This article is about cooling of air. For the Curved Air album, seeAir Conditioning (album). For a similar device capable of both cooling and heating, seeheat pump.
"a/c" redirects here. For the abbreviation used in banking and book-keeping, seeAccount (disambiguation). For other uses, seeAC.
There are various types of air conditioners. Popular examples include: Window-mounted air conditioner (China, 2023); Ceiling-mounted cassette air conditioner (China, 2023); Wall-mounted air conditioner (Japan, 2020); Ceiling-mounted console (Also called ceiling suspended) air conditioner (China, 2023); and portable air conditioner (Vatican City, 2018).
Air conditioning, often abbreviated asA/C (US) orair con (UK),[1] is the process of removingheat from an enclosed space to achieve a more comfortable interior temperature and in some cases also controlling thehumidity of internal air. Air conditioning can be achieved using a mechanical 'air conditioner' or by other methods, includingpassive cooling andventilative cooling.[2][3] Air conditioning is a member of a family of systems and techniques that provideheating, ventilation, and air conditioning (HVAC).[4]Heat pumps are similar in many ways to air conditioners, but use areversing valve to allow them both to heat and to cool an enclosed space.[5]
Air conditioners, which typically usevapor-compression refrigeration, range in size from small units used in vehicles or single rooms to massive units that can cool large buildings.[6]Air source heat pumps, which can be used for heating as well ascooling, are becoming increasingly common in cooler climates.
Air conditioning dates back to prehistory.[9] Double-walled living quarters, with a gap between the two walls to encourage air flow, were found in the ancient city ofHamoukar, in modernSyria.[10]Ancient Egyptian buildings also used a wide variety of passive air-conditioning techniques.[11] These became widespread from theIberian Peninsula through North Africa, the Middle East, and Northern India.[12]
Passive techniques remained widespread until the 20th century when they fell out of fashion and were replaced by powered air conditioning. Using information from engineering studies of traditional buildings, passive techniques are being revived and modified for 21st-century architectural designs.[13][12]
An array of air conditioner condenser units outside a commercial office building
Air conditioners allow the building's indoor environment to remain relatively constant, largely independent of changes in external weather conditions and internal heat loads. They also enabledeep plan buildings to be created and have allowed people to live comfortably in hotter parts of the world.[14]
In 1558,Giambattista della Porta described a method of chilling ice totemperatures far below itsfreezing point by mixing it withpotassium nitrate (then called "nitre") in hispopular science bookNatural Magic.[15][16][17] In 1620,Cornelis Drebbel demonstrated "Turning Summer into Winter" forJames I of England, chilling part of the Great Hall ofWestminster Abbey with an apparatus of troughs and vats.[18] Drebbel's contemporaryFrancis Bacon, like della Porta a believer inscience communication, may not have been present at the demonstration, but in a book published later the same year, he described it as "experiment of artificial freezing" and said that "Nitre (or rather its spirit) is very cold, and hence nitre or salt when added to snow or ice intensifies the cold of the latter, the nitre by adding to its cold, but the salt by supplying activity to the cold of the snow."[15]
In 1758,Benjamin Franklin andJohn Hadley, a chemistry professor at theUniversity of Cambridge, conducted experiments applying the principle of evaporation as a means to cool an object rapidly. Franklin and Hadley confirmed that the evaporation of highlyvolatile liquids (such asalcohol andether) could be used to drive down the temperature of an object past the freezing point of water. They experimented with the bulb of amercury-in-glass thermometer as their object. They used a bellows to speed up theevaporation. They lowered the temperature of the thermometer bulb down to −14 °C (7 °F) while the ambient temperature was 18 °C (64 °F). Franklin noted that soon after they passed the freezing point of water 0 °C (32 °F), a thin film of ice formed on the surface of the thermometer's bulb and that the ice mass was about 6 mm (1⁄4 in) thick when they stopped the experiment upon reaching −14 °C (7 °F). Franklin concluded: "From this experiment, one may see the possibility of freezing a man to death on a warm summer's day."[19]
The 19th century included many developments in compression technology. In 1820, English scientist and inventorMichael Faraday discovered that compressing and liquefyingammonia could chill air when the liquefied ammonia was allowed to evaporate.[20] In 1842, Florida physicianJohn Gorrie used compressor technology to create ice, which he used to cool air for his patients in his hospital inApalachicola, Florida. He hoped to eventually use his ice-making machine to regulate the temperature of buildings.[20][21] He envisioned centralized air conditioning that could cool entire cities. Gorrie was granted a patent in 1851,[22] but following the death of his main backer, he was not able to realize his invention.[23] In 1851,James Harrison created the first mechanical ice-making machine inGeelong, Australia, and was granted a patent for an ethervapor-compression refrigeration system in 1855 that produced three tons of ice per day.[24] In 1860, Harrison established a second ice company. He later entered the debate over competing against the American advantage of ice-refrigerated beef sales to the United Kingdom.[24]
