle-income countries where such practices are common.[23]

Cooking using natural gas (also called fossil gas, methane gas or simply gas) is associated with poorer indoor air quality. Combustion of gas produces nitrogen dioxide and carbon monixide, and can lead to increased concentrations of nitrogen dioxide throughout the home environment which is linked to respiratory issues and diseases.[24][25]

Carbon monoxide

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One of the most acutely toxic indoor air contaminants is carbon monoxide (CO), a colourless and odourless gas that is a by-product of incomplete combustion. Carbon monoxide may be emitted from tobacco smoke and generated from malfunctioning fuel burning stoves (wood, kerosene, natural gas, propane) and fuel burning heating systems (wood, oil, natural gas) and from blocked flues connected to these appliances.[26] In developed countries the main sources of indoor CO emission come from cooking and heating devices that burn fossil fuels and are faulty, incorrectly installed or poorly maintained.[27] Appliance malfunction may be due to faulty installation or lack of maintenance and proper use.[26] In low- and middle-income countries the most common sources of CO in homes are burning biomass fuels and cigarette smoke.[27]

Health effects of CO poisoning may be acute or chronic and can occur unintentionally or intentionally (self-harm). By depriving the brain of oxygen, acute exposure to carbon monoxide may have effects on the neurological system (headache, nausea, dizziness, alteration in consciousness and subjective weakness), the cardiovascular and respiratory systems (myocardial infarction, shortness of breath, or rapid breathing, respiratory failure). Acute exposure can also lead to long-term neurological effects such as cognitive and behavioural changes. Severe CO poisoning may lead to unconsciousness, coma and death. Chronic exposure to low concentrations of carbon monoxide may lead to lethargy, headaches, nausea, flu-like symptoms and neuropsychological and cardiovascular issues.[28][26]

The WHO recommended levels of indoor CO exposure in 24 hours is 4 mg/m3.[29] Acute exposure should not exceed 10 mg/m3 in 8 hours, 35 mg/m3 in one hour and 100 mg/m3 in 15 minutes.[27]

Secondhand tobacco smoke

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Secondhand smoke is tobacco smoke which affects people other than the 'active' smoker. It is made up of the exhaled smoke (15%) and mostly of smoke coming from the burning end of the cigarette, known as sidestream smoke (85%).[30]

Secondhand smoke contains more than 7000 chemicals, of which hundreds are harmful to health.[30] Secondhand tobacco smoke includes both a gaseous and a particulate materials which, with particular hazards arising from levels of carbon monoxide and very small particulates (fine particulate matter, especially PM2.5 and PM10) which get into the bronchioles and alveoles in the lung.[31] Inhaling secondhand smoke on multiple occasions can cause asthma, pneumonia, lung cancer, and sudden infant death syndrome, among other conditions.[32]

Thirdhand smoke (THS) refers to chemicals that settle on objects and bodies indoors after smoking. Exposure to thirdhand smoke can happen even after the actual cigarette smoke is not present anymore and affect those entering the indoor environment much later. Toxic substances of THS can react with other chemicals in the air and produce new toxic chemicals that are otherwise not present in cigarettes.[33]

The only certain method to improve indoor air quality as regards secondhand smoke is to eliminate smoking indoors.[34] Indoor e-cigarette use also increases home particulate matter concentrations.[35]

Particulates

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Atmospheric particulate matter, also known as particulates, can be found indoors and can affect the health of occupants. Indoor particulate matter can come from different indoor sources or be created as secondary aerosols through indoor gas-to-particle reactions. They can also be outdoor particles that enter indoors. These indoor particles vary widely in size, ranging from nanomet (nanoparticles/ultrafine particles emitted from combustion sources) to micromet (resuspensed dust).[36] Particulate matter can also be produced through cooking activities. Frying produces higher concentrations than boiling or grilling and cooking meat produces higher concentrations than cooking vegetables.[37] Preparing a Thanksgiving dinner can produce very high concentrations of particulate matter, exceeding 300 μg/m3.[38]

Particulates can penetrate deep into the lungs and brain from blood streams, causing health problems such as heart disease, lung disease, cancer and preterm birth.[39]

Generated from building materials, furnishing and consumer products

[edit]

Volatile organic compounds

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Volatile organic compounds (VOCs) include a variety of chemicals, some of which may have short- and long-term adverse health effects. There are numerous sources of VOCs indoors, which means that their concentrations are consistently higher indoors (up to ten times higher) than outdoors.[40] Some VOCs are emitted directly indoors, and some are formed through the subsequent chemical reactions that can occur in the gas-phase, or on surfaces.[41][42] VOCs presenting health hazards include benzene, formaldehyde, tetrachloroethylene and trichloroethylene.[43]

VOCs are emitted by thousands of indoor products. Examples include: paints, varnishes, waxes and lacquers, paint strippers, cleaning and personal care products, pesticides, building materials and furnishings, office equipment such as copiers and printers, correction fluids and carbonless copy paper, graphics and craft materials including glues and adhesives, permanent markers, and photographic solutions.[44] Chlorinated drinking water releases chloroform when hot water is used in the home. Benzene is emitted from fuel stored in attached garages.

Human activities such as cooking and cleaning can also emit VOCs.[45][46] Cooking can release long-chain aldehydes and alkanes when oil is heated and terpenes can be released when spices are prepared and/or cooked.[45] Leaks of natural gas from cooking appliances have been linked to elevated levels of VOCs including benzene in homes in the USA.[47] Cleaning products contain a range of VOCs, including monoterpenes, sesquiterpenes, alcohols and esters. Once released into the air, VOCs can undergo reactions with ozone and hydroxyl radicals to produce other VOCs, such as formaldehyde.[46]

Health effects include eye, nose, and throat irritation; headaches, loss of coordination, nausea; and damage to the liver, kidney, and central nervous system.[48]

Testing emissions from building materials used indoors has become increasingly common for floor coverings, paints, and many other important indoor building materials and finishes.[49] Indoor materials such as gypsum boards or carpet act as VOC 'sinks', by trapping VOC vapors for extended periods of time, and releasing them by outgassing. The VOCs can also undergo transformation at the surface through interaction with ozone.[42] In both cases, these delayed emissions can result in chronic and low-level exposures to VOCs.[50]

Several initiatives aim to reduce indoor air contamination by limiting VOC emissions from products. There are regulations in France and in Germany, and numerous voluntary ecolabels and rating systems containing low VOC emissions criteria such as EMICODE,[51] M1,[52] Blue Angel[53] and Indoor Air Comfort[54] in Europe, as well as California Standard CDPH Section 01350[55] and several others in the US. Due to these initiatives an increasing number of low-emitting products became available to purchase.

At least 18 microbial VOCs (MVOCs) have been characterised[56][57] including 1-octen-3-ol (mushroom alcohol), 3-Methylfuran, 2-pentanol, 2-hexanone, 2-heptanone, 3-octanone, 3-octanol, 2-octen-1-ol, 1-octene, 2-pentanone, 2-nonanone, borneol, geosmin, 1-butanol, 3-methyl-1-butanol, 3-methyl-2-butanol, and thujopsene. The last four are products of Stachybotrys chartarum, which has been linked with sick building syndrome.[56]

Asbestos fibers

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Many common building materials used before 1975 contain asbestos, such as some floor tiles, ceiling tiles, shingles, fireproofing, heating systems, pipe wrap, taping muds, mastics, and other insulation materials. Normally, significant releases of asbestos fiber do not occur unless the building materials are disturbed, such as by cutting, sanding, drilling, or building remodelling. Removal of asbestos-containing materials is not always optimal because the fibers can be spread into the air during the removal process. A management program for intact asbestos-containing materials is often recommended instead.

When asbestos-containing material is damaged or disintegrates, microscopic fibers are dispersed into the air. Inhalation of asbestos fibers over long exposure times is associated with increased incidence of lung cancer, mesothelioma, and asbestosis. The risk of lung cancer from inhaling asbestos fibers is significantly greater for smokers. The symptoms of disease do not usually appear until about 20 to 30 years after the first exposure to asbestos.

Although all asbestos is hazardous, products that are friable, e.g. sprayed coatings and insulation, pose a significantly higher hazard as they are more likely to release fibers to the air.[58]

Microplastics

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Microplastic is a type of airborne particulates and is found to prevail in air.[59][60][61][62] A 2017 study found indoor airborne microfiber concentrations between 1.0 and 60.0 microfibers per cubic meter (33% of which were found to be microplastics).[63] Airborne microplastic dust can be produced during renovation, building, bridge and road reconstruction projects[64] and the use of power tools.[65]

Ozone

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Indoors ozone (O3) is produced by certain high-voltage electric devices (such as air ionizers), and as a by-product of other types of pollution. It appears in lower concentrations indoors than outdoors, usually at 0.2-0.7 of the outdoor concentration.[66] Typically, most ozone is lost to surface reactions indoors, rather than to reactions in air, due to the large surface to volume ratios found indoors.[67]

Outdoor air used for ventilation may have sufficient ozone to react with common indoor pollutants as well as skin oils and other common indoor air chemicals or surfaces. Particular concern is warranted when using "green" cleaning products based on citrus or terpene extracts, because these chemicals react very quickly with ozone to form toxic and irritating chemicals[46] as well as fine and ultrafine particles.[68] Ventilation with outdoor air containing elevated ozone concentrations may complicate remediation attempts.[69]

The WHO standard for ozone concentration is 60 μg/m3 for long-term exposure and 100 μg/m3 as the maximum average over an 8-hour period.[29] The EPA standard for ozone concentration is 0.07 ppm average over an 8-hour period.[70]

Biological agents

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Mold and other allergens

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Occupants in buildings can be exposed to fungal spores, cell fragments, or mycotoxins which can arise from a host of means, but there are two common classes: (a) excess moisture induced growth of mold colonies and (b) natural substances released into the air such as animal dander and plant pollen.[71]

While mold growth is associated with high moisture levels,[72] it is likely to grow when a combination of favorable conditions arises. As well as high moisture levels, these conditions include suitable temperatures, pH and nutrient sources.[73] Mold grows primarily on surfaces, and it reproduces by releasing spores, which can travel and settle in different locations. When these spores experience appropriate conditions, they can germinate and lead to mycelium growth.[74] Different mold species favor different environmental conditions to germinate and grow, some being more hydrophilic (growing at higher levels of relative humidity) and other more xerophilic (growing at levels of relative humidity as low as 75–80%).[74][75]

Mold growth can be inhibited by keeping surfaces at conditions that are further from condensation, with relative humidity levels below 75%. This usually translates to a relative humidity of indoor air below 60%, in agreement with the guidelines for thermal comfort that recommend a relative humidity between 40 and 60 %. Moisture buildup in buildings may arise from water penetrating areas of the building envelope or fabric, from plumbing leaks, rainwater or groundwater penetration, or from condensation due to improper ventilation, insufficient heating or poor thermal quality of the building envelope.[76] Even something as simple as drying clothes indoors on radiators can increase the risk of mold growth, if the humidity produced is not able to escape the building via ventilation.[77]

Mold predominantly affects the airways and lungs. Known effects of mold on health include asthma development and exacerbation,[78] with children and elderly at greater risk of more severe health impacts.[79] Infants in homes with mold have a much greater risk of developing asthma and allergic rhinitis.[80][71] More than half of adult workers in moldy or humid buildings suffer from nasal or sinus symptoms due to mold exposure.[71] Some varieties of mold contain toxic compounds (mycotoxins). However, exposure to hazardous levels of mycotoxin via inhalation is not possible in most cases, as toxins are produced by the fungal body and are not at significant levels in the released spores.

Legionella

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Legionnaires' disease is caused by a waterborne bacterium Legionella that grows best in slow-moving or still, warm water. The primary route of exposure is through the creation of an aerosol effect, most commonly from evaporative cooling towers or showerheads. A common source of Legionella in commercial buildings is from poorly placed or maintained evaporative cooling towers, which often release water in an aerosol which may enter nearby ventilation intakes. Outbreaks in medical facilities and nursing homes, where patients are immuno-suppressed and immuno-weak, are the most commonly reported cases of Legionellosis. More than one case has involved outdoor fountains at public attractions. The presence of Legionella in commercial building water supplies is highly under-reported, as healthy people require heavy exposure to acquire infection.

Legionella testing typically involves collecting water samples and surface swabs from evaporative cooling basins, shower heads, faucets/taps, and other locations where warm water collects. The samples are then cultured and colony forming units (cfu) of Legionella are quantified as cfu/liter.

Legionella is a parasite of protozoans such as amoeba, and thus requires conditions suitable for both organisms. The bacterium forms a biofilm which is resistant to chemical and antimicrobial treatments, including chlorine. Remediation for Legionella outbreaks in commercial buildings vary, but often include very hot water flushes (160 °F (71 °C)), sterilisation of standing water in evaporative cooling basins, replacement of shower heads, and, in some cases, flushes of heavy metal salts. Preventive measures include adjusting normal hot water levels to allow for 120 °F (49 °C) at the tap, evaluating facility design layout, removing faucet aerators, and periodic testing in suspect areas.

Other bacteria

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Airborne bacteria

There are many bacteria of health significance found in indoor air and on indoor surfaces. The role of microbes in the indoor environment is increasingly studied using modern gene-based analysis of environmental samples. Currently, efforts are under way to link microbial ecologists and indoor air scientists to forge new methods for analysis and to better interpret the results.[81]

A large fraction of the bacteria found in indoor air and dust are shed from humans. Among the most important bacteria known to occur in indoor air are Mycobacterium tuberculosis, Staphylococcus aureus, Streptococcus pneumoniae.[citation needed]

Virus

[edit]
Ninth floor layout of the Metropole Hotel in Hong Kong, showing where an outbreak of the severe acute respiratory syndrome (SARS) occurred

Viruses can also be a concern for indoor air quality. During the 2002–2004 SARS outbreak, virus-laden aerosols were found to have seeped into bathrooms from the bathroom floor drains, exacerbated by the draw of bathroom exhaust fans, resulting in the rapid spread of SARS in Amoy Gardens in Hong Kong.[82][83] Elsewhere in Hong Kong, SARS CoV RNA was found on the carpet and in the air intake vents of the Metropole Hotel, which showed that secondary environmental contamination could generate infectious aerosols and resulted in superspreading events.[84]

Carbon dioxide

[edit]

Humans are the main indoor source of carbon dioxide (CO2) in most buildings. Indoor CO2 levels are an indicator of the adequacy of outdoor air ventilation relative to indoor occupant density and metabolic activity.

Indoor CO2 levels above 500 ppm can lead to higher blood pressure and heart rate, and increased peripheral blood circulation.[85] With CO2 concentrations above 1000 ppm cognitive performance might be affected, especially when doing complex tasks, making decision making and problem solving slower but not less accurate.[86][87] However, evidence on the health effects of CO2 at lower concentrations is conflicting and it is difficult to link CO2 to health impacts at exposures below 5000 ppm – reported health outcomes may be due to the presence of human bioeffluents, and other indoor air pollutants related to inadequate ventilation.[88]

Indoor carbon dioxide concentrations can be used to evaluate the quality of a room or a building's ventilation.[89] To eliminate most complaints caused by CO2, the total indoor CO2 level should be reduced to a difference of no greater than 700 ppm above outdoor levels.[90] The National Institute for Occupational Safety and Health (NIOSH) considers that indoor air concentrations of carbon dioxide that exceed 1000 ppm are a marker suggesting inadequate ventilation.[91] The UK standards for schools say that carbon dioxide levels of 800 ppm or lower indicate that the room is well-ventilated.[92] Regulations and standards from around the world show that CO2 levels below 1000 ppm represent good IAQ, between 1000 and 1500 ppm represent moderate IAQ and greater than 1500 ppm represent poor IAQ.[88]

Carbon dioxide concentrations in closed or confined rooms can increase to 1,000 ppm within 45 minutes of enclosure. For example, in a 3.5-by-4-metre (11 ft × 13 ft) sized office, atmospheric carbon dioxide increased from 500 ppm to over 1,000 ppm within 45 minutes of ventilation cessation and closure of windows and doors.[93]

Radon

[edit]

Radon is an invisible, radioactive atomic gas that results from the radioactive decay of radium, which may be found in rock formations beneath buildings or in certain building materials themselves.

Radon is probably the most pervasive serious hazard for indoor air in the United States and Europe. It is a major cause of lung cancer, responsible for 3–14% of cases in countries, leading to tens of thousands of deaths.[94]

Radon gas enters buildings as a soil gas. As it is a heavy gas it will tend to accumulate at the lowest level. Radon may also be introduced into a building through drinking water particularly from bathroom showers. Building materials can be a rare source of radon, but little testing is carried out for stone, rock or tile products brought into building sites; radon accumulation is greatest for well insulated homes.[95] There are simple do-it-yourself kits for radon gas testing, but a licensed professional can also check homes.

The half-life for radon is 3.8 days, indicating that once the source is removed, the hazard will be greatly reduced within a few weeks. Radon mitigation methods include sealing concrete slab floors, basement foundations, water drainage systems, or by increasing ventilation.[96] They are usually cost effective and can greatly reduce or even eliminate the contamination and the associated health risks.[citation needed]

Radon is measured in picocuries per liter of air (pCi/L) or becquerel per cubic meter (Bq m-3). Both are measurements of radioactivity. The World Health Organization (WHO) sets the ideal indoor radon levels at 100 Bq/m-3.[97] In the United States, it is recommend to fix homes with radon levels at or above 4 pCi/L. At the same time it is also recommends that people think about fixing their homes for radon levels between 2 pCi/L and 4 pCi/L.[98] In the United Kingdom the ideal is presence of radon indoors is 100 Bq/m-3. Action needs to be taken in homes with 200 Bq/m−3 or more.[99]

Interactive maps of radon affected areas are available for various regions and countries of the world.[100][101][102]

IAQ and climate change

[edit]

Indoor air quality is linked inextricably to outdoor air quality. The Intergovernmental Panel on Climate Change (IPCC) has varying scenarios that predict how the climate will change in the future.[103] Climate change can affect indoor air quality by increasing the level of outdoor air pollutants such as ozone and particulate matter, for example through emissions from wildfires caused by extreme heat and drought.[104][105] Numerous predictions for how indoor air pollutants will change have been made,[106][107][108][109] and models have attempted to predict how the forecasted IPCC scenarios will vary indoor air quality and indoor comfort parameters such as humidity and temperature.[110]

The net-zero challenge requires significant changes in the performance of both new and retrofitted buildings. However, increased energy efficient housing will trap pollutants inside, whether produced indoors or outdoors, and lead to an increase in human exposure.[111][112]

Indoor air quality standards and monitoring

[edit]

Quality guidelines and standards

[edit]

For occupational exposure, there are standards, which cover a wide range of chemicals, and applied to healthy adults who are exposed over time at workplaces (usually industrial environments).These are published by organisations such as Occupational Safety and Health Administration (OSHA), the National Institute for Occupational Safety and Health (NIOSH), the UK Health and Safety Executive (HSE).

