Why AC Tune Ups Are Essential for Summer Cooling

radiant heating systems

As summer approaches, homeowners and facility managers alike turn their attention to ensuring that air conditioning systems are ready to tackle the sweltering heat. In this context, the concept of preventative maintenance takes center stage, underscoring the importance of regular AC tune-ups. Not only do these tune-ups ensure optimal cooling performance during peak summer months, but they also offer significant cost savings in both immediate and long-term scenarios.


Preventative maintenance involves a proactive approach to caring for your air conditioning system. By scheduling regular tune-ups before the onset of warmer weather, you can identify and address potential issues that could impede performance or lead to breakdowns. During a typical AC tune-up, technicians inspect critical components such as coils, filters, refrigerant levels, and electrical connections. They clean and lubricate parts as necessary, ensuring that the system operates at peak efficiency.


Seasonal weather changes can impact performance, making Emergency AC repair it’s important to schedule repairs as soon as possible..

The benefits of this proactive care are manifold. For one, an efficiently running AC unit consumes less energy. This translates directly into lower utility bills throughout the summer months when cooling demands are highest. Furthermore, by identifying potential problems early through regular maintenance checks, you reduce the risk of unexpected breakdowns that could result in costly emergency repairs or even full system replacements.


Beyond immediate cost savings on energy bills and repair costs, preventative maintenance also extends the lifespan of your AC system. A well-maintained unit is less prone to wear and tear over time. This longevity means homeowners can defer the substantial investment required for a new system installation by several years-a significant financial advantage.


Moreover, maintaining an efficient air conditioning system contributes positively to environmental sustainability efforts by reducing energy consumption and minimizing greenhouse gas emissions associated with excessive electricity use.


In conclusion, investing in regular AC tune-ups is not merely about comfort during summer's intense heat; it's about embracing a strategy that combines preventative maintenance with tangible cost savings. By ensuring your cooling system runs effectively and efficiently through routine care, you protect your wallet from unexpected expenses while simultaneously contributing to a more sustainable environment-a win-win scenario for everyone involved.

Preventative Maintenance and Cost Savings

Enhancing Energy Efficiency and Reducing Utility Bills

As the sweltering days of summer approach, ensuring that your air conditioning system is running efficiently becomes a priority for many homeowners. The rising temperatures are not just uncomfortable; they can also result in soaring utility bills if your AC unit is not performing optimally. This is where the importance of an annual AC tune-up comes into play, offering both enhanced energy efficiency and reduced utility costs.


An air conditioner, much like any other machine, requires regular maintenance to function at its best. Over time, components such as filters, coils, and fins accumulate dust and debris, which can impede airflow and reduce efficiency. A professional tune-up involves cleaning these parts thoroughly, ensuring that your system runs smoothly. When an AC unit operates with clean components and unobstructed airflow, it uses less energy to cool your home. This enhanced efficiency directly translates into lower energy consumption and subsequently reduced utility bills.


Moreover, an AC tune-up helps identify potential issues before they escalate into costly repairs or replacements. Technicians can spot signs of wear and tear or detect failing parts during routine maintenance checks. Addressing these minor problems early on ensures that your system remains reliable throughout the peak cooling season. This preventive measure not only saves money by avoiding expensive breakdowns but also extends the lifespan of your AC unit.


In addition to financial savings, maintaining an efficient air conditioning system has environmental benefits. Energy-efficient systems consume less electricity, reducing greenhouse gas emissions associated with energy production. By optimizing your AC's performance through regular tune-ups, you contribute positively to efforts aimed at combating climate change.


Furthermore, a well-maintained air conditioner provides better indoor air quality and comfort levels within your home. Clean filters and coils mean fewer allergens circulating in the air you breathe-a significant advantage for those who suffer from allergies or respiratory issues.


In conclusion, scheduling a professional AC tune-up before summer sets in is essential for several reasons: it enhances the energy efficiency of your cooling system; it reduces utility bills by lowering energy consumption; it prevents costly repairs by detecting potential issues early; it contributes to environmental sustainability; and it improves overall indoor comfort and air quality. As temperatures rise, ensuring that your air conditioning system is ready to handle the heat will provide peace of mind while keeping both you and your wallet cool throughout the season.

Extending the Lifespan of Your Air Conditioning Unit

As the sweltering summer months approach, many of us find solace in the cool comfort provided by our air conditioning units. However, just as we prepare ourselves for the heat with lighter clothing and sunscreen, our AC systems also require a bit of preparation to ensure they function optimally throughout the season. This is where regular AC tune-ups come into play, serving as a crucial measure not only for immediate comfort but also for extending the lifespan of your air conditioning unit.


An air conditioning unit is a significant investment for any household or business. Like any mechanical system, it comprises various components that can wear down over time due to usage and environmental factors. A routine tune-up involves a comprehensive checkup that ensures each component of your AC is in good working order. This includes cleaning or replacing filters, checking refrigerant levels, inspecting electrical connections, and ensuring the thermostat functions correctly. Addressing these aspects before they become problematic can significantly reduce the risk of unexpected breakdowns during peak heat times.