Willis Carrier, who is credited with building the first modern electrical air conditioning unit
Electricity made the development of effective units possible. In 1901, American inventorWillis H. Carrier built what is considered the first modern electrical air conditioning unit.[25][26][27][28] In 1902, he installed his first air-conditioning system, in the Sackett-Wilhelms Lithographing & Publishing Company inBrooklyn, New York.[29] His invention controlled both the temperature and humidity, which helped maintain consistent paper dimensions and ink alignment at the printing plant. Later, together with six other employees, Carrier formedThe Carrier Air Conditioning Company of America, a business that in 2020 employed 53,000 people and was valued at $18.6 billion.[30][31]
In 1906,Stuart W. Cramer ofCharlotte, North Carolina, was exploring ways to addmoisture to the air in his textile mill. Cramer coined the term "air conditioning" in a patent claim which he filed that year, where he suggested that air conditioning was analogous to "water conditioning", then a well-known process for making textiles easier to process.[32] He combined moisture with ventilation to "condition" and change the air in the factories; thus, controlling the humidity that is necessary in textile plants. Willis Carrier adopted the term and incorporated it into the name of his company.[33]
Domestic air conditioning soon took off. In 1914, the first domestic air conditioning was installed inMinneapolis in the home ofCharles Gilbert Gates. It is, however, possible that the considerable device (c. 2.1 m × 1.8 m × 6.1 m; 7 ft × 6 ft × 20 ft) was never used, as the house remained uninhabited[20] (Gates had already died in October 1913.)
In 1931, H.H. Schultz and J.Q. Sherman developed what would become the most common type of individual room air conditioner: one designed to sit on a window ledge. The units went on sale in 1932 at US$10,000 to $50,000 (the equivalent of $200,000 to $1,200,000 in 2024.)[20] A year later, the firstair conditioning systems for cars were offered for sale.[34]Chrysler Motors introduced the first practical semi-portable air conditioning unit in 1935,[35] andPackard became the first automobile manufacturer to offer an air conditioning unit in its cars in 1939.[36]
Innovations in the latter half of the 20th century allowed more ubiquitous air conditioner use. In 1945, Robert Sherman ofLynn, Massachusetts, invented a portable, in-window air conditioner that cooled, heated, humidified, dehumidified, and filtered the air.[37] The first inverter air conditioners were released in 1980–1981.[38][39]
In 1954, Ned Cole, a 1939 architecture graduate from theUniversity of Texas at Austin, developed the first experimental "suburb" with inbuilt air conditioning in each house. 22 homes were developed on a flat, treeless track in northwestAustin, Texas, and the community was christened the 'Austin Air-Conditioned Village.' The residents were subjected to a year-long study of the effects of air conditioning led by the nation’s premier air conditioning companies, builders, and social scientists. In addition, researchers from UT’s Health Service and Psychology Department studied the effects on the "artificially cooled humans." One of the more amusing discoveries was that each family reported being troubled with scorpions, the leading theory being that scorpions sought cool, shady places. Other reported changes in lifestyle were that mothers baked more, families ate heavier foods, and they were more apt to choose hot drinks.[40][41]
Air conditioner adoption tends to increase above around $10,000 annual household income in warmer areas.[42] GlobalGDP growth explains around 85% of increased air condition adoption by 2050, while the remaining 15% can be explained byclimate change.[42]
As of 2016 an estimated 1.6 billion air conditioning units were used worldwide, with over half of them inChina andUSA, and a total cooling capacity of 11,675 gigawatts.[8][43] TheInternational Energy Agency predicted in 2018 that the number of air conditioning units would grow to around 4 billion units by 2050 and that the total cooling capacity would grow to around 23,000 GW, with the biggest increases inIndia andChina.[8] Between 1995 and 2004, the proportion of urban households in China with air conditioners increased from 8% to 70%.[44] As of 2015, nearly 100 million homes, or about 87% of US households, had air conditioning systems.[45] In 2019, it was estimated that 90% of new single-family homes constructed in the US included air conditioning (ranging from 99% in theSouth to 62% in theWest).[46][47]