There is no consensus globally about indoor air quality standards, or health-based guidelines. However, there are regulations from some individual countries and from health organisations. For example, the World Health Organization (WHO) has published health-based global air quality guidelines for the general population that are applicable both to outdoor and indoor air,[29] as well as the WHO IAQ guidelines for selected compounds,[113] whereas the UK Health Security Agency published IAQ guidelines for selected VOCs.[114] The Scientific and Technical Committee (STC34) of the International Society of Indoor Air Quality and Climate (ISIAQ) created an open database that collects indoor environmental quality guidelines worldwide.[115] The database is focused on indoor air quality (IAQ), but is currently extended to include standards, regulations, and guidelines related to ventilation, comfort, acoustics, and lighting.[116][117]

Real-time monitoring

[edit]

Since indoor air pollutants can adversely affect human health, it is important to have real-time indoor air quality assessment/monitoring system that can help not only in the improvement of indoor air quality but also help in detection of leaks, spills in a work environment and boost energy efficiency of buildings by providing real-time feedback to the heating, ventilation, and air conditioning (HVAC) system(s).[118] Additionally, there have been enough studies that highlight the correlation between poor indoor air quality and loss of performance and productivity of workers in an office setting.[119]  

Combining the Internet of Things (IoT) technology with real-time IAQ monitoring systems has  tremendously gained momentum and popularity as interventions can be done based on the real-time sensor data and thus help in the IAQ improvement.[120]   

Improvement measures

[edit]

Indoor air quality can be addressed, achieved or maintained during the design of new buildings or as mitigating measures in existing buildings. A hierarchy of measures has been proposed by the Institute of Air Quality Management. It emphasises removing pollutant sources, reducing emissions from any remaining sources, disrupting pathways between sources and the people exposed, protecting people from exposure to pollutants, and removing people from areas with poor air quality.[121]

A report assisted by the Institute for Occupational Safety and Health of the German Social Accident Insurance can support in the systematic investigation of individual health problems arising at indoor workplaces, and in the identification of practical solutions.[122]

Source control

[edit]

HVAC design

[edit]

Environmentally sustainable design concepts include aspects of commercial and residential heating, ventilation and air-conditioning (HVAC) technologies. Among several considerations, one of the topics attended to is the issue of indoor air quality throughout the design and construction stages of a building's life.[citation needed]

One technique to reduce energy consumption while maintaining adequate air quality, is demand-controlled ventilation. Instead of setting throughput at a fixed air replacement rate, carbon dioxide sensors are used to control the rate dynamically, based on the emissions of actual building occupants.[citation needed]

One way of quantitatively ensuring the health of indoor air is by the frequency of effective turnover of interior air by replacement with outside air. In the UK, for example, classrooms are required to have 2.5 outdoor air changes per hour. In halls, gym, dining, and physiotherapy spaces, the ventilation should be sufficient to limit carbon dioxide to 1,500 ppm. In the US, ventilation in classrooms is based on the amount of outdoor air per occupant plus the amount of outdoor air per unit of floor area, not air changes per hour. Since carbon dioxide indoors comes from occupants and outdoor air, the adequacy of ventilation per occupant is indicated by the concentration indoors minus the concentration outdoors. The value of 615 ppm above the outdoor concentration indicates approximately 15 cubic feet per minute of outdoor air per adult occupant doing sedentary office work where outdoor air contains over 400 ppm[123] (global average as of 2023). In classrooms, the requirements in the ASHRAE standard 62.1, Ventilation for Acceptable Indoor Air Quality, would typically result in about 3 air changes per hour, depending on the occupant density. As the occupants are not the only source of pollutants, outdoor air ventilation may need to be higher when unusual or strong sources of pollution exist indoors.

When outdoor air is polluted, bringing in more outdoor air can actually worsen the overall quality of the indoor air and exacerbate some occupant symptoms related to outdoor air pollution. Generally, outdoor country air is better than indoor city air.[citation needed]

The use of air filters can trap some of the air pollutants. Portable room air cleaners with HEPA filters can be used if ventilation is poor or outside air has high level of PM 2.5.[122] Air filters are used to reduce the amount of dust that reaches the wet coils.[citation needed] Dust can serve as food to grow molds on the wet coils and ducts and can reduce the efficiency of the coils.[citation needed]

The use of trickle vents on windows is also valuable to maintain constant ventilation. They can help prevent mold and allergen build up in the home or workplace. They can also reduce the spread of some respiratory infections.[124]

Moisture management and humidity control requires operating HVAC systems as designed. Moisture management and humidity control may conflict with efforts to conserve energy. For example, moisture management and humidity control requires systems to be set to supply make-up air at lower temperatures (design levels), instead of the higher temperatures sometimes used to conserve energy in cooling-dominated climate conditions. However, for most of the US and many parts of Europe and Japan, during the majority of hours of the year, outdoor air temperatures are cool enough that the air does not need further cooling to provide thermal comfort indoors.[citation needed] However, high humidity outdoors creates the need for careful attention to humidity levels indoors. High humidity give rise to mold growth and moisture indoors is associated with a higher prevalence of occupant respiratory problems.[citation needed]

The "dew point temperature" is an absolute measure of the moisture in air. Some facilities are being designed with dew points in the lower 50s °F, and some in the upper and lower 40s °F.[citation needed] Some facilities are being designed using desiccant wheels with gas-fired heaters to dry out the wheel enough to get the required dew points.[citation needed] On those systems, after the moisture is removed from the make-up air, a cooling coil is used to lower the temperature to the desired level.[citation needed]

Commercial buildings, and sometimes residential, are often kept under slightly positive air pressure relative to the outdoors to reduce infiltration. Limiting infiltration helps with moisture management and humidity control.

Dilution of indoor pollutants with outdoor air is effective to the extent that outdoor air is free of harmful pollutants. Ozone in outdoor air occurs indoors at reduced concentrations because ozone is highly reactive with many chemicals found indoors. The products of the reactions between ozone and many common indoor pollutants include organic compounds that may be more odorous, irritating, or toxic than those from which they are formed. These products of ozone chemistry include formaldehyde, higher molecular weight aldehydes, acidic aerosols, and fine and ultrafine particles, among others. The higher the outdoor ventilation rate, the higher the indoor ozone concentration and the more likely the reactions will occur, but even at low levels, the reactions will take place. This suggests that ozone should be removed from ventilation air, especially in areas where outdoor ozone levels are frequently high.

Effect of indoor plants

[edit]
Spider plants (Chlorophytum comosum) absorb some airborne contaminants.

Houseplants together with the medium in which they are grown can reduce components of indoor air pollution, particularly volatile organic compounds (VOC) such as benzene, toluene, and xylene. Plants remove CO2 and release oxygen and water, although the quantitative impact for house plants is small. The interest in using potted plants for removing VOCs was sparked by a 1989 NASA study conducted in sealed chambers designed to replicate the environment on space stations. However, these results suffered from poor replication[125] and are not applicable to typical buildings, where outdoor-to-indoor air exchange already removes VOCs at a rate that could only be matched by the placement of 10–1000 plants/m2 of a building's floor space.[126]

Plants also appear to reduce airborne microbes and molds, and to increase humidity.[127] However, the increased humidity can itself lead to increased levels of mold and even VOCs.[128]

Since extremely high humidity is associated with increased mold growth, allergic responses, and respiratory responses, the presence of additional moisture from houseplants may not be desirable in all indoor settings if watering is done inappropriately.[129]

Institutional programs

[edit]
EPA graphic about asthma triggers

The topic of IAQ has become popular due to the greater awareness of health problems caused by mold and triggers to asthma and allergies.

In the US, the Environmental Protection Agency (EPA) has developed an "IAQ Tools for Schools" program to help improve the indoor environmental conditions in educational institutions. The National Institute for Occupational Safety and Health conducts Health Hazard Evaluations (HHEs) in workplaces at the request of employees, authorized representative of employees, or employers, to determine whether any substance normally found in the place of employment has potentially toxic effects, including indoor air quality.[130]

A variety of scientists work in the field of indoor air quality, including chemists, physicists, mechanical engineers, biologists, bacteriologists, epidemiologists, and computer scientists. Some of these professionals are certified by organizations such as the American Industrial Hygiene Association, the American Indoor Air Quality Council and the Indoor Environmental Air Quality Council.

In the UK, under the Department for Environment Food and Rural Affairs, the Air Quality Expert Group considers current knowledge on indoor air quality and provides advice to government and devolved administration ministers.[131]

At the international level, the International Society of Indoor Air Quality and Climate (ISIAQ), formed in 1991, organizes two major conferences, the Indoor Air and the Healthy Buildings series.[132]

See also

[edit]