Moreover, regular maintenance helps enhance energy efficiency which directly impacts utility bills. Over time, dust and debris accumulate within an AC unit's components, forcing it to work harder to cool your space effectively.

Why AC Tune Ups Are Essential for Summer Cooling - energy efficiency upgrades

  1. HVAC duct sealing
  2. HVAC system retrofitting
  3. variable refrigerant flow (VRF) systems
This not only increases energy consumption but also accelerates wear and tear on critical parts of the system. A professional tune-up cleans and clears these obstructions, optimizing performance and reducing energy waste.


Another compelling reason for scheduling regular AC maintenance lies in its ability to extend the lifespan of your unit. Just as regular oil changes keep a car running smoothly for years, periodic AC tune-ups address minor issues before they grow into major problems that could necessitate costly repairs or even replacement of the entire unit. By investing in routine care now, you're effectively prolonging your system's life expectancy while avoiding larger expenses down the road.


Furthermore, an efficiently running air conditioner contributes positively to indoor air quality-a vital consideration as we spend more time indoors during extreme weather conditions. Clean filters and ducts mean fewer allergens and pollutants circulating through your home or office space; this creates a healthier environment overall.


In conclusion, prioritizing annual or biannual air conditioning tune-ups offers multiple benefits: enhanced performance during hot months when demand is highest; lowered utility costs thanks to improved efficiency; prolonged equipment longevity saving money long-term; plus better indoor air quality contributing positively towards occupant health standards too! So remember - taking proactive steps today ensures uninterrupted comfort tomorrow!

Extending the Lifespan of Your Air Conditioning Unit
Improving Indoor Air Quality and Comfort Levels

Improving Indoor Air Quality and Comfort Levels

As the summer sun begins to blaze, our homes transform into sanctuaries of cool relief, thanks in large part to the indispensable air conditioning systems that hum quietly in the background. However, ensuring these systems operate optimally is critical—not just for maintaining comfort but also for improving indoor air quality. This is where regular AC tune-ups play a pivotal role, proving essential for a refreshing and healthy summer experience.


Air conditioners are intricate machines composed of various components working in harmony to provide cool air. Over time, these components can suffer from wear and tear or accumulate dust and debris, which can hinder their efficiency. A comprehensive AC tune-up involves cleaning and inspecting these parts—such as coils, filters, and fins—to ensure they function correctly. When an air conditioner runs efficiently, it not only keeps energy bills manageable but also maintains a consistent temperature throughout your home, enhancing your overall comfort levels.




Why AC Tune Ups Are Essential for Summer Cooling - compressor troubleshooting

  1. HVAC installation
  2. duct cleaning
  3. climate control systems

More importantly, regular maintenance directly impacts indoor air quality. Air conditioners do more than just cool; they circulate air throughout the living spaces. If filters are clogged or if there is a buildup of mold or bacteria within the system due to neglect, these contaminants can be dispersed throughout your home. An AC tune-up includes replacing or cleaning filters and checking for any signs of moisture accumulation where mold might thrive. By addressing these issues proactively through professional maintenance services, you significantly reduce the risk of circulating allergens or pollutants indoors.


Additionally, well-maintained air conditioning systems help manage humidity levels within the home. High humidity can make even moderately warm temperatures feel uncomfortable and sticky while also promoting mold growth and dust mite populations—common triggers for allergies and asthma. By keeping your AC in top shape through regular tune-ups, you ensure it effectively dehumidifies your living space alongside cooling it down.


In essence, investing in routine AC tune-ups before the peak summer months isn't merely about avoiding inconvenient breakdowns—it’s about creating a healthier living environment that prioritizes both comfort and well-being. These check-ups extend the lifespan of your unit while fostering better indoor air quality by eliminating potential sources of pollution right at their origin.


Therefore, as we prepare to embrace another season under bright sunny skies with rising temperatures outdoors, let us remember that keeping our cooling systems serviced goes beyond immediate gratification; it's an investment towards long-term health benefits within our homes too—a decision every homeowner should consider essential each year without hesitation.

Identifying Potential Problems Early to Avoid Major Repairs

As the sweltering days of summer approach, many homeowners are reminded of the indispensable role their air conditioning systems play in providing relief from the heat. However, one often overlooked aspect of maintaining a comfortable home environment is the importance of regular AC tune-ups. Identifying potential problems early through routine maintenance can be crucial in avoiding major repairs and ensuring your cooling system operates efficiently throughout the hottest months.


When an air conditioner is running smoothly, it's easy to take it for granted. Yet, like any complex machine, an AC unit comprises numerous components that can wear out over time. Filters become clogged with dust and debris, refrigerant levels fluctuate, and electrical connections may loosen or corrode. Each of these seemingly minor issues has the potential to escalate into significant problems if left unchecked.