Cooling in traditional air conditioner systems is accomplished using the vapor-compression cycle, which uses a refrigerant's forced circulation andphase change between gas andliquid to transfer heat.[48][49] The vapor-compression cycle can occur within a unitary, or packaged piece of equipment; or within a chiller that is connected to terminal cooling equipment (such as a fan coil unit in an air handler) on its evaporator side and heat rejection equipment such as a cooling tower on its condenser side. Anair source heat pump shares many components with an air conditioning system, but includes areversing valve, which allows the unit to be used to heat as well as cool a space.[50]
Air conditioning equipment will reduce the absolute humidity of the air processed by the system if the surface of the evaporator coil is significantly cooler than thedew point of the surrounding air. An air conditioner designed for an occupied space will typically achieve a 30% to 60% relative humidity in the occupied space.[51]
Most modern air-conditioning systems feature a dehumidification cycle during which the compressor runs. At the same time, the fan is slowed to reduce the evaporator temperature and condense more water. Adehumidifier uses the samerefrigeration cycle but incorporates both the evaporator and the condenser into the same air path; the air first passes over the evaporator coil, where it is cooled[52] and dehumidified before passing over the condenser coil, where it is warmed again before it is released back into the room.[citation needed]
Free cooling can sometimes be selected when the external air is cooler than the internal air. Therefore, the compressor does not need to be used, resulting in high cooling efficiencies for these times. This may also be combined withseasonal thermal energy storage.[53]
Some air conditioning systems can reverse therefrigeration cycle and act as anair source heat pump, thus heating instead of cooling the indoor environment. They are also commonly referred to as "reverse cycle air conditioners". The heat pump is significantly more energy-efficient thanelectric resistance heating, because it moves energy from air or groundwater to the heated space and the heat from purchased electrical energy. When the heat pump is in heating mode, the indoor evaporator coil switches roles and becomes the condenser coil, producing heat. The outdoor condenser unit also switches roles to serve as the evaporator and discharges cold air (colder than the ambient outdoor air).
Most air source heat pumps become less efficient in outdoor temperatures lower than 4 °C or 40 °F.[54] This is partly because ice forms on the outdoor unit's heat exchanger coil, which blocks air flow over the coil. To compensate for this, the heat pump system must temporarily switch back into the regular air conditioning mode to switch the outdoor evaporator coilback to the condenser coil, to heat up and defrost. Therefore, some heat pump systems will have electric resistance heating in the indoor air path that is activated only in this mode to compensate for the temporary indoor air cooling, which would otherwise be uncomfortable in the winter.
Newer models have improved cold-weather performance, with efficient heating capacity down to −14 °F (−26 °C).[55][54][56] However, there is always a chance that the humidity that condenses on the heat exchanger of the outdoor unit could freeze, even in models that have improved cold-weather performance, requiring a defrosting cycle to be performed.
The icing problem becomes much more severe with lower outdoor temperatures, so heat pumps are sometimes installed in tandem with a more conventional form of heating, such as an electrical heater, anatural gas,heating oil, or wood-burningfireplace orcentral heating, which is used instead of or in addition to the heat pump during harsher winter temperatures. In this case, the heat pump is used efficiently during milder temperatures, and the system is switched to the conventional heat source when the outdoor temperature is lower.
Thecoefficient of performance (COP) of an air conditioning system is a ratio of useful heating or cooling provided to the work required.[57][58] Higher COPs equate to lower operating costs. The COP usually exceeds 1; however, the exact value is highly dependent on operating conditions, especially absolute temperature and relative temperature between sink and system, and is often graphed or averaged against expected conditions.[59] Air conditioner equipment power in the U.S. is often described in terms of "tons of refrigeration", with each approximately equal to the cooling power of oneshort ton (2,000 pounds (910 kg) of ice melting in a 24-hour period. The value is equal to 12,000BTUIT per hour, or 3,517watts.[60] Residential central air systems are usually from 1 to 5 tons (3.5 to 18 kW) in capacity.[citation needed]
Efficiency is strongly affected by the humidity of the air to be cooled.Dehumidifying the air before attempting to cool it can reduce subsequent cooling costs by as much as 90 percent. Thus, reducing dehumidifying costs can materially affect overall air conditioning costs.[62]
This type of controller uses aninfraredLED to relay commands from a remote control to the air conditioner. The output of the infrared LED (like that of any infrared remote) is invisible to the human eye because its wavelength is beyond the range of visible light (940 nm). This system is commonly used on mini-split air conditioners because it is simple and portable. Some window and ducted central air conditioners uses it as well.