References

[edit]
  1. ^ Carroll, GT; Kirschman, DL; Mammana, A (2022). "Increased CO2 levels in the operating room correlate with the number of healthcare workers present: an imperative for intentional crowd control". Patient Safety in Surgery. 16 (35): 35. doi:10.1186/s13037-022-00343-8. PMC 9672642. PMID 36397098.
  2. ^ ANSI/ASHRAE Standard 62.1, Ventilation for Acceptable Indoor Air Quality, ASHRAE, Inc., Atlanta, GA, US
  3. ^ Belias, Evangelos; Licina, Dusan (2022). "Outdoor PM2. 5 air filtration: optimising indoor air quality and energy". Building & Cities. 3 (1): 186–203. doi:10.5334/bc.153.
  4. ^ KMC Controls (September 24, 2015). "What's Your IQ on IAQ and IEQ?". Archived from the original on April 12, 2021. Retrieved April 12, 2021.[unreliable source?]
  5. ^ Bruce, N; Perez-Padilla, R; Albalak, R (2000). "Indoor air pollution in developing countries: a major environmental and public health challenge". Bulletin of the World Health Organization. 78 (9): 1078–92. PMC 2560841. PMID 11019457.
  6. ^ "Household air pollution and health: fact sheet". WHO. May 8, 2018. Archived from the original on November 12, 2021. Retrieved November 21, 2020.
  7. ^ Ritchie, Hannah; Roser, Max (2019). "Access to Energy". Our World in Data. Archived from the original on November 1, 2021. Retrieved April 1, 2021. According to the Global Burden of Disease study 1.6 million people died prematurely in 2017 as a result of indoor air pollution ... But it's worth noting that the WHO publishes a substantially larger number of indoor air pollution deaths..
  8. ^ Klepeis, Neil E; Nelson, William C; Ott, Wayne R; Robinson, John P; Tsang, Andy M; Switzer, Paul; Behar, Joseph V; Hern, Stephen C; Engelmann, William H (July 2001). "The National Human Activity Pattern Survey (NHAPS): a resource for assessing exposure to environmental pollutants". Journal of Exposure Science & Environmental Epidemiology. 11 (3): 231–252. Bibcode:2001JESEE..11..231K. doi:10.1038/sj.jea.7500165. PMID 11477521. S2CID 22445147. Archived from the original on March 28, 2023. Retrieved March 30, 2024.
  9. ^ U.S. Environmental Protection Agency. Office equipment: design, indoor air emissions, and pollution prevention opportunities. Air and Energy Engineering Research Laboratory, Research Triangle Park, 1995.
  10. ^ U.S. Environmental Protection Agency. Unfinished business: a comparative assessment of environmental problems, EPA-230/2-87-025a-e (NTIS PB88-127030). Office of Policy, Planning and Evaluation, Washington, DC, 1987.
  11. ^ Klepeis, Neil E; Nelson, William C; Ott, Wayne R; Robinson, John P; Tsang, Andy M; Switzer, Paul; Behar, Joseph V; Hern, Stephen C; Engelmann, William H (July 1, 2001). "The National Human Activity Pattern Survey (NHAPS): a resource for assessing exposure to environmental pollutants". Journal of Exposure Science & Environmental Epidemiology. 11 (3): 231–252. Bibcode:2001JESEE..11..231K. doi:10.1038/sj.jea.7500165. ISSN 1559-0631. PMID 11477521. Archived from the original on November 13, 2023. Retrieved November 13, 2023.
  12. ^ "Combined or multiple exposure to health stressors in indoor built environments: an evidence-based review prepared for the WHO training workshop "Multiple environmental exposures and risks": 16–18 October 2013, Bonn, Germany". World Health Organization. Regional Office for Europe. 2014. Archived from the original on November 6, 2023. Retrieved April 10, 2024.
  13. ^ "Household air pollution". World Health Organization. December 15, 2023. Archived from the original on November 12, 2021. Retrieved April 10, 2024.
  14. ^ Clark, Sierra N.; Lam, Holly C. Y.; Goode, Emma-Jane; Marczylo, Emma L.; Exley, Karen S.; Dimitroulopoulou, Sani (August 2, 2023). "The Burden of Respiratory Disease from Formaldehyde, Damp and Mould in English Housing". Environments. 10 (8): 136. doi:10.3390/environments10080136. ISSN 2076-3298.
  15. ^ "Chief Medical Officer (CMO): annual reports". GOV.UK. November 16, 2023. Retrieved May 5, 2024.
  16. ^ "Project information | Indoor air quality at home | Quality standards | NICE". www.nice.org.uk. Retrieved May 5, 2024.
  17. ^ "The inside story: Health effects of indoor air quality on children and young people". RCPCH. Retrieved May 5, 2024.
  18. ^ Halios, Christos H.; Landeg-Cox, Charlotte; Lowther, Scott D.; Middleton, Alice; Marczylo, Tim; Dimitroulopoulou, Sani (September 15, 2022). "Chemicals in European residences – Part I: A review of emissions, concentrations and health effects of volatile organic compounds (VOCs)". Science of the Total Environment. 839: 156201. Bibcode:2022ScTEn.83956201H. doi:10.1016/j.scitotenv.2022.156201. ISSN 0048-9697. PMID 35623519.
  19. ^ "Literature review on chemical pollutants in indoor air in public settings for children and overview of their health effects with a focus on schools, kindergartens and day-care centres". www.who.int. Retrieved May 5, 2024.
  20. ^ Burge, P S (February 2004). "Sick building syndrome". Occupational and Environmental Medicine. 61 (2): 185–190. doi:10.1136/oem.2003.008813. PMC 1740708. PMID 14739390.
  21. ^ Apte, K; Salvi, S (2016). "Household air pollution and its effects on health". F1000Research. 5: 2593. doi:10.12688/f1000research.7552.1. PMC 5089137. PMID 27853506. Burning of natural gas not only produces a variety of gases such as sulfur oxides, mercury compounds, and particulate matter but also leads to the production of nitrogen oxides, primarily nitrogen dioxide...The burning of biomass fuel or any other fossil fuel increases the concentration of black carbon in the air
  22. ^ "Improved Clean Cookstoves". Project Drawdown. February 7, 2020. Archived from the original on December 15, 2021. Retrieved December 5, 2020.
  23. ^ WHO indoor air quality guidelines: household fuel combustion. Geneva: World Health Organization. 2014. ISBN 978-92-4-154888-5.
  24. ^ "Clearing the Air: Gas Cooking and Pollution in European Homes". CLASP. November 8, 2023. Retrieved May 5, 2024.
  25. ^ Seals, Brady; Krasner, Andee. "Gas Stoves: Health and Air Quality Impacts and Solutions". RMI. Retrieved May 5, 2024.
  26. ^ a b c Myers, Isabella (February 2022). The efficient operation of regulation and legislation: An holistic approach to understanding the effect of Carbon Monoxide on mortality (PDF). CO Research Trust.
  27. ^ a b c Penney, David; Benignus, Vernon; Kephalopoulos, Stylianos; Kotzias, Dimitrios; Kleinman, Michael; Verrier, Agnes (2010), "Carbon monoxide", WHO Guidelines for Indoor Air Quality: Selected Pollutants, World Health Organization, ISBN 978-92-890-0213-4, OCLC 696099951, archived from the original on March 8, 2021, retrieved March 18, 2024
  28. ^ "Carbon monoxide: toxicological overview". UK Health Security Agency. May 24, 2022. Retrieved April 17, 2024.
  29. ^ a b c WHO global air quality guidelines: particulate matter (PM2.5 and PM10), ozone, nitrogen dioxide, sulfur dioxide and carbon monoxide (PDF). World Health Organization. 2021. hdl:10665/345329. ISBN 978-92-4-003422-8.[page needed]
  30. ^ a b Soleimani, Farshid; Dobaradaran, Sina; De-la-Torre, Gabriel E.; Schmidt, Torsten C.; Saeedi, Reza (March 2022). "Content of toxic components of cigarette, cigarette smoke vs cigarette butts: A comprehensive systematic review". Science of the Total Environment. 813: 152667. Bibcode:2022ScTEn.81352667S. doi:10.1016/j.scitotenv.2021.152667. PMID 34963586.
  31. ^ "Considering smoking as an air pollution problem for environmental health | Environmental Performance Index". Archived from the original on September 25, 2018. Retrieved March 21, 2018.
  32. ^ Arfaeinia, Hossein; Ghaemi, Maryam; Jahantigh, Anis; Soleimani, Farshid; Hashemi, Hassan (June 12, 2023). "Secondhand and thirdhand smoke: a review on chemical contents, exposure routes, and protective strategies". Environmental Science and Pollution Research. 30 (32): 78017–78029. Bibcode:2023ESPR...3078017A. doi:10.1007/s11356-023-28128-1. PMC 10258487. PMID 37306877.
  33. ^ Arfaeinia, Hossein; Ghaemi, Maryam; Jahantigh, Anis; Soleimani, Farshid; Hashemi, Hassan (June 12, 2023). "Secondhand and thirdhand smoke: a review on chemical contents, exposure routes, and protective strategies". Environmental Science and Pollution Research. 30 (32): 78017–78029. Bibcode:2023ESPR...3078017A. doi:10.1007/s11356-023-28128-1. ISSN 1614-7499. PMC 10258487. PMID 37306877.
  34. ^ Health, CDC's Office on Smoking and (May 9, 2018). "Smoking and Tobacco Use; Fact Sheet; Secondhand Smoke". Smoking and Tobacco Use. Archived from the original on December 15, 2021. Retrieved January 14, 2019.
  35. ^ Fernández, E; Ballbè, M; Sureda, X; Fu, M; Saltó, E; Martínez-Sánchez, JM (December 2015). "Particulate Matter from Electronic Cigarettes and Conventional Cigarettes: a Systematic Review and Observational Study". Current Environmental Health Reports. 2 (4): 423–9. Bibcode:2015CEHR....2..423F. doi:10.1007/s40572-015-0072-x. PMID 26452675.
  36. ^ Vu, Tuan V.; Harrison, Roy M. (May 8, 2019). "Chemical and Physical Properties of Indoor Aerosols". In Harrison, R. M.; Hester, R. E. (eds.). Indoor Air Pollution. The Royal Society of Chemistry (published 2019). ISBN 978-1-78801-803-6.
  37. ^ Abdullahi, Karimatu L.; Delgado-Saborit, Juana Maria; Harrison, Roy M. (February 13, 2013). "Emissions and indoor concentrations of particulate matter and its specific chemical components from cooking: A review". Atmospheric Environment. 71: 260–294. Bibcode:2013AtmEn..71..260A. doi:10.1016/j.atmosenv.2013.01.061. Archived from the original on May 21, 2023. Retrieved April 11, 2024.
  38. ^ Patel, Sameer; Sankhyan, Sumit; Boedicker, Erin K.; DeCarlo, Peter F.; Farmer, Delphine K.; Goldstein, Allen H.; Katz, Erin F.; Nazaroff, William W; Tian, Yilin; Vanhanen, Joonas; Vance, Marina E. (June 16, 2020). "Indoor Particulate Matter during HOMEChem: Concentrations, Size Distributions, and Exposures". Environmental Science & Technology. 54 (12): 7107–7116. Bibcode:2020EnST...54.7107P. doi:10.1021/acs.est.0c00740. ISSN 0013-936X. PMID 32391692. Archived from the original on April 28, 2023. Retrieved April 11, 2024.
  39. ^ Thangavel, Prakash; Park, Duckshin; Lee, Young-Chul (June 19, 2022). "Recent Insights into Particulate Matter (PM2.5)-Mediated Toxicity in Humans: An Overview". International Journal of Environmental Research and Public Health. 19 (12): 7511. doi:10.3390/ijerph19127511. ISSN 1660-4601. PMC 9223652. PMID 35742761.
  40. ^ You, Bo; Zhou, Wei; Li, Junyao; Li, Zhijie; Sun, Yele (November 4, 2022). "A review of indoor Gaseous organic compounds and human chemical Exposure: Insights from Real-time measurements". Environment International. 170: 107611. Bibcode:2022EnInt.17007611Y. doi:10.1016/j.envint.2022.107611. PMID 36335895.
  41. ^ Weschler, Charles J.; Carslaw, Nicola (March 6, 2018). "Indoor Chemistry". Environmental Science & Technology. 52 (5): 2419–2428. Bibcode:2018EnST...52.2419W. doi:10.1021/acs.est.7b06387. ISSN 0013-936X. PMID 29402076. Archived from the original on November 15, 2023. Retrieved April 11, 2024.
  42. ^ a b Carter, Toby J.; Poppendieck, Dustin G.; Shaw, David; Carslaw, Nicola (January 16, 2023). "A Modelling Study of Indoor Air Chemistry: The Surface Interactions of Ozone and Hydrogen Peroxide". Atmospheric Environment. 297: 119598. Bibcode:2023AtmEn.29719598C. doi:10.1016/j.atmosenv.2023.119598.
  43. ^ Tsai, Wen-Tien (March 26, 2019). "An overview of health hazards of volatile organic compounds regulated as indoor air pollutants". Reviews on Environmental Health. 34 (1): 81–89. doi:10.1515/reveh-2018-0046. PMID 30854833.
  44. ^ "U.S. EPA IAQ – Organic chemicals". Epa.gov. August 5, 2010. Archived from the original on September 9, 2015. Retrieved March 2, 2012.
  45. ^ a b Davies, Helen L.; O'Leary, Catherine; Dillon, Terry; Shaw, David R.; Shaw, Marvin; Mehra, Archit; Phillips, Gavin; Carslaw, Nicola (August 14, 2023). "A measurement and modelling investigation of the indoor air chemistry following cooking activities". Environmental Science: Processes & Impacts. 25 (9): 1532–1548. doi:10.1039/D3EM00167A. ISSN 2050-7887. PMID 37609942.
  46. ^ a b c Harding-Smith, Ellen; Shaw, David R.; Shaw, Marvin; Dillon, Terry J.; Carslaw, Nicola (January 23, 2024). "Does green mean clean? Volatile organic emissions from regular versus green cleaning products". Environmental Science: Processes & Impacts. 26 (2): 436–450. doi:10.1039/D3EM00439B. ISSN 2050-7887. PMID 38258874.
  47. ^ Lebel, Eric D.; Michanowicz, Drew R.; Bilsback, Kelsey R.; Hill, Lee Ann L.; Goldman, Jackson S. W.; Domen, Jeremy K.; Jaeger, Jessie M.; Ruiz, Angélica; Shonkoff, Seth B. C. (November 15, 2022). "Composition, Emissions, and Air Quality Impacts of Hazardous Air Pollutants in Unburned Natural Gas from Residential Stoves in California". Environmental Science & Technology. 56 (22): 15828–15838. Bibcode:2022EnST...5615828L. doi:10.1021/acs.est.2c02581. ISSN 0013-936X. PMC 9671046. PMID 36263944.
  48. ^ "Volatile Organic Compounds' Impact on Indoor Air Quality". United States Environmental Protection Agency. August 18, 2014. Retrieved May 23, 2024.
  49. ^ "About VOCs". January 21, 2013. Archived from the original on January 21, 2013. Retrieved September 16, 2019.
  50. ^ Oanh, Nguyen Thi Kim; Hung, Yung-Tse (2005). "Indoor Air Pollution Control". Advanced Air and Noise Pollution Control. Handbook of Environmental Engineering. Vol. 2. pp. 237–272. doi:10.1007/978-1-59259-779-6_7. ISBN 978-1-58829-359-6.
  51. ^ "Emicode". Eurofins.com. Archived from the original on September 24, 2015. Retrieved March 2, 2012.
  52. ^ "M1". Eurofins.com. Archived from the original on September 24, 2015. Retrieved March 2, 2012.
  53. ^ "Blue Angel". Eurofins.com. Archived from the original on September 24, 2015. Retrieved March 2, 2012.
  54. ^ "Indoor Air Comfort". Indoor Air Comfort. Archived from the original on February 1, 2011. Retrieved March 2, 2012.
  55. ^ "CDPH Section 01350". Eurofins.com. Archived from the original on September 24, 2015. Retrieved March 2, 2012.
  56. ^ a b "Smelly Moldy Houses". Archived from the original on December 15, 2021. Retrieved August 2, 2014.
  57. ^ Meruva, N. K.; Penn, J. M.; Farthing, D. E. (November 2004). "Rapid identification of microbial VOCs from tobacco molds using closed-loop stripping and gas chromatography/time-of-flight mass spectrometry". J Ind Microbiol Biotechnol. 31 (10): 482–8. doi:10.1007/s10295-004-0175-0. PMID 15517467. S2CID 32543591.
  58. ^ "Atmospheric carbon dioxide passes 400 ppm everywhere". Physics Today (6): 8170. 2016. Bibcode:2016PhT..2016f8170.. doi:10.1063/pt.5.029904.
  59. ^ Xie Y, Li Y, Feng Y, Cheng W, Wang Y (April 2022). "Inhalable microplastics prevails in air: Exploring the size detection limit". Environ Int. 162: 107151. Bibcode:2022EnInt.16207151X. doi:10.1016/j.envint.2022.107151. PMID 35228011.
  60. ^ Liu C, Li J, Zhang Y, Wang L, Deng J, Gao Y, Yu L, Zhang J, Sun H (July 2019). "Widespread distribution of PET and PC microplastics in dust in urban China and their estimated human exposure". Environ Int. 128: 116–124. Bibcode:2019EnInt.128..116L. doi:10.1016/j.envint.2019.04.024. PMID 31039519.
  61. ^ Yuk, Hyeonseong; Jo, Ho Hyeon; Nam, Jihee; Kim, Young Uk; Kim, Sumin (2022). "Microplastic: A particulate matter(PM) generated by deterioration of building materials". Journal of Hazardous Materials. 437. Elsevier BV: 129290. Bibcode:2022JHzM..43729290Y. doi:10.1016/j.jhazmat.2022.129290. ISSN 0304-3894. PMID 35753297.
  62. ^ Eberhard, Tiffany; Casillas, Gaston; Zarus, Gregory M.; Barr, Dana Boyd (January 6, 2024). "Systematic review of microplastics and nanoplastics in indoor and outdoor air: identifying a framework and data needs for quantifying human inhalation exposures" (PDF). Journal of Exposure Science & Environmental Epidemiology. 34 (2). Springer Science and Business Media LLC: 185–196. doi:10.1038/s41370-023-00634-x. ISSN 1559-0631. Retrieved December 19, 2024. MPs have been found in water and soil, and recent research is exposing the vast amount of them in ambient and indoor air.
  63. ^ Gasperi, Johnny; Wright, Stephanie L.; Dris, Rachid; Collard, France; Mandin, Corinne; Guerrouache, Mohamed; Langlois, Valérie; Kelly, Frank J.; Tassin, Bruno (2018). "Microplastics in air: Are we breathing it in?" (PDF). Current Opinion in Environmental Science & Health. 1: 1–5. Bibcode:2018COESH...1....1G. doi:10.1016/j.coesh.2017.10.002. S2CID 133750509. Archived (PDF) from the original on March 6, 2020. Retrieved July 11, 2019.
  64. ^ Prasittisopin, Lapyote; Ferdous, Wahid; Kamchoom, Viroon (2023). "Microplastics in construction and built environment". Developments in the Built Environment. 15. Elsevier BV. doi:10.1016/j.dibe.2023.100188. ISSN 2666-1659.
  65. ^ Galloway, Nanette LoBiondo (September 13, 2024). "Ventnor introduces ordinance to control microplastics contamination". DownBeach. Retrieved October 2, 2024.
  66. ^ Weschler, Charles J. (December 2000). "Ozone in Indoor Environments: Concentration and Chemistry: Ozone in Indoor Environments". Indoor Air. 10 (4): 269–288. doi:10.1034/j.1600-0668.2000.010004269.x. PMID 11089331. Archived from the original on April 15, 2024. Retrieved April 11, 2024.
  67. ^ Weschler, Charles J.; Nazaroff, William W (February 22, 2023). "Human skin oil: a major ozone reactant indoors". Environmental Science: Atmospheres. 3 (4): 640–661. doi:10.1039/D3EA00008G. ISSN 2634-3606. Archived from the original on April 15, 2024. Retrieved April 11, 2024.
  68. ^ Kumar, Prashant; Kalaiarasan, Gopinath; Porter, Alexandra E.; Pinna, Alessandra; KÅ‚osowski, MichaÅ‚ M.; Demokritou, Philip; Chung, Kian Fan; Pain, Christopher; Arvind, D. K.; Arcucci, Rossella; Adcock, Ian M.; Dilliway, Claire (February 20, 2021). "An overview of methods of fine and ultrafine particle collection for physicochemical characterisation and toxicity assessments". Science of the Total Environment. 756: 143553. Bibcode:2021ScTEn.75643553K. doi:10.1016/j.scitotenv.2020.143553. hdl:10044/1/84518. PMID 33239200. S2CID 227176222.
  69. ^ Apte, M. G.; Buchanan, I. S. H.; Mendell, M. J. (April 2008). "Outdoor ozone and building-related symptoms in the BASE study". Indoor Air. 18 (2): 156–170. Bibcode:2008InAir..18..156A. doi:10.1111/j.1600-0668.2008.00521.x. PMID 18333994.
  70. ^ "Eight-hour Average Ozone Concentrations | Ground-level Ozone | New England | US EPA". United States Environmental Protection Agency. Archived from the original on December 15, 2021. Retrieved September 16, 2019.
  71. ^ a b c Park, J. H.; Cox-Ganser, J. M. (2011). "Meta-Mold exposure and respiratory health in damp indoor environments". Frontiers in Bioscience. 3 (2): 757–771. doi:10.2741/e284. PMID 21196349.
  72. ^ "CDC – Mold – General Information – Facts About Mold and Dampness". December 4, 2018. Archived from the original on December 16, 2019. Retrieved June 23, 2017.
  73. ^ Singh, Dr Jagjit; Singh, Jagjit, eds. (1994). Building Mycology (1 ed.). Taylor & Francis. doi:10.4324/9780203974735. ISBN 978-1-135-82462-4.
  74. ^ a b Clarke, J.A; Johnstone, C.M; Kelly, N.J; McLean, R.C; anderson, J.A; Rowan, N.J; Smith, J.E (January 20, 1999). "A technique for the prediction of the conditions leading to mould growth in buildings". Building and Environment. 34 (4): 515–521. Bibcode:1999BuEnv..34..515C. doi:10.1016/S0360-1323(98)00023-7. Archived from the original on October 26, 2022. Retrieved April 10, 2024.
  75. ^ Vereecken, Evy; Roels, Staf (November 15, 2011). "Review of mould prediction models and their influence on mould risk evaluation". Building and Environment. 51: 296–310. doi:10.1016/j.buildenv.2011.11.003. Archived from the original on March 2, 2024. Retrieved April 11, 2024.
  76. ^ BS 5250:2021 - Management of moisture in buildings. Code of practice. British Standards Institution (BSI). October 31, 2021. ISBN 978-0-539-18975-9.
  77. ^ Madgwick, Della; Wood, Hannah (August 8, 2016). "The problem of clothes drying in new homes in the UK". Structural Survey. 34 (4/5): 320–330. doi:10.1108/SS-10-2015-0048. ISSN 0263-080X. Archived from the original on May 7, 2021. Retrieved April 11, 2024.
  78. ^ May, Neil; McGilligan, Charles; Ucci, Marcella (2017). "Health and Moisture in Buildings" (PDF). UK Centre for Moisture in Buildings. Archived (PDF) from the original on April 11, 2024. Retrieved April 11, 2024.
  79. ^ "Understanding and addressing the health risks of damp and mould in the home". GOV.UK. September 7, 2023. Archived from the original on April 10, 2024. Retrieved April 11, 2024.
  80. ^ Clark, Sierra N.; Lam, Holly C. Y.; Goode, Emma-Jane; Marczylo, Emma L.; Exley, Karen S.; Dimitroulopoulou, Sani (August 2, 2023). "The Burden of Respiratory Disease from Formaldehyde, Damp and Mould in English Housing". Environments. 10 (8): 136. doi:10.3390/environments10080136. ISSN 2076-3298.
  81. ^ Microbiology of the Indoor Environment Archived July 23, 2011, at the Wayback Machine, microbe.net
  82. ^ http://www.info.gov.hk/info/sars/pdf/amoy_e.pdf
  83. ^ https://www.info.gov.hk/info/sars/graphics/amoyannex.jpg
  84. ^ "Progress in Global Surveillance and Response Capacity 10 Years after Severe Acute Respiratory Syndrome". environmental contamination with SARS CoV RNA was identified on the carpet in front of the index case-patient's room and 3 nearby rooms (and on their door frames but not inside the rooms) and in the air intake vents near the centrally located elevators ... secondary infections occurred not in guest rooms but in the common areas of the ninth floor, such as the corridor or elevator hall. These areas could have been contaminated through body fluids (e.g., vomitus, expectorated sputum), respiratory droplets, or suspended small-particle aerosols generated by the index case-patient; other guests were then infected by fomites or aerosols while passing through these same areas. Efficient spread of SARS CoV through small-particle aerosols was observed in several superspreading events in health care settings, during an airplane flight, and in an apartment complex (12–14,16–19). This process of environmental contamination that generated infectious aerosols likely best explains the pattern of disease transmission at the Hotel Metropole.
  85. ^ Azuma, Kenichi; Kagi, Naoki; Yanagi, U.; Osawa, Haruki (December 2018). "Effects of low-level inhalation exposure to carbon dioxide in indoor environments: A short review on human health and psychomotor performance". Environment International. 121 (Pt 1): 51–56. Bibcode:2018EnInt.121...51A. doi:10.1016/j.envint.2018.08.059. PMID 30172928.
  86. ^ Du, Bowen; Tandoc, Michael (June 19, 2020). "Indoor CO2 concentrations and cognitive function: A critical review". International Journal of Indoor Environment and Health. 30 (6): 1067–1082. Bibcode:2020InAir..30.1067D. doi:10.1111/ina.12706. PMID 32557862. S2CID 219915861.
  87. ^ Fan, Yuejie; Cao, Xiaodong; Zhang, Jie; Lai, Dayi; Pang, Liping (June 1, 2023). "Short-term exposure to indoor carbon dioxide and cognitive task performance: A systematic review and meta-analysis". Building and Environment. 237: 110331. Bibcode:2023BuEnv.23710331F. doi:10.1016/j.buildenv.2023.110331.
  88. ^ a b Lowther, Scott D.; Dimitroulopoulou, Sani; Foxall, Kerry; Shrubsole, Clive; Cheek, Emily; Gadeberg, Britta; Sepai, Ovnair (November 16, 2021). "Low Level Carbon Dioxide Indoors—A Pollution Indicator or a Pollutant? A Health-Based Perspective". Environments. 8 (11): 125. doi:10.3390/environments8110125. ISSN 2076-3298.
  89. ^ Persily, Andrew (July 2022). "Development and application of an indoor carbon dioxide metric". Indoor Air. 32 (7): e13059. doi:10.1111/ina.13059. PMID 35904382.
  90. ^ "Indoor Environmental Quality: HVAC Management | NIOSH | CDC". www.cdc.gov. February 25, 2022. Archived from the original on April 1, 2022. Retrieved April 1, 2022.
  91. ^ Indoor Environmental Quality: Building Ventilation Archived January 20, 2022, at the Wayback Machine. National Institute for Occupational Safety and Health. Accessed October 8, 2008.
  92. ^ "SAMHE - Schools' Air quality Monitoring for Health and Education". samhe.org.uk. Archived from the original on March 18, 2024. Retrieved March 18, 2024.
  93. ^ "Document Display | NEPIS | US EPA". nepis.epa.gov. Archived from the original on November 16, 2023. Retrieved October 19, 2023.
  94. ^ Zeeb & Shannoun 2009, p. 3.
  95. ^ C.Michael Hogan and Sjaak Slanina. 2010, Air pollution. Encyclopedia of Earth Archived October 12, 2006, at the Wayback Machine. eds. Sidney Draggan and Cutler Cleveland. National Council for Science and the Environment. Washington DC
  96. ^ "Radon Mitigation Methods". Radon Solution—Raising Radon Awareness. Archived from the original on December 15, 2008. Retrieved December 2, 2008.
  97. ^ Zeeb & Shannoun 2009, p. [page needed].
  98. ^ "Basic radon facts" (PDF). US Environmental Protection Agency. Archived (PDF) from the original on January 13, 2022. Retrieved September 18, 2018. Public Domain This article incorporates text from this source, which is in the public domain.
  99. ^ "Radon Action Level and Target Level". UKradon. Archived from the original on March 18, 2024. Retrieved March 18, 2024.
  100. ^ "Radon Zone Map (with State Information)". U.S. Environmental Protection Agency. Archived from the original on April 1, 2023. Retrieved April 10, 2024.
  101. ^ "UK maps of radon". UKradon. Archived from the original on March 7, 2024. Retrieved April 10, 2024.
  102. ^ "Radon map of Australia". Australian Radiation Protection and Nuclear Safety Agency (ARPANSA). Archived from the original on March 20, 2024. Retrieved April 10, 2024.
  103. ^ "Climate Change 2021: The Physical Science Basis". Intergovernmental Panel on Climate Change. Archived (PDF) from the original on May 26, 2023. Retrieved April 15, 2024.
  104. ^ Chen, Guochao; Qiu, Minghao; Wang, Peng; Zhang, Yuqiang; Shindell, Drew; Zhang, Hongliang (July 19, 2024). "Continuous wildfires threaten public and ecosystem health under climate change across continents". Frontiers of Environmental Science & Engineering. 18 (10). doi:10.1007/s11783-024-1890-6. ISSN 2095-2201.
  105. ^ Gherasim, Alina; Lee, Alison G.; Bernstein, Jonathan A. (November 14, 2023). "Impact of Climate Change on Indoor Air Quality". Immunology and Allergy Clinics of North America. 44 (1): 55–73. doi:10.1016/j.iac.2023.09.001. PMID 37973260. Archived from the original on November 15, 2023. Retrieved April 15, 2024.
  106. ^ Lacressonnière, Gwendoline; Watson, Laura; Gauss, Michael; Engardt, Magnuz; Andersson, Camilla; Beekmann, Matthias; Colette, Augustin; Foret, Gilles; Josse, Béatrice; Marécal, Virginie; Nyiri, Agnes; Siour, Guillaume; Sobolowski, Stefan; Vautard, Robert (February 1, 2017). "Particulate matter air pollution in Europe in a +2 °C warming world". Atmospheric Environment. 154: 129–140. Bibcode:2017AtmEn.154..129L. doi:10.1016/j.atmosenv.2017.01.037. Archived from the original on November 17, 2023. Retrieved April 15, 2024.
  107. ^ Lee, J; Lewis, A; Monks, P; Jacob, M; Hamilton, J; Hopkins, J; Watson, N; Saxton, J; Ennis, C; Carpenter, L (September 26, 2006). "Ozone photochemistry and elevated isoprene during the UK heatwave of august 2003". Atmospheric Environment. 40 (39): 7598–7613. Bibcode:2006AtmEn..40.7598L. doi:10.1016/j.atmosenv.2006.06.057. Archived from the original on October 26, 2022. Retrieved April 15, 2024.
  108. ^ Salthammer, Tunga; Schieweck, Alexandra; Gu, Jianwei; Ameri, Shaghayegh; Uhde, Erik (August 7, 2018). "Future trends in ambient air pollution and climate in Germany – Implications for the indoor environment". Building and Environment. 143: 661–670. Bibcode:2018BuEnv.143..661S. doi:10.1016/j.buildenv.2018.07.050.
  109. ^ Zhong, L.; Lee, C.-S.; Haghighat, F. (December 1, 2016). "Indoor ozone and climate change". Sustainable Cities and Society. 28: 466–472. doi:10.1016/j.scs.2016.08.020. Archived from the original on November 28, 2022. Retrieved April 15, 2024.
  110. ^ Zhao, Jiangyue; Uhde, Erik; Salthammer, Tunga; Antretter, Florian; Shaw, David; Carslaw, Nicola; Schieweck, Alexandra (December 9, 2023). "Long-term prediction of the effects of climate change on indoor climate and air quality". Environmental Research. 243: 117804. doi:10.1016/j.envres.2023.117804. PMID 38042519.
  111. ^ Niculita-Hirzel, Hélène (March 16, 2022). "Latest Trends in Pollutant Accumulations at Threatening Levels in Energy-Efficient Residential Buildings with and without Mechanical Ventilation: A Review". International Journal of Environmental Research and Public Health. 19 (6): 3538. doi:10.3390/ijerph19063538. ISSN 1660-4601. PMC 8951331. PMID 35329223.
  112. ^ UK Health Security Agency (2024) [1 September 2012]. "Chapter 5: Impact of climate change policies on indoor environmental quality and health in UK housing". Health Effects of Climate Change (HECC) in the UK: 2023 report (published January 15, 2024).
  113. ^ World Health Organization, ed. (2010). Who guidelines for indoor air quality: selected pollutants. Copenhagen: WHO. ISBN 978-92-890-0213-4. OCLC 696099951.
  114. ^ "Air quality: UK guidelines for volatile organic compounds in indoor spaces". Public Health England. September 13, 2019. Retrieved April 17, 2024.
  115. ^ "Home - IEQ Guidelines". ieqguidelines.org. Retrieved April 17, 2024.
  116. ^ Toyinbo, Oluyemi; Hägerhed, Linda; Dimitroulopoulou, Sani; Dudzinska, Marzenna; Emmerich, Steven; Hemming, David; Park, Ju-Hyeong; Haverinen-Shaughnessy, Ulla; the Scientific Technical Committee 34 of the International Society of Indoor Air Quality, Climate (April 19, 2022). "Open database for international and national indoor environmental quality guidelines". Indoor Air. 32 (4): e13028. doi:10.1111/ina.13028. ISSN 0905-6947. PMC 11099937. PMID 35481936.cite journal: CS1 maint: numeric names: authors list (link)
  117. ^ Dimitroulopoulou, Sani; DudziÅ„ska, Marzenna R.; Gunnarsen, Lars; Hägerhed, Linda; Maula, Henna; Singh, Raja; Toyinbo, Oluyemi; Haverinen-Shaughnessy, Ulla (August 4, 2023). "Indoor air quality guidelines from across the world: An appraisal considering energy saving, health, productivity, and comfort". Environment International. 178: 108127. Bibcode:2023EnInt.17808127D. doi:10.1016/j.envint.2023.108127. PMID 37544267.
  118. ^ Pitarma, Rui; Marques, Gonçalo; Ferreira, Bárbara Roque (February 2017). "Monitoring Indoor Air Quality for Enhanced Occupational Health". Journal of Medical Systems. 41 (2): 23. doi:10.1007/s10916-016-0667-2. PMID 28000117. S2CID 7372403.
  119. ^ Wyon, D. P. (August 2004). "The effects of indoor air quality on performance and productivity: The effects of IAQ on performance and productivity". Indoor Air. 14: 92–101. doi:10.1111/j.1600-0668.2004.00278.x. PMID 15330777.
  120. ^ Son, Young Joo; Pope, Zachary C.; Pantelic, Jovan (September 2023). "Perceived air quality and satisfaction during implementation of an automated indoor air quality monitoring and control system". Building and Environment. 243: 110713. Bibcode:2023BuEnv.24310713S. doi:10.1016/j.buildenv.2023.110713.
  121. ^ IAQM (2021). Indoor Air Quality Guidance: Assessment, Monitoring, Modelling and Mitigation (PDF) (Version 0.1 ed.). London: Institute of Air Quality Management.
  122. ^ a b Institute for Occupational Safety and Health of the German Social Accident Insurance. "Indoor workplaces – Recommended procedure for the investigation of working environment". Archived from the original on November 3, 2021. Retrieved June 10, 2020.
  123. ^ "Climate Change: Atmospheric Carbon Dioxide | NOAA Climate.gov". www.climate.gov. April 9, 2024. Retrieved May 6, 2024.
  124. ^ "Ventilation to reduce the spread of respiratory infections, including COVID-19". GOV.UK. August 2, 2022. Archived from the original on January 18, 2024. Retrieved April 15, 2024.
  125. ^ Dela Cruz, Majbrit; Christensen, Jan H.; Thomsen, Jane Dyrhauge; Müller, Renate (December 2014). "Can ornamental potted plants remove volatile organic compounds from indoor air? — a review". Environmental Science and Pollution Research. 21 (24): 13909–13928. Bibcode:2014ESPR...2113909D. doi:10.1007/s11356-014-3240-x. PMID 25056742. S2CID 207272189.
  126. ^ Cummings, Bryan E.; Waring, Michael S. (March 2020). "Potted plants do not improve indoor air quality: a review and analysis of reported VOC removal efficiencies". Journal of Exposure Science & Environmental Epidemiology. 30 (2): 253–261. Bibcode:2020JESEE..30..253C. doi:10.1038/s41370-019-0175-9. PMID 31695112. S2CID 207911697.
  127. ^ Wolverton, B. C.; Wolverton, J. D. (1996). "Interior plants: their influence on airborne microbes inside energy-efficient buildings". Journal of the Mississippi Academy of Sciences. 41 (2): 100–105.
  128. ^ US EPA, OAR (July 16, 2013). "Mold". US EPA. Archived from the original on May 18, 2020. Retrieved September 16, 2019.
  129. ^ Institute of Medicine (US) Committee on Damp Indoor Spaces and Health (2004). Damp Indoor Spaces and Health. National Academies Press. ISBN 978-0-309-09193-0. PMID 25009878. Archived from the original on January 19, 2023. Retrieved March 30, 2024.[page needed]
  130. ^ "Indoor Environmental Quality". Washington, DC: US National Institute for Occupational Safety and Health. Archived from the original on December 3, 2013. Retrieved May 17, 2013.
  131. ^ Lewis, Alastair C; Allan, James; Carslaw, David; Carruthers, David; Fuller, Gary; Harrison, Roy; Heal, Mathew; Nemitz, Eiko; Reeves, Claire (2022). Indoor Air Quality (PDF) (Report). Air Quality Expert Group. doi:10.5281/zenodo.6523605. Archived (PDF) from the original on June 5, 2023. Retrieved April 15, 2024.
  132. ^ "Isiaq.Org". International Society of Indoor Air Quality and Climate. Archived from the original on January 21, 2022. Retrieved March 2, 2012.