This is where regular AC tune-ups come into play. By scheduling a professional inspection before the peak summer season begins, you allow a trained technician to thoroughly assess your system. They will clean or replace dirty filters, check refrigerant levels, inspect electrical connections, and lubricate moving parts if necessary. This proactive approach not only enhances performance but also extends the lifespan of your unit.


One key advantage of early problem detection during an AC tune-up is that it often results in cost savings. Minor repairs identified during routine maintenance are typically less expensive than emergency fixes required when a system breaks down unexpectedly during a heatwave. For example, replacing a worn-out fan belt or fixing a small refrigerant leak before they lead to compressor failure can save homeowners from hefty repair bills.


Moreover, addressing potential issues early contributes significantly to energy efficiency. An air conditioning system burdened with unresolved maintenance problems requires more energy to achieve desired cooling levels. This inefficiency translates into higher utility bills-a burden most would prefer to avoid.


Beyond financial considerations, there's also an environmental aspect to consider. A well-maintained AC unit consumes less electricity and reduces greenhouse gas emissions associated with power generation. Thus, by prioritizing regular tune-ups and preventing larger mechanical failures through early intervention, homeowners contribute positively to environmental conservation efforts.


Finally, peace of mind is another intangible yet valuable benefit afforded by identifying potential problems early through AC tune-ups. Knowing that your cooling system is primed for optimal performance allows you to enjoy summer without worrying about unexpected breakdowns disrupting your comfort at home.


In conclusion, while it might be tempting to postpone or even skip annual air conditioning maintenance appointments altogether-especially when everything seems fine-it's essential not only for immediate comfort but also long-term savings and sustainability concerns that we prioritize these routine checks regularly each year prior summertime arrives full force upon us once again!

Identifying Potential Problems Early to Avoid Major Repairs
Ensuring Reliable Performance During Peak Summer Months
Ensuring Reliable Performance During Peak Summer Months

As the summer months approach, the anticipation of warm weather is often accompanied by a familiar concern: the reliability of our air conditioning systems. While many homeowners may overlook the necessity of regular maintenance, ensuring reliable performance during peak summer months is crucial. An AC tune-up, much like a physical check-up for our bodies, is essential for keeping your cooling system in optimal condition and preventing any unwelcome surprises when temperatures soar.


Firstly, an annual AC tune-up enhances efficiency. Over time, dust and debris can accumulate within the system, obstructing airflow and making it work harder to cool your home. This not only results in increased energy consumption but also escalates utility bills. A professional technician will clean critical components such as coils and filters during a tune-up, ensuring that your AC runs smoothly and efficiently throughout the summer.


Moreover, regular maintenance extends the lifespan of your air conditioning unit. Just as neglecting oil changes can lead to engine trouble in a car, ignoring routine AC maintenance can result in costly repairs or even premature system failure. By addressing minor issues before they become major problems, you are safeguarding your investment and potentially saving substantial amounts on unexpected repair costs.


Another significant benefit of AC tune-ups is improved indoor air quality. As part of the service, technicians will inspect and replace filters if needed. Clean filters trap dust, allergens, and other pollutants more effectively, contributing to healthier indoor air—a particularly important consideration for families with members who suffer from allergies or respiratory conditions.


Furthermore, an AC tune-up enhances comfort by ensuring consistent cooling performance. There's nothing worse than enduring sweltering heat due to an underperforming air conditioner during a heatwave. Regular inspections help identify wear-and-tear issues that could compromise your unit's ability to distribute cool air evenly throughout your home.


Finally, timely maintenance provides peace of mind by reducing the likelihood of inconvenient breakdowns when they're least expected—typically during those scorching days when demand for professional services peaks and appointment availability becomes scarce.


In conclusion, investing in an annual AC tune-up is not merely about maintaining comfort; it’s about guaranteeing seamless operation when you need it most—during peak summer months.

Why AC Tune Ups Are Essential for Summer Cooling - energy efficiency upgrades

  1. radiant heating systems
  2. compressor troubleshooting
  3. energy efficiency upgrades
As Benjamin Franklin wisely stated: "An ounce of prevention is worth a pound of cure." By taking proactive measures now through regular maintenance checks with qualified professionals—you ensure reliable performance while maximizing efficiency—and ultimately enjoy peace-of-mind knowing that refreshing relief from oppressive heat awaits inside no matter how high external temperatures climb outside!

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.
[edit]

 

 

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
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Regular AC tune-ups ensure that all components of the system are clean and functioning properly, which reduces strain on the unit. This leads to more efficient operation, lower energy consumption, and reduced utility bills during hot summer months.
An AC tune-up can identify and address minor issues such as refrigerant leaks, worn-out parts, or clogged filters before they lead to major breakdowns. This proactive maintenance helps prevent unexpected failures when you need your cooling system the most.
It is recommended to schedule an AC tune-up at least once a year, ideally in the spring before temperatures rise. This ensures your system is in peak condition to handle increased demand during the summer months.