Sources

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Monographs
Articles, radio segments, web pages

Further reading

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A digital thermostat
Honeywell's "The Round" model T87 thermostat, one of which is in the collection of the Smithsonian.
A touch screen thermostat
An electronic thermostat in a retail store

A thermostat is a regulating device component which senses the temperature of a physical system and performs actions so that the system's temperature is maintained near a desired setpoint.

Thermostats are used in any device or system that heats or cools to a setpoint temperature. Examples include building heating, central heating, air conditioners, HVAC systems, water heaters, as well as kitchen equipment including ovens and refrigerators and medical and scientific incubators. In scientific literature, these devices are often broadly classified as thermostatically controlled loads (TCLs). Thermostatically controlled loads comprise roughly 50% of the overall electricity demand in the United States.[1]

A thermostat operates as a "closed loop" control device, as it seeks to reduce the error between the desired and measured temperatures. Sometimes a thermostat combines both the sensing and control action elements of a controlled system, such as in an automotive thermostat. The word thermostat is derived from the Greek words θερμÏŒς thermos, "hot" and στατÏŒς statos, "standing, stationary".

Overview

[edit]

A thermostat exerts control by switching heating or cooling devices on or off, or by regulating the flow of a heat transfer fluid as needed, to maintain the correct temperature. A thermostat can often be the main control unit for a heating or cooling system, in applications ranging from ambient air control to automotive coolant control. Thermostats are used in any device or system that heats or cools to a setpoint temperature. Examples include building heating, central heating, and air conditioners, kitchen equipment such as ovens and refrigerators, and medical and scientific incubators.

Construction and control

[edit]

Thermostats use different types of sensors to measure temperatures and actuate control operations. Mechanical thermostats commonly use bimetallic strips, converting a temperature change into mechanical displacement, to actuate control of the heating or cooling sources. Electronic thermostats, instead, use a thermistor or other semiconductor sensor, processing temperature change as electronic signals, to control the heating or cooling equipment.

Conventional thermostats are example of "bang-bang controllers" as the controlled system either operates at full capacity once the setpoint is reached, or keeps completely off. Although it is the simplest program to implement, such control method requires to include some hysteresis in order to prevent excessively rapid cycling of the equipment around the setpoint. As a consequence, conventional thermostats cannot control temperatures very precisely. Instead, there are oscillations of a certain magnitude, usually 1-2 °C.[2] Such control is in general inaccurate, inefficient and may induce more mechanical wear; it however, allows for more cost-effective compressors compared to ones with continuously variable capacity.[3][clarification needed]

Another consideration is the time delay of the controlled system. To improve the control performance of the system, thermostats can include an "anticipator", which stops heating/cooling slightly earlier than reaching the setpoint, as the system will continue to produce heat for a short while.[4] Turning off exactly at the setpoint will cause actual temperature to exceed the desired range, known as "overshoot". Bimetallic sensors can include a physical "anticipator", which has a thin wire touched on the thermostat. When current passes the wire, a small amount of heat is generated and transferred to the bimetallic coil. Electronic thermostats have an electronic equivalent.[5]

When higher control precision is required, a PID or MPC controller is preferred. However, they are nowadays mainly adopted for industrial purposes, for example, for semiconductor manufacturing factories or museums.

Sensor types

[edit]

Early technologies included mercury thermometers with electrodes inserted directly through the glass, so that when a certain (fixed) temperature was reached the contacts would be closed by the mercury. These were accurate to within a degree of temperature.

Common sensor technologies in use today include:

These may then control the heating or cooling apparatus using:

  • Direct mechanical control
  • Electrical signals
  • Pneumatic signals

History

[edit]

Possibly the earliest recorded examples of thermostatic control were built by a Dutch innovator, Cornelis Drebbel (1572–1633), about 1620 in England. He invented a mercury thermostat to regulate the temperature of a chicken incubator.[6] This is one of the first recorded feedback-controlled devices.

Modern thermostatic control was developed in the 1830s by Andrew Ure (1778–1857), a Scottish chemist. The textile mills of the time needed a constant and steady temperature to operate optimally, so Ure designed the bimetallic thermostat, which would bend as one of the metals expanded in response to the increased temperature and cut off the energy supply.[7]

Warren S. Johnson (1847–1911), of Wisconsin, patented a bi-metal room thermostat in 1883, and two years later sought a patent for the first multi-zone thermostatic control system.[8][9] Albert Butz (1849–1905) invented the electric thermostat and patented it in 1886.

One of the first industrial uses of the thermostat was in the regulation of the temperature in poultry incubators. Charles Hearson, a British engineer, designed the first modern incubator for eggs, which was taken up for use on poultry farms in 1879.[10]

Mechanical thermostats

[edit]

This covers only devices which both sense and control using purely mechanical means.

Bimetal

[edit]

Domestic water and steam based central heating systems have traditionally been controlled by bi-metallic strip thermostats, and this is dealt with later in this article. Purely mechanical control has been localised steam or hot-water radiator bi-metallic thermostats which regulated the individual flow. However, thermostatic radiator valves (TRV) are now being widely used.

Purely mechanical thermostats are used to regulate dampers in some rooftop turbine vents, reducing building heat loss in cool or cold periods.

Some automobile passenger heating systems have a thermostatically controlled valve to regulate the water flow and temperature to an adjustable level. In older vehicles the thermostat controls the application of engine vacuum to actuators that control water valves and flappers to direct the flow of air. In modern vehicles, the vacuum actuators may be operated by small solenoids under the control of a central computer.

Wax pellet

[edit]

Automotive

[edit]
Car engine thermostat

Perhaps the most common example of purely mechanical thermostat technology in use today is the internal combustion engine cooling system thermostat, used to maintain the engine near its optimum operating temperature by regulating the flow of coolant to an air-cooled radiator. This type of thermostat operates using a sealed chamber containing a wax pellet that melts and expands at a set temperature. The expansion of the chamber operates a rod which opens a valve when the operating temperature is exceeded. The operating temperature is determined by the composition of the wax. Once the operating temperature is reached, the thermostat progressively increases or decreases its opening in response to temperature changes, dynamically balancing the coolant recirculation flow and coolant flow to the radiator to maintain the engine temperature in the optimum range.

On many automobile engines, including all Chrysler Group and General Motors products, the thermostat does not restrict flow to the heater core. The passenger side tank of the radiator is used as a bypass to the thermostat, flowing through the heater core. This prevents formation of steam pockets before the thermostat opens, and allows the heater to function before the thermostat opens. Another benefit is that there is still some flow through the radiator if the thermostat fails.

Shower and other hot water controls

[edit]

A thermostatic mixing valve uses a wax pellet to control the mixing of hot and cold water. A common application is to permit operation of an electric water heater at a temperature hot enough to kill Legionella bacteria (above 60 °C, 140 °F), while the output of the valve produces water that is cool enough to not immediately scald (49 °C, 120 °F).

Analysis

[edit]

A wax pellet driven valve can be analyzed through graphing the wax pellet's hysteresis which consists of two thermal expansion curves; extension (motion) vs. temperature increase, and contraction (motion) vs. temperature decrease. The spread between the up and down curves visually illustrate the valve's hysteresis; there is always hysteresis within wax driven valves due to the phase transition or phase change between solids and liquids. Hysteresis can be controlled with specialized blended mixes of hydrocarbons; tight hysteresis is what most desire, however some applications require broader ranges. Wax pellet driven valves are used in anti scald, freeze protection, over-temp purge, solar thermal energy or solar thermal, automotive, and aerospace applications among many others.

Gas expansion

[edit]

Thermostats are sometimes used to regulate gas ovens. It consists of a gas-filled bulb connected to the control unit by a slender copper tube. The bulb is normally located at the top of the oven. The tube ends in a chamber sealed by a diaphragm. As the thermostat heats up, the gas expands applying pressure to the diaphragm which reduces the flow of gas to the burner.

Pneumatic thermostats

[edit]

A pneumatic thermostat is a thermostat that controls a heating or cooling system via a series of air-filled control tubes. This "control air" system responds to the pressure changes (due to temperature) in the control tube to activate heating or cooling when required. The control air typically is maintained on "mains" at 15-18 psi (although usually operable up to 20 psi). Pneumatic thermostats typically provide output/ branch/ post-restrictor (for single-pipe operation) pressures of 3-15 psi which is piped to the end device (valve/ damper actuator/ pneumatic-electric switch, etc.).[11]

The pneumatic thermostat was invented by Warren Johnson in 1895[12] soon after he invented the electric thermostat. In 2009, Harry Sim was awarded a patent for a pneumatic-to-digital interface[13] that allows pneumatically controlled buildings to be integrated with building automation systems to provide similar benefits as direct digital control (DDC).

Electrical and analog electronic thermostats

[edit]

Bimetallic switching thermostats

[edit]
Bimetallic thermostat for buildings.

Water and steam based central heating systems have traditionally had overall control by wall-mounted bi-metallic strip thermostats. These sense the air temperature using the differential expansion of two metals to actuate an on/off switch.[14] Typically the central system would be switched on when the temperature drops below the setpoint on the thermostat, and switched off when it rises above, with a few degrees of hysteresis to prevent excessive switching. Bi-metallic sensing is now being superseded by electronic sensors. A principal use of the bi-metallic thermostat today is in individual electric convection heaters, where control is on/off, based on the local air temperature and the setpoint desired by the user. These are also used on air-conditioners, where local control is required.

Contact configuration nomenclature

[edit]

This follows the same nomenclature as described in Relay § Terminology and Switch § Contact terminology. A thermostat is considered to be activated by thermal energy, thus “normal” refers to the state in which temperature is below the setpoint.

  • "NO" stands for "normally open". This is the same as "COR" ("close on rise"). May be used to start a fan when it is becoming hot, and to stop the fan when it has become cold enough.
  • "NC" stands for "normally closed". This is the same as "OOR" ("open on rise"). May be used to start a heater when it is becoming cold, and to stop the heater when it has become warm enough.
  • "CO" stands for "change over". This serves both as "NO" and "NC". May be used to start a fan when it is becoming hot, but also (on the opposite terminal), to start a heater when it is becoming cold.

Any leading number stands for number of contact sets, like "1NO", "1NC" for one contact set with two terminals. "1CO" will also have one contact set, even if it is a switch-over with three terminals.

Simple two wire thermostats

[edit]
Millivolt thermostat mechanism

The illustration is the interior of a common two wire heat-only household thermostat, used to regulate a gas-fired heater via an electric gas valve. Similar mechanisms may also be used to control oil furnaces, boilers, boiler zone valves, electric attic fans, electric furnaces, electric baseboard heaters, and household appliances such as refrigerators, coffee pots and hair dryers. The power through the thermostat is provided by the heating device and may range from millivolts to 240 volts in common North American construction, and is used to control the heating system either directly (electric baseboard heaters and some electric furnaces) or indirectly (all gas, oil and forced hot water systems). Due to the variety of possible voltages and currents available at the thermostat, caution must be taken when selecting a replacement device.

  1. Setpoint control lever. This is moved to the right for a higher temperature. The round indicator pin in the center of the second slot shows through a numbered slot in the outer case.
  2. Bimetallic strip wound into a coil. The center of the coil is attached to a rotating post attached to lever (1). As the coil gets colder the moving end — carrying (4) — moves clockwise.
  3. Flexible wire. The left side is connected via one wire of a pair to the heater control valve.
  4. Moving contact attached to the bimetal coil. Thence, to the heater's controller.
  5. Fixed contact screw. This is adjusted by the manufacturer. It is connected electrically by a second wire of the pair to the thermocouple and the heater's electrically operated gas valve.
  6. Magnet. This ensures a good contact when the contact closes. It also provides hysteresis to prevent short heating cycles, as the temperature must be raised several degrees before the contacts will open. As an alternative, some thermostats instead use a mercury switch on the end of the bimetal coil. The weight of the mercury on the end of the coil tends to keep it there, also preventing short heating cycles. However, this type of thermostat is banned in many countries due to its highly and permanently toxic nature if broken. When replacing these thermostats they must be regarded as chemical waste.

Not shown in the illustration is a separate bimetal thermometer on the outer case to show the actual temperature at the thermostat.

Millivolt thermostats

[edit]

As illustrated in the use of the thermostat above, all of the power for the control system is provided by a thermopile which is a combination of many stacked thermocouples, heated by the pilot light. The thermopile produces sufficient electrical power to drive a low-power gas valve, which under control of one or more thermostat switches, in turn controls the input of fuel to the burner.

This type of device is generally considered obsolete as pilot lights can waste a surprising amount of gas (in the same way a dripping faucet can waste a large amount of water over an extended period), and are also no longer used on stoves, but are still to be found in many gas water heaters and gas fireplaces. Their poor efficiency is acceptable in water heaters, since most of the energy "wasted" on the pilot still represents a direct heat gain for the water tank. The Millivolt system also makes it unnecessary for a special electrical circuit to be run to the water heater or furnace; these systems are often completely self-sufficient and can run without any external electrical power supply. For tankless "on demand" water heaters, pilot ignition is preferable because it is faster than hot-surface ignition and more reliable than spark ignition.

Some programmable thermostats - those that offer simple "millivolt" or "two-wire" modes - will control these systems.

24-volt thermostats

[edit]

The majority of modern heating/cooling/heat pump thermostats operate on low voltage (typically 24 volts AC) control circuits. The source of the 24 volt AC power is a control transformer installed as part of the heating/cooling equipment. The advantage of the low voltage control system is the ability to operate multiple electromechanical switching devices such as relays, contactors, and sequencers using inherently safe voltage and current levels.[15] Built into the thermostat is a provision for enhanced temperature control using anticipation.

A heat anticipator generates a small amount of additional heat to the sensing element while the heating appliance is operating. This opens the heating contacts slightly early to prevent the space temperature from greatly overshooting the thermostat setting. A mechanical heat anticipator is generally adjustable and should be set to the current flowing in the heating control circuit when the system is operating.

A cooling anticipator generates a small amount of additional heat to the sensing element while the cooling appliance is not operating. This causes the contacts to energize the cooling equipment slightly early, preventing the space temperature from climbing excessively. Cooling anticipators are generally non-adjustable.

Electromechanical thermostats use resistance elements as anticipators. Most electronic thermostats use either thermistor devices or integrated logic elements for the anticipation function. In some electronic thermostats, the thermistor anticipator may be located outdoors, providing a variable anticipation depending on the outdoor temperature.

Thermostat enhancements include outdoor temperature display, programmability, and system fault indication. While such 24 volt thermostats are incapable of operating a furnace when the mains power fails, most such furnaces require mains power for heated air fans (and often also hot-surface or electronic spark ignition) rendering moot the functionality of the thermostat. In other circumstances such as piloted wall and "gravity" (fanless) floor and central heaters the low voltage system described previously may be capable of remaining functional when electrical power is unavailable.

There are no standards for wiring color codes, but convention has settled on the following terminal codes and colors.[16][17] In all cases, the manufacturer's instructions should be considered definitive.

Terminal code Color Description
R Red 24 volt (Return line to appliance; often strapped to Rh and Rc)
Rh Red 24 volt HEAT load (Return line Heat)
Rc Red 24 volt COOL load (Return line Cool)
C Black/Blue/Brown/Cyan 24 volt Common connection to relays
W / W1 White Heat
W2 Varies/White/Black 2nd Stage / Backup Heat
Y / Y1 Yellow Cool
Y2 Blue/Orange/Purple/Yellow/White 2nd Stage Cool
G Green Fan
O Varies/Orange/Black Reversing valve Energize to Cool (Heat Pump)
B Varies/Blue/Black/Brown/Orange Reversing valve Energize to Heat (Heat Pump) or Common
E Varies/Blue/Pink/Gray/Tan Emergency Heat (Heat Pump)
S1/S2 Brown/Black/Blue Temperature Sensor (Usually outdoors on a Heat Pump System)
T Varies/Tan/Gray Outdoor Anticipator Reset, Thermistor
X Varies/Black Emergency Heat (Heat Pump) or Common
X2 Varies 2nd stage/emergency heating or indicator lights
L Varies Service Light
U Varies User programmable (usually for humidifier)
K Yellow/Green Combined Y and G
PS Varies Pipe Sensor for two pipe heat/cool systems
V Varies Variable speed (many can function as W2)

Older, mostly deprecated designations:

Terminal code Description
5 / V 24 volt ac supply
4 / M 24 volt HEAT load
6 / blank Not heat to close valve
F Cool fan relay or Fault light
G Heat fan relay
H Heat valve
M Heat Pump compressor
P Heat Pump defrost
R Heat pump reversing valve
VR 24 volt auxiliary heat
Y Auxiliary heat
C Clock power (usually two terminals) or Cool relay
T Transformer common
Z Fan power source for "Auto" connection

Line-voltage thermostats

[edit]

Line voltage thermostats are most commonly used for electric space heaters such as a baseboard heater or a direct-wired electric furnace. If a line voltage thermostat is used, system power (in the United States, 120 or 240 volts) is directly switched by the thermostat. With switching current often exceeding 40 amperes, using a low voltage thermostat on a line voltage circuit will result at least in the failure of the thermostat and possibly a fire. Line voltage thermostats are sometimes used in other applications, such as the control of fan-coil (fan powered from line voltage blowing through a coil of tubing which is either heated or cooled by a larger system) units in large systems using centralized boilers and chillers, or to control circulation pumps in hydronic heating applications.

Some programmable thermostats are available to control line-voltage systems. Baseboard heaters will especially benefit from a programmable thermostat which is capable of continuous control (as are at least some Honeywell models), effectively controlling the heater like a lamp dimmer, and gradually increasing and decreasing heating to ensure an extremely constant room temperature (continuous control rather than relying on the averaging effects of hysteresis). Systems which include a fan (electric furnaces, wall heaters, etc.) must typically use simple on/off controls.

Digital electronic thermostats

[edit]
Residential digital thermostat
Lux Products' Model TX9000TS Touch Screen Thermostat.
Lux Products WIN100 Heating & Cooling Programmable Outlet Thermostat shown with control door closed and open.

Newer digital thermostats have no moving parts to measure temperature and instead rely on thermistors or other semiconductor devices such as a resistance thermometer (resistance temperature detector). Typically one or more regular batteries must be installed to operate it, although some so-called "power stealing" digital thermostats (operated for energy harvesting) use the common 24-volt AC circuits as a power source, but will not operate on thermopile powered "millivolt" circuits used in some furnaces. Each has an LCD screen showing the current temperature, and the current setting. Most also have a clock, and time-of-day and even day-of-week settings for the temperature, used for comfort and energy conservation. Some advanced models have touch screens, or the ability to work with home automation or building automation systems.

Digital thermostats use either a relay or a semiconductor device such as triac to act as a switch to control the HVAC unit. Units with relays will operate millivolt systems, but often make an audible "click" noise when switching on or off.

HVAC systems with the ability to modulate their output can be combined with thermostats that have a built-in PID controller to achieve smoother operation. There are also modern thermostats featuring adaptive algorithms to further improve the inertia prone system behaviour. For instance, setting those up so that the temperature in the morning at 7 a.m. should be 21 °C (69.8 °F), makes sure that at that time the temperature will be 21 °C (69.8 °F), where a conventional thermostat would just start working at that time. The algorithms decide at what time the system should be activated in order to reach the desired temperature at the desired time.[18] Other thermostat used for process/industrial control where on/off control is not suitable the PID control can also makes sure that the temperature is very stable (for instance, by reducing overshoots by fine tuning PID constants for set value (SV)[19] or maintaining temperature in a band by deploying hysteresis control.[20])

Most digital thermostats in common residential use in North America and Europe are programmable thermostats, which will typically provide a 30% energy savings if left with their default programs; adjustments to these defaults may increase or reduce energy savings.[21] The programmable thermostat article provides basic information on the operation, selection and installation of such a thermostat.

Thermostats and HVAC operation

[edit]

Ignition sequences in modern conventional systems

[edit]
Gas
  1. Start draft inducer fan/blower (if the furnace is relatively recent) to create a column of air flowing up the chimney
  2. Heat ignitor or start spark-ignition system
  3. Open gas valve to ignite main burners
  4. Wait (if furnace is relatively recent) until the heat exchanger is at proper operating temperature before starting main blower fan or circulator pump
Oil
Similar to gas, except rather than opening a valve, the furnace will start an oil pump to inject oil into the burner
Electric
The blower fan or circulator pump will be started, and a large electromechanical relay or TRIAC will turn on the heating elements
Coal, grain or pellet
Generally rare today (though grains such as corn, wheat, and barley, or pellets made of wood, bark, or cardboard are increasing in popularity); similar to gas, except rather than opening a valve, the furnace will start a screw to drive coal/grain/pellets into the firebox

With non-zoned (typical residential, one thermostat for the whole house) systems, when the thermostat's R (or Rh) and W terminals are connected, the furnace will go through its start-up procedure and produce heat.

With zoned systems (some residential, many commercial systems — several thermostats controlling different "zones" in the building), the thermostat will cause small electric motors to open valves or dampers and start the furnace or boiler if it is not already running.

Most programmable thermostats will control these systems.

Combination heating/cooling regulation

[edit]

Depending on what is being controlled, a forced-air air conditioning thermostat generally has an external switch for heat/off/cool, and another on/auto to turn the blower fan on constantly or only when heating and cooling are running. Four wires come to the centrally-located thermostat from the main heating/cooling unit (usually located in a closet, basement, or occasionally in the attic): One wire, usually red, supplies 24 volts AC power to the thermostat, while the other three supply control signals from the thermostat, usually white for heat, yellow for cooling, and green to turn on the blower fan. The power is supplied by a transformer, and when the thermostat makes contact between the 24 volt power and one or two of the other wires, a relay back at the heating/cooling unit activates the corresponding heat/fan/cool function of the unit(s).

A thermostat, when set to "cool", will only turn on when the ambient temperature of the surrounding room is above the set temperature. Thus, if the controlled space has a temperature normally above the desired setting when the heating/cooling system is off, it would be wise to keep the thermostat set to "cool", despite what the temperature is outside. On the other hand, if the temperature of the controlled area falls below the desired degree, then it is advisable to turn the thermostat to "heat".

Heat pump regulation

[edit]
Thermostat design

The heat pump is a refrigeration based appliance which reverses refrigerant flow between the indoor and outdoor coils. This is done by energizing a reversing valve (also known as a "4-way" or "change-over" valve). During cooling, the indoor coil is an evaporator removing heat from the indoor air and transferring it to the outdoor coil where it is rejected to the outdoor air. During heating, the outdoor coil becomes the evaporator and heat is removed from the outdoor air and transferred to the indoor air through the indoor coil. The reversing valve, controlled by the thermostat, causes the change-over from heat to cool. Residential heat pump thermostats generally have an "O" terminal to energize the reversing valve in cooling. Some residential and many commercial heat pump thermostats use a "B" terminal to energize the reversing valve in heating. The heating capacity of a heat pump decreases as outdoor temperatures fall. At some outdoor temperature (called the balance point) the ability of the refrigeration system to transfer heat into the building falls below the heating needs of the building. A typical heat pump is fitted with electric heating elements to supplement the refrigeration heat when the outdoor temperature is below this balance point. Operation of the supplemental heat is controlled by a second stage heating contact in the heat pump thermostat. During heating, the outdoor coil is operating at a temperature below the outdoor temperature and condensation on the coil may take place. This condensation may then freeze onto the coil, reducing its heat transfer capacity. Heat pumps therefore have a provision for occasional defrost of the outdoor coil. This is done by reversing the cycle to the cooling mode, shutting off the outdoor fan, and energizing the electric heating elements. The electric heat in defrost mode is needed to keep the system from blowing cold air inside the building. The elements are then used in the "reheat" function. Although the thermostat may indicate the system is in defrost and electric heat is activated, the defrost function is not controlled by the thermostat. Since the heat pump has electric heat elements for supplemental and reheats, the heat pump thermostat provides for use of the electric heat elements should the refrigeration system fail. This function is normally activated by an "E" terminal on the thermostat. When in emergency heat, the thermostat makes no attempt to operate the compressor or outdoor fan.

Thermostat location

[edit]

The thermostat should not be located on an outside wall or where it could be exposed to direct sunlight at any time during the day. It should be located away from the room's cooling or heating vents or device, yet exposed to general airflow from the room(s) to be regulated.[22] An open hallway may be most appropriate for a single zone system, where living rooms and bedrooms are operated as a single zone. If the hallway may be closed by doors from the regulated spaces then these should be left open when the system is in use. If the thermostat is too close to the source controlled then the system will tend to "short a cycle", and numerous starts and stops can be annoying and in some cases shorten equipment life. A multiple zoned system can save considerable energy by regulating individual spaces, allowing unused rooms to vary in temperature by turning off the heating and cooling.

Setback temperature

[edit]

HVAC systems take a long time, usually one to several hours, to cool down or warm up the space from near outdoor conditions in summer or winter. Thus, it is a common practice to set setback temperatures when the space is not occupied (night and/or holidays). On the one hand, compared with maintaining at the original setpoint, substantial energy consumption can be saved.[23] On the other hand, compared with turning off the system completely, it avoids room temperature drifting too much from the comfort zone, thus reducing the time of possible discomfort when the space is again occupied. New thermostats are mostly programmable and include an internal clock that allows this setback feature to be easily incorporated.

Dummy thermostats

[edit]

It has been reported that many thermostats in office buildings are non-functional dummy devices, installed to give tenants' employees an illusion of control.[24][25] These dummy thermostats are in effect a type of placebo button. However, these thermostats are often used to detect the temperature in the zone, even though their controls are disabled. This function is often referred to as "lockout".[26]

See also

[edit]

Notes and references

[edit]
  1. ^ Energy Information Administration, Residential energy consumption survey, U.S. Dept. Energy, Washington, DC, Tech. Rep., 2001.
  2. ^ thermostathub (June 26, 2023). "Easy Home Heating: Get Started with the Danfoss Wireless Thermostat". Thermostat Hub. Retrieved October 23, 2023.
  3. ^ Homod, Raad Z.; Gaeid, Khalaf S.; Dawood, Suroor M.; Hatami, Alireza; Sahari, Khairul S. (August 2020). "Evaluation of energy-saving potential for optimal time response of HVAC control system in smart buildings". Applied Energy. 271: 115255. Bibcode:2020ApEn..27115255H. doi:10.1016/j.apenergy.2020.115255. S2CID 219769422.
  4. ^ Roots, W. K. (1962). "An introduction to the assessment of line-voltage thermostat performance for electric heating applications". Transactions of the American Institute of Electrical Engineers, Part II: Applications and Industry. 81 (3): 176–183. doi:10.1109/TAI.1962.6371813. ISSN 0097-2185. S2CID 51647958.
  5. ^ James E. Brumbaugh, AudelHVAC Fundamentals: Volume 2: Heating System Components, Gas and Oil Burners, and Automatic Controls, John Wiley & Sons, 2004 ISBN 0764542079 pp. 109-119
  6. ^ "Tierie, Gerrit. Cornelis Drebbel. Amsterdam: HJ Paris, 1932" (PDF). Retrieved May 3, 2013.
  7. ^ "An Early History Of Comfort Heating". The NEWS Magazine. Troy, Michigan: BNP Media. November 6, 2001. Retrieved November 2, 2014.
  8. ^ "Thermostat Maker Deploys Climate Control Against Climate Change". America.gov. Archived from the original on April 18, 2009. Retrieved October 3, 2009.
  9. ^ "Johnson Controls Inc. | History". Johnsoncontrols.com. November 7, 2007. Retrieved October 3, 2009.
  10. ^ Falk, Cynthia G. (2012). Barns of New York: Rural Architecture of the Empire State (paperback) (First ed.). Ithaca, New York: Cornell University Press (published May 1, 2012). ISBN 978-0-8014-7780-5. Retrieved November 2, 2014.
  11. ^ "Dr-Fix-It Explains a Common Pneumatic Comfort Control Circuit". dr-fix-it.com. RTWEB. 2005. Archived from the original on December 6, 2017. Retrieved November 2, 2014.
  12. ^ Fehring, T.H., ed., Mechanical Engineering: A Century of Progress, NorCENergy Consultants, LLC, October 10, 1980 - Technology & Engineering, p. 22
  13. ^ "Pneumatic-to-digital devices, systems and methods" (PDF).
  14. ^ Salazar, Diet (October 21, 2019). "Thermostats: Everything You Need to Know". Engineer Warehouse. Retrieved March 12, 2021.
  15. ^ Electrical potentials at and below 24 volts are classed as "Safety Extra-Low Voltage" under most electrical codes when supplied through an isolation transformer.
  16. ^ Sawyer, Doc. "Thermostat Wire Color Codes". dr-fix-it.com. Archived from the original on September 23, 2015. Retrieved March 7, 2015.[1]
  17. ^ Transtronics, Inc. "Thermostat signals and wiring". wiki.xtronics.com. Retrieved March 7, 2015.
  18. ^ Honeywell smart response technology
  19. ^ "Smart PID temperature control". smartpid.com. September 19, 2016. Retrieved October 10, 2018.
  20. ^ "Temperature Controllers Using Hysteresis". panasonic.com. October 18, 2011. Retrieved October 10, 2018.
  21. ^ "Summary of Research Findings From the Programmable Thermostat Market" (PDF). Energy Star. Retrieved March 12, 2021.
  22. ^ KMC Controls. "Room Sensor and Thermostat: Mounting and Maintenance Application Guide" (PDF). Retrieved April 12, 2021.
  23. ^ Moon, Jin Woo; Han, Seung-Hoon (February 1, 2011). "Thermostat strategies impact on energy consumption in residential buildings". Energy and Buildings. 43 (2): 338–346. Bibcode:2011EneBu..43..338M. doi:10.1016/j.enbuild.2010.09.024. ISSN 0378-7788.
  24. ^ Sandberg, Jared (January 15, 2003). "Employees Only Think They Control Thermostat". The Wall Street Journal. Retrieved September 2, 2009.
  25. ^ Katrina C. Arabe (April 11, 2003). ""Dummy" Thermostats Cool Down Tempers, Not Temperatures". Retrieved February 13, 2010.
  26. ^ Example datasheet of current art thermostat, exhibiting lockout functionality : http://cgproducts.johnsoncontrols.com/MET_PDF/12011079.pdf
[edit]

 

Rooftop HVAC unit with view of fresh-air intake vent
Ventilation duct with outlet diffuser vent. These are installed throughout a building to move air in or out of rooms. In the middle is a damper to open and close the vent to allow more or less air to enter the space.
The control circuit in a household HVAC installation. The wires connecting to the blue terminal block on the upper-right of the board lead to the thermostat. The fan enclosure is directly behind the board, and the filters can be seen at the top. The safety interlock switch is at the bottom left. In the lower middle is the capacitor.

Heating, ventilation, and air conditioning (HVAC) is the use of various technologies to control the temperature, humidity, and purity of the air in an enclosed space. Its goal is to provide thermal comfort and acceptable indoor air quality. HVAC system design is a subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics, and heat transfer. "Refrigeration" is sometimes added to the field's abbreviation as HVAC&R or HVACR, or "ventilation" is dropped, as in HACR (as in the designation of HACR-rated circuit breakers).

HVAC is an important part of residential structures such as single family homes, apartment buildings, hotels, and senior living facilities; medium to large industrial and office buildings such as skyscrapers and hospitals; vehicles such as cars, trains, airplanes, ships and submarines; and in marine environments, where safe and healthy building conditions are regulated with respect to temperature and humidity, using fresh air from outdoors.

Ventilating or ventilation (the "V" in HVAC) is the process of exchanging or replacing air in any space to provide high indoor air quality which involves temperature control, oxygen replenishment, and removal of moisture, odors, smoke, heat, dust, airborne bacteria, carbon dioxide, and other gases. Ventilation removes unpleasant smells and excessive moisture, introduces outside air, keeps interior building air circulating, and prevents stagnation of the interior air. Methods for ventilating a building are divided into mechanical/forced and natural types.[1]

Overview

[edit]

The three major functions of heating, ventilation, and air conditioning are interrelated, especially with the need to provide thermal comfort and acceptable indoor air quality within reasonable installation, operation, and maintenance costs. HVAC systems can be used in both domestic and commercial environments. HVAC systems can provide ventilation, and maintain pressure relationships between spaces. The means of air delivery and removal from spaces is known as room air distribution.[2]

Individual systems

[edit]

In modern buildings, the design, installation, and control systems of these functions are integrated into one or more HVAC systems. For very small buildings, contractors normally estimate the capacity and type of system needed and then design the system, selecting the appropriate refrigerant and various components needed. For larger buildings, building service designers, mechanical engineers, or building services engineers analyze, design, and specify the HVAC systems. Specialty mechanical contractors and suppliers then fabricate, install and commission the systems. Building permits and code-compliance inspections of the installations are normally required for all sizes of buildings

District networks

[edit]

Although HVAC is executed in individual buildings or other enclosed spaces (like NORAD's underground headquarters), the equipment involved is in some cases an extension of a larger district heating (DH) or district cooling (DC) network, or a combined DHC network. In such cases, the operating and maintenance aspects are simplified and metering becomes necessary to bill for the energy that is consumed, and in some cases energy that is returned to the larger system. For example, at a given time one building may be utilizing chilled water for air conditioning and the warm water it returns may be used in another building for heating, or for the overall heating-portion of the DHC network (likely with energy added to boost the temperature).[3][4][5]

Basing HVAC on a larger network helps provide an economy of scale that is often not possible for individual buildings, for utilizing renewable energy sources such as solar heat,[6][7][8] winter's cold,[9][10] the cooling potential in some places of lakes or seawater for free cooling, and the enabling function of seasonal thermal energy storage. By utilizing natural sources that can be used for HVAC systems it can make a huge difference for the environment and help expand the knowledge of using different methods.

History

[edit]

HVAC is based on inventions and discoveries made by Nikolay Lvov, Michael Faraday, Rolla C. Carpenter, Willis Carrier, Edwin Ruud, Reuben Trane, James Joule, William Rankine, Sadi Carnot, Alice Parker and many others.[11]

Multiple inventions within this time frame preceded the beginnings of the first comfort air conditioning system, which was designed in 1902 by Alfred Wolff (Cooper, 2003) for the New York Stock Exchange, while Willis Carrier equipped the Sacketts-Wilhems Printing Company with the process AC unit the same year. Coyne College was the first school to offer HVAC training in 1899.[12] The first residential AC was installed by 1914, and by the 1950s there was "widespread adoption of residential AC".[13]

The invention of the components of HVAC systems went hand-in-hand with the Industrial Revolution, and new methods of modernization, higher efficiency, and system control are constantly being introduced by companies and inventors worldwide.

Heating

[edit]

Heaters are appliances whose purpose is to generate heat (i.e. warmth) for the building. This can be done via central heating. Such a system contains a boiler, furnace, or heat pump to heat water, steam, or air in a central location such as a furnace room in a home, or a mechanical room in a large building. The heat can be transferred by convection, conduction, or radiation. Space heaters are used to heat single rooms and only consist of a single unit.

Generation

[edit]
Central heating unit

Heaters exist for various types of fuel, including solid fuels, liquids, and gases. Another type of heat source is electricity, normally heating ribbons composed of high resistance wire (see Nichrome). This principle is also used for baseboard heaters and portable heaters. Electrical heaters are often used as backup or supplemental heat for heat pump systems.

The heat pump gained popularity in the 1950s in Japan and the United States.[14] Heat pumps can extract heat from various sources, such as environmental air, exhaust air from a building, or from the ground. Heat pumps transfer heat from outside the structure into the air inside. Initially, heat pump HVAC systems were only used in moderate climates, but with improvements in low temperature operation and reduced loads due to more efficient homes, they are increasing in popularity in cooler climates. They can also operate in reverse to cool an interior.

Distribution

[edit]

Water/steam

[edit]

In the case of heated water or steam, piping is used to transport the heat to the rooms. Most modern hot water boiler heating systems have a circulator, which is a pump, to move hot water through the distribution system (as opposed to older gravity-fed systems). The heat can be transferred to the surrounding air using radiators, hot water coils (hydro-air), or other heat exchangers. The radiators may be mounted on walls or installed within the floor to produce floor heat.

The use of water as the heat transfer medium is known as hydronics. The heated water can also supply an auxiliary heat exchanger to supply hot water for bathing and washing.

Air

[edit]

Warm air systems distribute the heated air through ductwork systems of supply and return air through metal or fiberglass ducts. Many systems use the same ducts to distribute air cooled by an evaporator coil for air conditioning. The air supply is normally filtered through air filters[dubiousdiscuss] to remove dust and pollen particles.[15]

Dangers

[edit]

The use of furnaces, space heaters, and boilers as a method of indoor heating could result in incomplete combustion and the emission of carbon monoxide, nitrogen oxides, formaldehyde, volatile organic compounds, and other combustion byproducts. Incomplete combustion occurs when there is insufficient oxygen; the inputs are fuels containing various contaminants and the outputs are harmful byproducts, most dangerously carbon monoxide, which is a tasteless and odorless gas with serious adverse health effects.[16]

Without proper ventilation, carbon monoxide can be lethal at concentrations of 1000 ppm (0.1%). However, at several hundred ppm, carbon monoxide exposure induces headaches, fatigue, nausea, and vomiting. Carbon monoxide binds with hemoglobin in the blood, forming carboxyhemoglobin, reducing the blood's ability to transport oxygen. The primary health concerns associated with carbon monoxide exposure are its cardiovascular and neurobehavioral effects. Carbon monoxide can cause atherosclerosis (the hardening of arteries) and can also trigger heart attacks. Neurologically, carbon monoxide exposure reduces hand to eye coordination, vigilance, and continuous performance. It can also affect time discrimination.[17]

Ventilation

[edit]

Ventilation is the process of changing or replacing air in any space to control the temperature or remove any combination of moisture, odors, smoke, heat, dust, airborne bacteria, or carbon dioxide, and to replenish oxygen. It plays a critical role in maintaining a healthy indoor environment by preventing the buildup of harmful pollutants and ensuring the circulation of fresh air. Different methods, such as natural ventilation through windows and mechanical ventilation systems, can be used depending on the building design and air quality needs. Ventilation often refers to the intentional delivery of the outside air to the building indoor space. It is one of the most important factors for maintaining acceptable indoor air quality in buildings.

Although ventilation is an integral component of maintaining good indoor air quality, it may not be satisfactory alone.[18] A clear understanding of both indoor and outdoor air quality parameters is needed to improve the performance of ventilation in terms of ...[19] In scenarios where outdoor pollution would deteriorate indoor air quality, other treatment devices such as filtration may also be necessary.[20]

Methods for ventilating a building may be divided into mechanical/forced and natural types.[21]

Mechanical or forced

[edit]
HVAC ventilation exhaust for a 12-story building
An axial belt-drive exhaust fan serving an underground car park. This exhaust fan's operation is interlocked with the concentration of contaminants emitted by internal combustion engines.

Mechanical, or forced, ventilation is provided by an air handler (AHU) and used to control indoor air quality. Excess humidity, odors, and contaminants can often be controlled via dilution or replacement with outside air. However, in humid climates more energy is required to remove excess moisture from ventilation air.

Kitchens and bathrooms typically have mechanical exhausts to control odors and sometimes humidity. Factors in the design of such systems include the flow rate (which is a function of the fan speed and exhaust vent size) and noise level. Direct drive fans are available for many applications and can reduce maintenance needs.

In summer, ceiling fans and table/floor fans circulate air within a room for the purpose of reducing the perceived temperature by increasing evaporation of perspiration on the skin of the occupants. Because hot air rises, ceiling fans may be used to keep a room warmer in the winter by circulating the warm stratified air from the ceiling to the floor.

Passive

[edit]
Ventilation on the downdraught system, by impulsion, or the 'plenum' principle, applied to schoolrooms (1899)

Natural ventilation is the ventilation of a building with outside air without using fans or other mechanical systems. It can be via operable windows, louvers, or trickle vents when spaces are small and the architecture permits. ASHRAE defined Natural ventilation as the flow of air through open windows, doors, grilles, and other planned building envelope penetrations, and as being driven by natural and/or artificially produced pressure differentials.[1]

Natural ventilation strategies also include cross ventilation, which relies on wind pressure differences on opposite sides of a building. By strategically placing openings, such as windows or vents, on opposing walls, air is channeled through the space to enhance cooling and ventilation. Cross ventilation is most effective when there are clear, unobstructed paths for airflow within the building.

In more complex schemes, warm air is allowed to rise and flow out high building openings to the outside (stack effect), causing cool outside air to be drawn into low building openings. Natural ventilation schemes can use very little energy, but care must be taken to ensure comfort. In warm or humid climates, maintaining thermal comfort solely via natural ventilation might not be possible. Air conditioning systems are used, either as backups or supplements. Air-side economizers also use outside air to condition spaces, but do so using fans, ducts, dampers, and control systems to introduce and distribute cool outdoor air when appropriate.

An important component of natural ventilation is air change rate or air changes per hour: the hourly rate of ventilation divided by the volume of the space. For example, six air changes per hour means an amount of new air, equal to the volume of the space, is added every ten minutes. For human comfort, a minimum of four air changes per hour is typical, though warehouses might have only two. Too high of an air change rate may be uncomfortable, akin to a wind tunnel which has thousands of changes per hour. The highest air change rates are for crowded spaces, bars, night clubs, commercial kitchens at around 30 to 50 air changes per hour.[22]

Room pressure can be either positive or negative with respect to outside the room. Positive pressure occurs when there is more air being supplied than exhausted, and is common to reduce the infiltration of outside contaminants.[23]

Airborne diseases

[edit]

Natural ventilation [24] is a key factor in reducing the spread of airborne illnesses such as tuberculosis, the common cold, influenza, meningitis or COVID-19. Opening doors and windows are good ways to maximize natural ventilation, which would make the risk of airborne contagion much lower than with costly and maintenance-requiring mechanical systems. Old-fashioned clinical areas with high ceilings and large windows provide the greatest protection. Natural ventilation costs little and is maintenance free, and is particularly suited to limited-resource settings and tropical climates, where the burden of TB and institutional TB transmission is highest. In settings where respiratory isolation is difficult and climate permits, windows and doors should be opened to reduce the risk of airborne contagion. Natural ventilation requires little maintenance and is inexpensive.[25]

Natural ventilation is not practical in much of the infrastructure because of climate. This means that the facilities need to have effective mechanical ventilation systems and or use Ceiling Level UV or FAR UV ventilation systems.

Alpha Black Edition - Sirair Air conditioner with UVC (Ultraviolet Germicidal Irradiation)

Ventilation is measured in terms of Air Changes Per Hour (ACH). As of 2023, the CDC recommends that all spaces have a minimum of 5 ACH.[26] For hospital rooms with airborne contagions the CDC recommends a minimum of 12 ACH.[27] The challenges in facility ventilation are public unawareness,[28][29] ineffective government oversight, poor building codes that are based on comfort levels, poor system operations, poor maintenance, and lack of transparency.[30]

UVC or Ultraviolet Germicidal Irradiation is a function used in modern air conditioners which reduces airborne viruses, bacteria, and fungi, through the use of a built-in LED UV light that emits a gentle glow across the evaporator. As the cross-flow fan circulates the room air, any viruses are guided through the sterilization module’s irradiation range, rendering them instantly inactive.[31]

Air conditioning

[edit]

An air conditioning system, or a standalone air conditioner, provides cooling and/or humidity control for all or part of a building. Air conditioned buildings often have sealed windows, because open windows would work against the system intended to maintain constant indoor air conditions. Outside, fresh air is generally drawn into the system by a vent into a mix air chamber for mixing with the space return air. Then the mixture air enters an indoor or outdoor heat exchanger section where the air is to be cooled down, then be guided to the space creating positive air pressure. The percentage of return air made up of fresh air can usually be manipulated by adjusting the opening of this vent. Typical fresh air intake is about 10% of the total supply air.[citation needed]

Air conditioning and refrigeration are provided through the removal of heat. Heat can be removed through radiation, convection, or conduction. The heat transfer medium is a refrigeration system, such as water, air, ice, and chemicals are referred to as refrigerants. A refrigerant is employed either in a heat pump system in which a compressor is used to drive thermodynamic refrigeration cycle, or in a free cooling system that uses pumps to circulate a cool refrigerant (typically water or a glycol mix).

It is imperative that the air conditioning horsepower is sufficient for the area being cooled. Underpowered air conditioning systems will lead to power wastage and inefficient usage. Adequate horsepower is required for any air conditioner installed.

Refrigeration cycle

[edit]
A simple stylized diagram of the refrigeration cycle: 1) condensing coil, 2) expansion valve, 3) evaporating coil, 4) compressor

The refrigeration cycle uses four essential elements to cool, which are compressor, condenser, metering device, and evaporator.

  • At the inlet of a compressor, the refrigerant inside the system is in a low pressure, low temperature, gaseous state. The compressor pumps the refrigerant gas up to high pressure and temperature.
  • From there it enters a heat exchanger (sometimes called a condensing coil or condenser) where it loses heat to the outside, cools, and condenses into its liquid phase.
  • An expansion valve (also called metering device) regulates the refrigerant liquid to flow at the proper rate.
  • The liquid refrigerant is returned to another heat exchanger where it is allowed to evaporate, hence the heat exchanger is often called an evaporating coil or evaporator. As the liquid refrigerant evaporates it absorbs heat from the inside air, returns to the compressor, and repeats the cycle. In the process, heat is absorbed from indoors and transferred outdoors, resulting in cooling of the building.

In variable climates, the system may include a reversing valve that switches from heating in winter to cooling in summer. By reversing the flow of refrigerant, the heat pump refrigeration cycle is changed from cooling to heating or vice versa. This allows a facility to be heated and cooled by a single piece of equipment by the same means, and with the same hardware.

Free cooling

[edit]

Free cooling systems can have very high efficiencies, and are sometimes combined with seasonal thermal energy storage so that the cold of winter can be used for summer air conditioning. Common storage mediums are deep aquifers or a natural underground rock mass accessed via a cluster of small-diameter, heat-exchanger-equipped boreholes. Some systems with small storages are hybrids, using free cooling early in the cooling season, and later employing a heat pump to chill the circulation coming from the storage. The heat pump is added-in because the storage acts as a heat sink when the system is in cooling (as opposed to charging) mode, causing the temperature to gradually increase during the cooling season.

Some systems include an "economizer mode", which is sometimes called a "free-cooling mode". When economizing, the control system will open (fully or partially) the outside air damper and close (fully or partially) the return air damper. This will cause fresh, outside air to be supplied to the system. When the outside air is cooler than the demanded cool air, this will allow the demand to be met without using the mechanical supply of cooling (typically chilled water or a direct expansion "DX" unit), thus saving energy. The control system can compare the temperature of the outside air vs. return air, or it can compare the enthalpy of the air, as is frequently done in climates where humidity is more of an issue. In both cases, the outside air must be less energetic than the return air for the system to enter the economizer mode.

Packaged split system

[edit]

Central, "all-air" air-conditioning systems (or package systems) with a combined outdoor condenser/evaporator unit are often installed in North American residences, offices, and public buildings, but are difficult to retrofit (install in a building that was not designed to receive it) because of the bulky air ducts required.[32] (Minisplit ductless systems are used in these situations.) Outside of North America, packaged systems are only used in limited applications involving large indoor space such as stadiums, theatres or exhibition halls.

An alternative to packaged systems is the use of separate indoor and outdoor coils in split systems. Split systems are preferred and widely used worldwide except in North America. In North America, split systems are most often seen in residential applications, but they are gaining popularity in small commercial buildings. Split systems are used where ductwork is not feasible or where the space conditioning efficiency is of prime concern.[33] The benefits of ductless air conditioning systems include easy installation, no ductwork, greater zonal control, flexibility of control, and quiet operation.[34] In space conditioning, the duct losses can account for 30% of energy consumption.[35] The use of minisplits can result in energy savings in space conditioning as there are no losses associated with ducting.

With the split system, the evaporator coil is connected to a remote condenser unit using refrigerant piping between an indoor and outdoor unit instead of ducting air directly from the outdoor unit. Indoor units with directional vents mount onto walls, suspended from ceilings, or fit into the ceiling. Other indoor units mount inside the ceiling cavity so that short lengths of duct handle air from the indoor unit to vents or diffusers around the rooms.

Split systems are more efficient and the footprint is typically smaller than the package systems. On the other hand, package systems tend to have a slightly lower indoor noise level compared to split systems since the fan motor is located outside.

Dehumidification

[edit]

Dehumidification (air drying) in an air conditioning system is provided by the evaporator. Since the evaporator operates at a temperature below the dew point, moisture in the air condenses on the evaporator coil tubes. This moisture is collected at the bottom of the evaporator in a pan and removed by piping to a central drain or onto the ground outside.

A dehumidifier is an air-conditioner-like device that controls the humidity of a room or building. It is often employed in basements that have a higher relative humidity because of their lower temperature (and propensity for damp floors and walls). In food retailing establishments, large open chiller cabinets are highly effective at dehumidifying the internal air. Conversely, a humidifier increases the humidity of a building.

The HVAC components that dehumidify the ventilation air deserve careful attention because outdoor air constitutes most of the annual humidity load for nearly all buildings.[36]

Humidification

[edit]

Maintenance

[edit]

All modern air conditioning systems, even small window package units, are equipped with internal air filters.[citation needed] These are generally of a lightweight gauze-like material, and must be replaced or washed as conditions warrant. For example, a building in a high dust environment, or a home with furry pets, will need to have the filters changed more often than buildings without these dirt loads. Failure to replace these filters as needed will contribute to a lower heat exchange rate, resulting in wasted energy, shortened equipment life, and higher energy bills; low air flow can result in iced-over evaporator coils, which can completely stop airflow. Additionally, very dirty or plugged filters can cause overheating during a heating cycle, which can result in damage to the system or even fire.

Because an air conditioner moves heat between the indoor coil and the outdoor coil, both must be kept clean. This means that, in addition to replacing the air filter at the evaporator coil, it is also necessary to regularly clean the condenser coil. Failure to keep the condenser clean will eventually result in harm to the compressor because the condenser coil is responsible for discharging both the indoor heat (as picked up by the evaporator) and the heat generated by the electric motor driving the compressor.

Energy efficiency

[edit]

HVAC is significantly responsible for promoting energy efficiency of buildings as the building sector consumes the largest percentage of global energy.[37] Since the 1980s, manufacturers of HVAC equipment have been making an effort to make the systems they manufacture more efficient. This was originally driven by rising energy costs, and has more recently been driven by increased awareness of environmental issues. Additionally, improvements to the HVAC system efficiency can also help increase occupant health and productivity.[38] In the US, the EPA has imposed tighter restrictions over the years. There are several methods for making HVAC systems more efficient.

Heating energy

[edit]

In the past, water heating was more efficient for heating buildings and was the standard in the United States. Today, forced air systems can double for air conditioning and are more popular.

Some benefits of forced air systems, which are now widely used in churches, schools, and high-end residences, are

  • Better air conditioning effects
  • Energy savings of up to 15–20%
  • Even conditioning[citation needed]

A drawback is the installation cost, which can be slightly higher than traditional HVAC systems.

Energy efficiency can be improved even more in central heating systems by introducing zoned heating. This allows a more granular application of heat, similar to non-central heating systems. Zones are controlled by multiple thermostats. In water heating systems the thermostats control zone valves, and in forced air systems they control zone dampers inside the vents which selectively block the flow of air. In this case, the control system is very critical to maintaining a proper temperature.

Forecasting is another method of controlling building heating by calculating the demand for heating energy that should be supplied to the building in each time unit.

Ground source heat pump

[edit]

Ground source, or geothermal, heat pumps are similar to ordinary heat pumps, but instead of transferring heat to or from outside air, they rely on the stable, even temperature of the earth to provide heating and air conditioning. Many regions experience seasonal temperature extremes, which would require large-capacity heating and cooling equipment to heat or cool buildings. For example, a conventional heat pump system used to heat a building in Montana's −57 °C (−70 °F) low temperature or cool a building in the highest temperature ever recorded in the US—57 °C (134 °F) in Death Valley, California, in 1913 would require a large amount of energy due to the extreme difference between inside and outside air temperatures. A metre below the earth's surface, however, the ground remains at a relatively constant temperature. Utilizing this large source of relatively moderate temperature earth, a heating or cooling system's capacity can often be significantly reduced. Although ground temperatures vary according to latitude, at 1.8 metres (6 ft) underground, temperatures generally only range from 7 to 24 °C (45 to 75 °F).

Solar air conditioning

[edit]

Photovoltaic solar panels offer a new way to potentially decrease the operating cost of air conditioning. Traditional air conditioners run using alternating current, and hence, any direct-current solar power needs to be inverted to be compatible with these units. New variable-speed DC-motor units allow solar power to more easily run them since this conversion is unnecessary, and since the motors are tolerant of voltage fluctuations associated with variance in supplied solar power (e.g., due to cloud cover).

Ventilation energy recovery

[edit]

Energy recovery systems sometimes utilize heat recovery ventilation or energy recovery ventilation systems that employ heat exchangers or enthalpy wheels to recover sensible or latent heat from exhausted air. This is done by transfer of energy from the stale air inside the home to the incoming fresh air from outside.

Air conditioning energy

[edit]

The performance of vapor compression refrigeration cycles is limited by thermodynamics.[39] These air conditioning and heat pump devices move heat rather than convert it from one form to another, so thermal efficiencies do not appropriately describe the performance of these devices. The Coefficient of performance (COP) measures performance, but this dimensionless measure has not been adopted. Instead, the Energy Efficiency Ratio (EER) has traditionally been used to characterize the performance of many HVAC systems. EER is the Energy Efficiency Ratio based on a 35 °C (95 °F) outdoor temperature. To more accurately describe the performance of air conditioning equipment over a typical cooling season a modified version of the EER, the Seasonal Energy Efficiency Ratio (SEER), or in Europe the ESEER, is used. SEER ratings are based on seasonal temperature averages instead of a constant 35 °C (95 °F) outdoor temperature. The current industry minimum SEER rating is 14 SEER. Engineers have pointed out some areas where efficiency of the existing hardware could be improved. For example, the fan blades used to move the air are usually stamped from sheet metal, an economical method of manufacture, but as a result they are not aerodynamically efficient. A well-designed blade could reduce the electrical power required to move the air by a third.[40]

Demand-controlled kitchen ventilation

[edit]

Demand-controlled kitchen ventilation (DCKV) is a building controls approach to controlling the volume of kitchen exhaust and supply air in response to the actual cooking loads in a commercial kitchen. Traditional commercial kitchen ventilation systems operate at 100% fan speed independent of the volume of cooking activity and DCKV technology changes that to provide significant fan energy and conditioned air savings. By deploying smart sensing technology, both the exhaust and supply fans can be controlled to capitalize on the affinity laws for motor energy savings, reduce makeup air heating and cooling energy, increasing safety, and reducing ambient kitchen noise levels.[41]

Air filtration and cleaning

[edit]
Air handling unit, used for heating, cooling, and filtering the air

Air cleaning and filtration removes particles, contaminants, vapors and gases from the air. The filtered and cleaned air then is used in heating, ventilation, and air conditioning. Air cleaning and filtration should be taken in account when protecting our building environments.[42] If present, contaminants can come out from the HVAC systems if not removed or filtered properly.

Clean air delivery rate (CADR) is the amount of clean air an air cleaner provides to a room or space. When determining CADR, the amount of airflow in a space is taken into account. For example, an air cleaner with a flow rate of 30 cubic metres (1,000 cu ft) per minute and an efficiency of 50% has a CADR of 15 cubic metres (500 cu ft) per minute. Along with CADR, filtration performance is very important when it comes to the air in our indoor environment. This depends on the size of the particle or fiber, the filter packing density and depth, and the airflow rate.[42]

Circulation of harmful substances

[edit]

Poorly maintained air conditioners/ventilation systems can harbor mold, bacteria, and other contaminants, which are then circulated throughout indoor spaces, contributing to ...[43]

Industry and standards

[edit]

The HVAC industry is a worldwide enterprise, with roles including operation and maintenance, system design and construction, equipment manufacturing and sales, and in education and research. The HVAC industry was historically regulated by the manufacturers of HVAC equipment, but regulating and standards organizations such as HARDI (Heating, Air-conditioning and Refrigeration Distributors International), ASHRAE, SMACNA, ACCA (Air Conditioning Contractors of America), Uniform Mechanical Code, International Mechanical Code, and AMCA have been established to support the industry and encourage high standards and achievement. (UL as an omnibus agency is not specific to the HVAC industry.)

The starting point in carrying out an estimate both for cooling and heating depends on the exterior climate and interior specified conditions. However, before taking up the heat load calculation, it is necessary to find fresh air requirements for each area in detail, as pressurization is an important consideration.

International

[edit]

ISO 16813:2006 is one of the ISO building environment standards.[44] It establishes the general principles of building environment design. It takes into account the need to provide a healthy indoor environment for the occupants as well as the need to protect the environment for future generations and promote collaboration among the various parties involved in building environmental design for sustainability. ISO16813 is applicable to new construction and the retrofit of existing buildings.[45]

The building environmental design standard aims to:[45]

  • provide the constraints concerning sustainability issues from the initial stage of the design process, with building and plant life cycle to be considered together with owning and operating costs from the beginning of the design process;
  • assess the proposed design with rational criteria for indoor air quality, thermal comfort, acoustical comfort, visual comfort, energy efficiency, and HVAC system controls at every stage of the design process;
  • iterate decisions and evaluations of the design throughout the design process.

United States

[edit]

Licensing

[edit]

In the United States, federal licensure is generally handled by EPA certified (for installation and service of HVAC devices).

Many U.S. states have licensing for boiler operation. Some of these are listed as follows:

Finally, some U.S. cities may have additional labor laws that apply to HVAC professionals.

Societies

[edit]

Many HVAC engineers are members of the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE). ASHRAE regularly organizes two annual technical committees and publishes recognized standards for HVAC design, which are updated every four years.[56]

Another popular society is AHRI, which provides regular information on new refrigeration technology, and publishes relevant standards and codes.

Codes

[edit]

Codes such as the UMC and IMC do include much detail on installation requirements, however. Other useful reference materials include items from SMACNA, ACGIH, and technical trade journals.

American design standards are legislated in the Uniform Mechanical Code or International Mechanical Code. In certain states, counties, or cities, either of these codes may be adopted and amended via various legislative processes. These codes are updated and published by the International Association of Plumbing and Mechanical Officials (IAPMO) or the International Code Council (ICC) respectively, on a 3-year code development cycle. Typically, local building permit departments are charged with enforcement of these standards on private and certain public properties.

Technicians

[edit]
HVAC Technician
Occupation
Occupation type
Vocational
Activity sectors
Construction
Description
Education required
Apprenticeship
Related jobs
Carpenter, electrician, plumber, welder

An HVAC technician is a tradesman who specializes in heating, ventilation, air conditioning, and refrigeration. HVAC technicians in the US can receive training through formal training institutions, where most earn associate degrees. Training for HVAC technicians includes classroom lectures and hands-on tasks, and can be followed by an apprenticeship wherein the recent graduate works alongside a professional HVAC technician for a temporary period.[57] HVAC techs who have been trained can also be certified in areas such as air conditioning, heat pumps, gas heating, and commercial refrigeration.

United Kingdom

[edit]

The Chartered Institution of Building Services Engineers is a body that covers the essential Service (systems architecture) that allow buildings to operate. It includes the electrotechnical, heating, ventilating, air conditioning, refrigeration and plumbing industries. To train as a building services engineer, the academic requirements are GCSEs (A-C) / Standard Grades (1-3) in Maths and Science, which are important in measurements, planning and theory. Employers will often want a degree in a branch of engineering, such as building environment engineering, electrical engineering or mechanical engineering. To become a full member of CIBSE, and so also to be registered by the Engineering Council UK as a chartered engineer, engineers must also attain an Honours Degree and a master's degree in a relevant engineering subject.[citation needed] CIBSE publishes several guides to HVAC design relevant to the UK market, and also the Republic of Ireland, Australia, New Zealand and Hong Kong. These guides include various recommended design criteria and standards, some of which are cited within the UK building regulations, and therefore form a legislative requirement for major building services works. The main guides are:

  • Guide A: Environmental Design
  • Guide B: Heating, Ventilating, Air Conditioning and Refrigeration
  • Guide C: Reference Data
  • Guide D: Transportation systems in Buildings
  • Guide E: Fire Safety Engineering
  • Guide F: Energy Efficiency in Buildings
  • Guide G: Public Health Engineering
  • Guide H: Building Control Systems
  • Guide J: Weather, Solar and Illuminance Data
  • Guide K: Electricity in Buildings
  • Guide L: Sustainability
  • Guide M: Maintenance Engineering and Management

Within the construction sector, it is the job of the building services engineer to design and oversee the installation and maintenance of the essential services such as gas, electricity, water, heating and lighting, as well as many others. These all help to make buildings comfortable and healthy places to live and work in. Building Services is part of a sector that has over 51,000 businesses and employs represents 2–3% of the GDP.

Australia

[edit]

The Air Conditioning and Mechanical Contractors Association of Australia (AMCA), Australian Institute of Refrigeration, Air Conditioning and Heating (AIRAH), Australian Refrigeration Mechanical Association and CIBSE are responsible.

Asia

[edit]

Asian architectural temperature-control have different priorities than European methods. For example, Asian heating traditionally focuses on maintaining temperatures of objects such as the floor or furnishings such as Kotatsu tables and directly warming people, as opposed to the Western focus, in modern periods, on designing air systems.

Philippines

[edit]

The Philippine Society of Ventilating, Air Conditioning and Refrigerating Engineers (PSVARE) along with Philippine Society of Mechanical Engineers (PSME) govern on the codes and standards for HVAC / MVAC (MVAC means "mechanical ventilation and air conditioning") in the Philippines.

India

[edit]

The Indian Society of Heating, Refrigerating and Air Conditioning Engineers (ISHRAE) was established to promote the HVAC industry in India. ISHRAE is an associate of ASHRAE. ISHRAE was founded at New Delhi[58] in 1981 and a chapter was started in Bangalore in 1989. Between 1989 & 1993, ISHRAE chapters were formed in all major cities in India.[citation needed]

See also

[edit]

References

[edit]
  1. ^ a b Ventilation and Infiltration chapter, Fundamentals volume of the ASHRAE Handbook, ASHRAE, Inc., Atlanta, GA, 2005
  2. ^ Designer's Guide to Ceiling-Based Air Diffusion, Rock and Zhu, ASHRAE, Inc., New York, 2002
  3. ^ Rezaie, Behnaz; Rosen, Marc A. (2012). "District heating and cooling: Review of technology and potential enhancements". Applied Energy. 93: 2–10. Bibcode:2012ApEn...93....2R. doi:10.1016/j.apenergy.2011.04.020.
  4. ^ Werner S. (2006). ECOHEATCOOL (WP4) Possibilities with more district heating in Europe. Euroheat & Power, Brussels. Archived 2015-09-24 at the Wayback Machine
  5. ^ Dalin P., Rubenhag A. (2006). ECOHEATCOOL (WP5) Possibilities with more district cooling in Europe, final report from the project. Final Rep. Brussels: Euroheat & Power. Archived 2012-10-15 at the Wayback Machine
  6. ^ Nielsen, Jan Erik (2014). Solar District Heating Experiences from Denmark. Energy Systems in the Alps - storage and distribution … Energy Platform Workshop 3, Zurich - 13/2 2014
  7. ^ Wong B., Thornton J. (2013). Integrating Solar & Heat Pumps. Renewable Heat Workshop.
  8. ^ Pauschinger T. (2012). Solar District Heating with Seasonal Thermal Energy Storage in Germany Archived 2016-10-18 at the Wayback Machine. European Sustainable Energy Week, Brussels. 18–22 June 2012.
  9. ^ "How Renewable Energy Is Redefining HVAC | AltEnergyMag". www.altenergymag.com. Retrieved 2020-09-29.
  10. ^ ""Lake Source" Heat Pump System". HVAC-Talk: Heating, Air & Refrigeration Discussion. Retrieved 2020-09-29.
  11. ^ Swenson, S. Don (1995). HVAC: heating, ventilating, and air conditioning. Homewood, Illinois: American Technical Publishers. ISBN 978-0-8269-0675-5.
  12. ^ "History of Heating, Air Conditioning & Refrigeration". Coyne College. Archived from the original on August 28, 2016.
  13. ^ "What is HVAC? A Comprehensive Guide".
  14. ^ Staffell, Iain; Brett, Dan; Brandon, Nigel; Hawkes, Adam (30 May 2014). "A review of domestic heat pumps".
  15. ^ (Alta.), Edmonton. Edmonton's green home guide : you're gonna love green. OCLC 884861834.
  16. ^ Bearg, David W. (1993). Indoor Air Quality and HVAC Systems. New York: Lewis Publishers. pp. 107–112.
  17. ^ Dianat, I.; Nazari, I. "Characteristic of unintentional carbon monoxide poisoning in Northwest Iran-Tabriz". International Journal of Injury Control and Promotion. Retrieved 2011-11-15.
  18. ^ ANSI/ASHRAE Standard 62.1, Ventilation for Acceptable Indoor Air Quality, ASHRAE, Inc., Atlanta, GA, US
  19. ^ Belias, Evangelos; Licina, Dusan (2024). "European residential ventilation: Investigating the impact on health and energy demand". Energy and Buildings. 304. Bibcode:2024EneBu.30413839B. doi:10.1016/j.enbuild.2023.113839.
  20. ^ Belias, Evangelos; Licina, Dusan (2022). "Outdoor PM2. 5 air filtration: optimising indoor air quality and energy". Building & Cities. 3 (1): 186–203. doi:10.5334/bc.153.
  21. ^ Ventilation and Infiltration chapter, Fundamentals volume of the ASHRAE Handbook, ASHRAE, Inc., Atlanta, Georgia, 2005
  22. ^ "Air Change Rates for typical Rooms and Buildings". The Engineering ToolBox. Retrieved 2012-12-12.
  23. ^ Bell, Geoffrey. "Room Air Change Rate". A Design Guide for Energy-Efficient Research Laboratories. Archived from the original on 2011-11-17. Retrieved 2011-11-15.
  24. ^ "Natural Ventilation for Infection Control in Health-Care Settings" (PDF). World Health Organization (WHO), 2009. Retrieved 2021-07-05.
  25. ^ Escombe, A. R.; Oeser, C. C.; Gilman, R. H.; et al. (2007). "Natural ventilation for the prevention of airborne contagion". PLOS Med. 4 (68): e68. doi:10.1371/journal.pmed.0040068. PMC 1808096. PMID 17326709.
  26. ^ Centers For Disease Control and Prevention (CDC) "Improving Ventilation In Buildings". 11 February 2020.
  27. ^ Centers For Disease Control and Prevention (CDC) "Guidelines for Environmental Infection Control in Health-Care Facilities". 22 July 2019.
  28. ^ Dr. Edward A. Nardell Professor of Global Health and Social Medicine, Harvard Medical School "If We're Going to Live With COVID-19, It's Time to Clean Our Indoor Air Properly". Time. February 2022.
  29. ^ "A Paradigm Shift to Combat Indoor Respiratory Infection - 21st century" (PDF). University of Leeds., Morawska, L, Allen, J, Bahnfleth, W et al. (36 more authors) (2021) A paradigm shift to combat indoor respiratory infection. Science, 372 (6543). pp. 689-691. ISSN 0036-8075
  30. ^ Video "Building Ventilation What Everyone Should Know". YouTube. 17 June 2022.
  31. ^ CDC (June 1, 2020). "Center for Disease Control and Prevention, Decontamination and Reuse of Filtering Facepiece Respirators". cdc.gov. Retrieved September 13, 2024.
  32. ^ "What are Air Ducts? The Homeowner's Guide to HVAC Ductwork". Super Tech. Retrieved 2018-05-14.
  33. ^ "Ductless Mini-Split Heat Pumps". U.S. Department of Energy.
  34. ^ "The Pros and Cons of Ductless Mini Split Air Conditioners". Home Reference. 28 July 2018. Retrieved 9 September 2020.
  35. ^ "Ductless Mini-Split Air Conditioners". ENERGY SAVER. Retrieved 29 November 2019.
  36. ^ Moisture Control Guidance for Building Design, Construction and Maintenance. December 2013.
  37. ^ Chenari, B., Dias Carrilho, J. and Gameiro da Silva, M., 2016. Towards sustainable, energy-efficient and healthy ventilation strategies in buildings: A review. Renewable and Sustainable Energy Reviews, 59, pp.1426-1447.
  38. ^ "Sustainable Facilities Tool: HVAC System Overview". sftool.gov. Retrieved 2 July 2014.
  39. ^ "Heating and Air Conditioning". www.nuclear-power.net. Retrieved 2018-02-10.
  40. ^ Keeping cool and green, The Economist 17 July 2010, p. 83
  41. ^ "Technology Profile: Demand Control Kitchen Ventilation (DCKV)" (PDF). Retrieved 2018-12-04.
  42. ^ a b Howard, J (2003), Guidance for Filtration and Air-Cleaning Systems to Protect Building Environments from Airborne Chemical, Biological, or Radiological Attacks, National Institute for Occupational Safety and Health, doi:10.26616/NIOSHPUB2003136, 2003-136
  43. ^ "The Inside Story: A Guide to Indoor Air Quality". 28 August 2014.
  44. ^ ISO. "Building environment standards". www.iso.org. Retrieved 2011-05-14.
  45. ^ a b ISO. "Building environment design—Indoor environment—General principles". Retrieved 14 May 2011.
  46. ^ "010.01.02 Ark. Code R. § 002 - Chapter 13 - Restricted Lifetime License".
  47. ^ "Boiler Professionals Training and Licensing".
  48. ^ "Michigan Boiler Rules".
  49. ^ "Minn. R. 5225.0550 - EXPERIENCE REQUIREMENTS AND DOCUMENTATION FOR LICENSURE AS AN OPERATING ENGINEER".
  50. ^ "Subchapter 24.122.5 - Licensing".
  51. ^ "Chapter 90 - BOILERS, PRESSURE VESSELS, AND REFRIGERATION".
  52. ^ "Article 33.1-14 - North Dakota Boiler Rules".
  53. ^ "Ohio Admin. Code 1301:3-5-10 - Boiler operator and steam engineer experience requirements".
  54. ^ "Subchapter 13 - Licensing of Boiler and Pressure Vessel Service, Repair and/or Installers".
  55. ^ "Or. Admin. R. 918-225-0691 - Boiler, Pressure Vessel and Pressure Piping Installation, Alteration or Repair Licensing Requirements".
  56. ^ "ASHRAE Handbook Online". www.ashrae.org. Retrieved 2020-06-17.
  57. ^ "Heating, Air Conditioning, and Refrigeration Mechanics and Installers : Occupational Outlook Handbook: : U.S. Bureau of Labor Statistics". www.bls.gov. Retrieved 2023-06-22.
  58. ^ "About ISHRAE". ISHRAE. Retrieved 2021-10-11.

Further reading

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[edit]

Media related to Climate control at Wikimedia Commons

Related media at Wikimedia Commons:

 

Geothermal heating

Geothermal heating is the direct use of geothermal energy for some heating applications. Humans have taken advantage of geothermal heat this way since the Paleolithic era. Approximately seventy countries made direct use of a total of 270 PJ of geothermal heating in 2004. As of 2007, 28 GW of geothermal heating capacity is installed around the world, satisfying 0.07% of global primary energy consumption.[1] Thermal efficiency is high since no energy conversion is needed, but capacity factors tend to be low (around 20%) since the heat is mostly needed in the winter.

Geothermal energy originates from the heat retained within the Earth since the original formation of the planet, from radioactive decay of minerals, and from solar energy absorbed at the surface.[2] Most high temperature geothermal heat is harvested in regions close to tectonic plate boundaries where volcanic activity rises close to the surface of the Earth. In these areas, ground and groundwater can be found with temperatures higher than the target temperature of the application. However, even cold ground contains heat. Below 6 metres (20 ft), the undisturbed ground temperature is consistently at the mean annual air temperature,[3] and this heat can be extracted with a ground source heat pump.

Applications

[edit]
Top countries using the most geothermal heating in 2005[4]
Country Production
PJ/yr
Capacity
GW
Capacity
factor
Dominant
applications
China 45.38 3.69 39% bathing
Sweden 43.2 4.2 33% heat pumps
USA 31.24 7.82 13% heat pumps
Turkey 24.84 1.5 53% district heating
Iceland 24.5 1.84 42% district heating
Japan 10.3 0.82 40% bathing (onsens)
Hungary 7.94 0.69 36% spas/greenhouses
Italy 7.55 0.61 39% spas/space heating
New Zealand 7.09 0.31 73% industrial uses
63 others 71 6.8    
Total 273 28 31% space heating
Direct use of geothermal heat by category in 2015 as adapted from John W. Lund [5]
Category GWh/year
Geothermal heat pumps 90,293
Bathing and swimming 33,164
Space heating 24,508
Greenhouse heating 7,407
Aquaculture pond heating 3,322
Industrial uses 2,904
Cooling/snow melting 722
Agriculture drying 564
Others 403
Total 163,287

There are a wide variety of applications for cheap geothermal heat including heating of houses, greenhouses, bathing and swimming or industrial uses. Most applications use geothermal in the form of hot fluids between 50 °C (122 °F) and 150 °C (302 °F). The suitable temperature varies for the different applications. For direct use of geothermal heat, the temperature range for the agricultural sector lies between 25 °C (77 °F) and 90 °C (194 °F), for space heating lies between 50 °C (122 °F) to 100 °C (212 °F).[4] Heat pipes extend the temperature range down to 5 °C (41 °F) as they extract and "amplify" the heat. Geothermal heat exceeding 150 °C (302 °F) is typically used for geothermal power generation.[6]

In 2004 more than half of direct geothermal heat was used for space heating, and a third was used for spas.[1] The remainder was used for a variety of industrial processes, desalination, domestic hot water, and agricultural applications. The cities of Reykjavík and Akureyri pipe hot water from geothermal plants under roads and pavements to melt snow. Geothermal desalination has been demonstrated.

Geothermal systems tend to benefit from economies of scale, so space heating power is often distributed to multiple buildings, sometimes whole communities. This technique, long practiced throughout the world in locations such as Reykjavík, Iceland;[7] Boise, Idaho;[8] and Klamath Falls, Oregon;[9] is known as district heating.[10]

In Europe alone 280 geothermal district heating plants were in operation in 2016 according to the European Geothermal Energy Council (EGEC) with a total capacity of approximately 4.9 GWth.[11]

Extraction

[edit]

Some parts of the world, including substantial portions of the western USA, are underlain by relatively shallow geothermal resources.[12] Similar conditions exist in Iceland, parts of Japan, and other geothermal hot spots around the world. In these areas, water or steam may be captured from natural hot springs and piped directly into radiators or heat exchangers. Alternatively, the heat may come from waste heat supplied by co-generation from a geothermal electrical plant or from deep wells into hot aquifers. Direct geothermal heating is far more efficient than geothermal electricity generation and has less demanding temperature requirements, so it is viable over a large geographical range. If the shallow ground is hot but dry, air or water may be circulated through earth tubes or downhole heat exchangers which act as heat exchangers with the ground.

Steam under pressure from deep geothermal resources is also used to generate electricity from geothermal power. The Iceland Deep Drilling Project struck a pocket of magma at 2,100m. A cemented steelcase was constructed in the hole with a perforation at the bottom close to the magma. The high temperatures and pressure of the magma steam were used to generate 36MW of electricity, making IDDP-1 the world's first magma-enhanced geothermal system.[13]

In areas where the shallow ground is too cold to provide comfort directly, it is still warmer than the winter air. The thermal inertia of the shallow ground retains solar energy accumulated in the summertime, and seasonal variations in ground temperature disappear completely below 10m of depth. That heat can be extracted with a geothermal heat pump more efficiently than it can be generated by conventional furnaces.[10] Geothermal heat pumps are economically viable essentially anywhere in the world.

In theory, geothermal energy (usually cooling) can also be extracted from existing infrastructure, such as municipal water pipes.[14]

Ground-source heat pumps

[edit]

In regions without any high temperature geothermal resources, a ground-source heat pump (GSHP) can provide space heating and space cooling. Like a refrigerator or air conditioner, these systems use a heat pump to force the transfer of heat from the ground to the building. Heat can be extracted from any source, no matter how cold, but a warmer source allows higher efficiency. A ground-source heat pump uses the shallow ground or ground water (typically starting at 10–12 °C or 50–54 °F) as a source of heat, thus taking advantage of its seasonally moderate temperatures.[15] In contrast, an air source heat pump draws heat from the air (colder outside air) and thus requires more energy.

GSHPs circulate a carrier fluid (usually a mixture of water and small amounts of antifreeze) through closed pipe loops buried in the ground. Single-home systems can be "vertical loop field" systems with bore holes 50–400 feet (15–120 m) deep or,[16] if adequate land is available for extensive trenches, a "horizontal loop field" is installed approximately six feet subsurface. As the fluid circulates underground it absorbs heat from the ground and, on its return, the warmed fluid passes through the heat pump which uses electricity to extract heat from the fluid. The re-chilled fluid is sent back into the ground thus continuing the cycle. The heat extracted and that generated by the heat pump appliance as a byproduct is used to heat the house. The addition of the ground heating loop in the energy equation means that significantly more heat can be transferred to a building than if electricity alone had been used directly for heating.

Switching the direction of heat flow, the same system can be used to circulate the cooled water through the house for cooling in the summer months. The heat is exhausted to the relatively cooler ground (or groundwater) rather than delivering it to the hot outside air as an air conditioner does. As a result, the heat is pumped across a larger temperature difference and this leads to higher efficiency and lower energy use.[15]

This technology makes ground source heating economically viable in any geographical location. In 2004, an estimated million ground-source heat pumps with a total capacity of 15 GW extracted 88 PJ of heat energy for space heating. Global ground-source heat pump capacity is growing by 10% annually.[1]

History

[edit]
The oldest known pool fed by a hot spring, built in the Qin dynasty in the 3rd century BC

Hot springs have been used for bathing at least since Paleolithic times.[17] The oldest known spa is a stone pool on China's Mount Li built in the Qin dynasty in the 3rd century BC, at the same site where the Huaqing Chi palace was later built. Geothermal energy supplied channeled district heating for baths and houses in Pompeii around 0 AD.[18] In the first century AD, Romans conquered Aquae Sulis in England and used the hot springs there to feed public baths and underfloor heating.[19] The admission fees for these baths probably represents the first commercial use of geothermal power. A 1,000-year-old hot tub has been located in Iceland, where it was built by one of the island's original settlers.[20] The world's oldest working geothermal district heating system in Chaudes-Aigues, France, has been operating since the 14th century.[4] The earliest industrial exploitation began in 1827 with the use of geyser steam to extract boric acid from volcanic mud in Larderello, Italy.

In 1892, America's first district heating system in Boise, Idaho, was powered directly by geothermal energy, and was soon copied in Klamath Falls, Oregon in 1900. A deep geothermal well was used to heat greenhouses in Boise in 1926, and geysers were used to heat greenhouses in Iceland and Tuscany at about the same time.[21] Charlie Lieb developed the first downhole heat exchanger in 1930 to heat his house. Steam and hot water from the geysers began to be used to heat homes in Iceland in 1943.

By this time, Lord Kelvin had already invented the heat pump in 1852, and Heinrich Zoelly had patented the idea of using it to draw heat from the ground in 1912.[22] But it was not until the late 1940s that the geothermal heat pump was successfully implemented. The earliest one was probably Robert C. Webber's home-made 2.2 kW direct-exchange system, but sources disagree as to the exact timeline of his invention.[22] J. Donald Kroeker designed the first commercial geothermal heat pump to heat the Commonwealth Building (Portland, Oregon) and demonstrated it in 1946.[23][24] Professor Carl Nielsen of Ohio State University built the first residential open loop version in his home in 1948.[25] The technology became popular in Sweden as a result of the 1973 oil crisis, and has been growing slowly in worldwide acceptance since then. The 1979 development of polybutylene pipe greatly augmented the heat pump's economic viability.[23] Since 2000, a compelling body of research has been dedicated to numerically evidence the advantages and efficiency of using CO2, alternative to water, as heat transmission fluid for geothermal energy recovery from enhanced geothermal systems (EGS) where the permeability of the underground source is enhanced by hydrofracturing.[26][27] As of 2004, there are over one million geothermal heat pumps installed worldwide providing 12 GW of thermal capacity.[28] Each year, about 80,000 units are installed in the US and 27,000 in Sweden.[28]

Economics

[edit]
Geothermal drill machine

Geothermal energy is a type of renewable energy that encourages conservation of natural resources. According to the US Environmental Protection Agency, geo-exchange systems save homeowners 30–70 percent in heating costs, and 20–50 percent in cooling costs, compared to conventional systems.[29] Geo-exchange systems also save money because they require much less maintenance. In addition to being highly reliable they are built to last for decades.

Some utilities, such as Kansas City Power and Light, offer special, lower winter rates for geothermal customers, offering even more savings.[15]

Geothermal drilling risks

[edit]
Cracks at the historic Town Hall of Staufen im Breisgau presumed due to damage from geothermal drilling

In geothermal heating projects the underground is penetrated by trenches or drillholes. As with all underground work, projects may cause problems if the geology of the area is poorly understood.

In the spring of 2007 an exploratory geothermal drilling operation was conducted to provide geothermal heat to the town hall of Staufen im Breisgau. After initially sinking a few millimeters, a process called subsidence,[30] the city center has started to rise gradually[31] causing considerable damage to buildings in the city center, affecting numerous historic houses including the town hall. It is hypothesized that the drilling perforated an anhydrite layer bringing high-pressure groundwater to come into contact with the anhydrite, which then began to expand. Currently no end to the rising process is in sight.[32][33][34] Data from the TerraSAR-X radar satellite before and after the changes confirmed the localised nature of the situation:

A geochemical process called anhydrite swelling has been confirmed as the cause of these uplifts. This is a transformation of the mineral anhydrite (anhydrous calcium sulphate) into gypsum (hydrous calcium sulphate). A pre-condition for this transformation is that the anhydrite is in contact with water, which is then stored in its crystalline structure.[35] There are other sources of potential risks, i.e.: cave enlargement or worsening of stability conditions, quality or quantity degradation of groundwater resources, Specific hazard worsening in the case of landslide-prone areas, worsening of rocky mechanical characteristics, soil and water pollution (i.e. due to antifreeze additives or polluting constructive and boring material).[36] The design defined on the base of site-specific geological, hydrogeological and environmental knowledge prevent all these potential risks.

See also

[edit]

References

[edit]
  1. ^ a b c Fridleifsson, Ingvar B.; Bertani, Ruggero; Huenges, Ernst; Lund, John W.; Ragnarsson, Arni; Rybach, Ladislaus (2008-02-11). "The possible role and contribution of geothermal energy to the mitigation of climate change" (PDF). In O. Hohmeyer; T. Trittin (eds.). Proceedings of the IPCC Scoping Meeting on Renewable Energy Sources. Luebeck, Germany. pp. 59–80. Archived from the original (PDF) on 2017-08-08.
  2. ^ Heat Pumps, Energy Management and Conservation Handbook, 2008, pp. 9–3
  3. ^ Mean Annual Air Temperature
  4. ^ a b c Lund, John W. (June 2007), "Characteristics, Development and utilization of geothermal resources" (PDF), Geo-Heat Centre Quarterly Bulletin, vol. 28, no. 2, Klamath Falls, Oregon: Oregon Institute of Technology, pp. 1–9, ISSN 0276-1084, archived from the original (PDF) on 2010-06-17, retrieved 2009-04-16
  5. ^ Lund, John W. (2015-06-05). "Geothermal Resources Worldwide, Direct Heat Utilization of". Encyclopedia of Sustainability and Technology: 1–29. doi:10.1007/978-1-4939-2493-6_305-3. ISBN 978-1-4939-2493-6.
  6. ^ Hanania, Jordan; Sheardown, Ashley; Stenhouse, Kailyn; Donev, Jason. "Geothermal district heating". Energy education by Prof. Jason Donev and students, University of Calgary. Retrieved 2020-09-18.
  7. ^ "History of the utilization of geothermal sources of energy in Iceland". University of Rochester. Archived from the original on 2012-02-06.
  8. ^ "District Heating Systems in Idaho". Idaho Department of Water Resources. Archived from the original on 2007-01-21.
  9. ^ Brown, Brian.Klamath Falls Geothermal District Heating Systems Archived 2008-01-19 at the Wayback Machine
  10. ^ a b "Geothermal Basics Overview". Office of Energy Efficiency and Renewable Energy. Archived from the original on 2008-10-04. Retrieved 2008-10-01.
  11. ^ "EGEC Geothermal Market Report 2016 Key Findings (Sixth Edition, May 2017)" (PDF). www.egec.org. EGEC - European Geothermal Energy Council. 2017-12-13. p. 9.
  12. ^ What is Geothermal? Archived October 5, 2013, at the Wayback Machine
  13. ^ Wilfred Allan Elders, Guðmundur Ómar Friðleifsson and Bjarni Pálsson (2014). Geothermics Magazine, Vol. 49 (January 2014). Elsevier Ltd.
  14. ^ Tadayon, Saied; Tadayon, Bijan; Martin, David (2012-10-11). "Patent US20120255706 - Heat Exchange Using Underground Water System".
  15. ^ a b c Goswami, Yogi D., Kreith, Frank, Johnson, Katherine (2008), p. 9-4.
  16. ^ "Geothermal Heating and Cooling Systems". Well Management. Minnesota Department of Health. Archived from the original on 2014-02-03. Retrieved 2012-08-25.
  17. ^ Cataldi, Raffaele (August 1993). "Review of historiographic aspects of geothermal energy in the Mediterranean and Mesoamerican areas prior to the Modern Age" (PDF). Geo-Heat Centre Quarterly Bulletin. 15 (1): 13–16. ISSN 0276-1084. Archived from the original (PDF) on 2010-06-18. Retrieved 2009-11-01.
  18. ^ Bloomquist, R. Gordon (2001). Geothermal District Energy System Analysis, Design, and Development (PDF). International Summer School. International Geothermal Association. p. 213(1). Retrieved November 28, 2015. During Roman times, warm water was circulated through open trenches to provide heating for buildings and baths in Pompeii.
  19. ^ "A History of Geothermal Energy in the United States". US Department of Energy, Geothermal Technologies Program. Archived from the original on 2007-09-04. Retrieved 2007-09-10.
  20. ^ "One Hot Island: Iceland's Renewable Geothermal Power". Scientific American.
  21. ^ Dickson, Mary H.; Fanelli, Mario (February 2004). "What is Geothermal Energy?". Pisa, Italy: Istituto di Geoscienze e Georisorse. Archived from the original on 2009-10-09. Retrieved 2009-10-13.
  22. ^ a b Zogg, M. (20–22 May 2008). History of Heat Pumps: Swiss Contributions and International Milestones (PDF). Zürich, Switzerland: 9th International IEA Heat Pump Conference.
  23. ^ a b Bloomquist, R. Gordon (December 1999). "Geothermal Heat Pumps, Four Plus Decades of Experience" (PDF). Geo-Heat Centre Quarterly Bulletin. 20 (4): 13–18. ISSN 0276-1084. Archived from the original (PDF) on 2012-10-31. Retrieved 2009-03-21.
  24. ^ Kroeker, J. Donald; Chewning, Ray C. (February 1948). "A Heat Pump in an Office Building". ASHVE Transactions. 54: 221–238.
  25. ^ Gannon, Robert (February 1978). "Ground-Water Heat Pumps – Home Heating and Cooling from Your Own Well". Popular Science. 212 (2): 78–82. ISSN 0161-7370. Retrieved 2009-11-01.
  26. ^ Brown, D.W. (January 2000). "A Hot Dry Rock Geothermal Energy Concept Utilizing Supercritical CO2 Instead of Water" (PDF). Proceedings of Twenty-Fifth Workshop on Geothermal Reservoir Engineering Stanford University, Stanford, California, January 24-26, 2000: 233–238.
  27. ^ Atrens, A.D.; Gurgenci, H.; Rudolph, V. (2009). "CO2 Thermosiphon for Competitive Geothermal Power Generation". Energy Fuels. 23 (1): 553–557. doi:10.1021/ef800601z.
  28. ^ a b Lund, J.; Sanner, B.; Rybach, L.; Curtis, R.; Hellström, G. (September 2004). "Geothermal (Ground Source) Heat Pumps, A World Overview" (PDF). Geo-Heat Centre Quarterly Bulletin. 25 (3): 1–10. ISSN 0276-1084. Archived from the original (PDF) on 2014-02-01. Retrieved 2009-03-21.
  29. ^ "Geothermal Heat Pump Consortium, Inc". Retrieved 2008-04-27.
  30. ^ The Telegraph: Geothermal probe sinks German city (March 31, 2008)
  31. ^ Lubbadeh, Jens (15 November 2008). "Eine Stadt zerreißt" [A town rips up]. Spiegel Wissenschaft (in German). Partial translation.
  32. ^ Sass, Ingo; Burbaum, Ulrich (2010). "Damage to the historic town of Staufen (Germany) caused by geothermal drillings through anhydrite-bearing formations". Acta Carsologica. 39 (2): 233. doi:10.3986/ac.v39i2.96.
  33. ^ Butscher, Christoph; Huggenberger, Peter; Auckenthaler, Adrian; Bänninger, Dominik (2010). "Risikoorientierte Bewilligung von Erdwärmesonden" (PDF). Grundwasser. 16 (1): 13–24. Bibcode:2011Grund..16...13B. doi:10.1007/s00767-010-0154-5. S2CID 129598890.
  34. ^ Goldscheider, Nico; Bechtel, Timothy D. (2009). "Editors' message: The housing crisis from underground—damage to a historic town by geothermal drillings through anhydrite, Staufen, Germany". Hydrogeology Journal. 17 (3): 491–493. Bibcode:2009HydJ...17..491G. doi:10.1007/s10040-009-0458-7.
  35. ^ "TerraSAR-X Image Of The Month: Ground Uplift Under Staufen's Old Town". www.spacemart.com. SpaceDaily. 2009-10-22. Retrieved 2009-10-23.
  36. ^ De Giorgio, Giorgio; Chieco, Michele; Limoni, Pier Paolo; Zuffianò, Livia Emanuela; Dragone, Vittoria; Romanazzi, Annarita; Pagliarulo, Rossella; Musicco, Giuseppe; Polemio, Maurizio (2020-10-19). "Improving Regulation and the Role of Natural Risk Knowledge to Promote Sustainable Low Enthalpy Geothermal Energy Utilization". Water. 12 (10): 2925. doi:10.3390/w12102925. ISSN 2073-4441.
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Electrical troubleshooting helps by systematically checking the HVAC systems components for voltage, current, and resistance issues. It identifies faulty wiring, defective sensors, or malfunctioning control boards that might not be immediately apparent but can lead to inefficiencies or failures.
Common electrical issues include blown fuses, tripped circuit breakers, loose connections, and faulty capacitors. These problems can cause the air conditioner to stop working entirely or run inefficiently, leading to inadequate cooling or increased energy consumption.
Using specialized tools like multimeters and oscilloscopes allows technicians to accurately diagnose electrical faults without causing further damage. These tools provide precise measurements needed to identify issues such as short circuits or open circuits within the complex wiring of an HVAC system.