A wired controller, also called a "wired thermostat," is a device that controls an air conditioner by switching heating or cooling on or off. It uses differentsensors to measure temperatures and actuate control operations. Mechanical thermostats commonly usebimetallic strips, converting a temperature change into mechanical displacement, to actuate control of the air conditioner. Electronic thermostats, instead, use athermistor or other semiconductor sensor, processing temperature change as electronic signals to control the air conditioner.
These controllers are usually used inhotel rooms because they are permanently installed into a wall and hard-wired directly into the air conditioner unit, eliminating the need for batteries.
Evaporator, indoor unit, or terminal, side of a ductless split-type air conditioner
Ductless systems (often mini-split, though there are now ducted mini-split) typically supply conditioned and heated air to a single or a few rooms of a building, without ducts and in a decentralized manner.[63] Multi-zone or multi-split systems are a common application of ductless systems and allow up to eight rooms (zones or locations) to be conditioned independently from each other, each with its indoor unit and simultaneously from a single outdoor unit.
The first mini-split system was sold in 1961 byToshiba in Japan, and the first wall-mounted mini-split air conditioner was sold in 1968 in Japan byMitsubishi Electric, where small home sizes motivated their development. The Mitsubishi model was the first air conditioner with across-flow fan.[64][65][66] In 1969, the first mini-split air conditioner was sold in the US.[67] Multi-zone ductless systems were invented byDaikin in 1973, andvariable refrigerant flow systems (which can be thought of as larger multi-split systems) were also invented by Daikin in 1982. Both were first sold in Japan.[68] Variable refrigerant flow systems when compared with central plant cooling from anair handler, eliminate the need for large cool air ducts, air handlers, and chillers; instead cool refrigerant is transported through much smaller pipes to the indoor units in the spaces to be conditioned, thus allowing for less space abovedropped ceilings and a lower structural impact, while also allowing for more individual and independent temperature control of spaces. The outdoor and indoor units can be spread across the building.[69] Variable refrigerant flow indoor units can also be turned off individually in unused spaces.[citation needed] The lower start-up power of VRF's DC inverter compressors and their inherent DC power requirements also allow VRFsolar-powered heat pumps to be run using DC-providing solar panels.
Split-system central air conditioners consist of twoheat exchangers, an outside unit (thecondenser) from which heat is rejected to the environment and an internal heat exchanger (theevaporator, or Fan Coil Unit, FCU) with the piped refrigerant being circulated between the two. The FCU is then connected to the spaces to be cooled byventilation ducts.[70] Floor standing air conditioners are similar to this type of air conditioner but sit within spaces that need cooling.
Industrial air conditioners on top of the shopping mallPassage in Linz, Austria
Large central cooling plants may use intermediatecoolant such aschilled water pumped intoair handlers orfan coil units near or in the spaces to be cooled which then duct or deliver cold air into the spaces to be conditioned, rather than ducting cold air directly to these spaces from the plant, which is not done due to the low density andheat capacity of air, which would require impractically large ducts. The chilled water is cooled bychillers in the plant, which uses a refrigeration cycle to cool water, often transferring its heat to the atmosphere even in liquid-cooled chillers through the use ofcooling towers. Chillers may be air- or liquid-cooled.[71][72]
A portable system has an indoor unit on wheels connected to an outdoor unit via flexible pipes, similar to a permanently fixed installed unit (such as a ductless split air conditioner).
Hose systems, which can bemonoblock orair-to-air, are vented to the outside via air ducts. Themonoblock type collects the water in a bucket or tray and stops when full. Theair-to-air type re-evaporates the water, discharges it through the ducted hose, and can run continuously. Many but not all portable units draw indoor air and expel it outdoors through a single duct, negatively impacting their overall cooling efficiency.
Many portable air conditioners come with heat as well as a dehumidification function.[73]
Thepackaged terminal air conditioner (PTAC), through-the-wall, and window air conditioners are similar. These units are installed on a window frame or on a wall opening. The unit usually has an internal partition separating its indoor and outdoor sides, which contain the unit's condenser and evaporator, respectively. PTAC systems may be adapted to provide heating in cold weather, either directly by using an electric strip,gas, or other heaters, or by reversing the refrigerant flow to heat the interior and draw heat from the exterior air, converting the air conditioner into aheat pump. They may be installed in a wall opening with the help of a special sleeve on the wall and a custom grill that is flush with the wall and window air conditioners can also be installed in a window, but without a custom grill.[74]
Packaged air conditioners (also known as self-contained units)[75][76] are central systems that integrate into a single housing all the components of a split central system, and deliver air, possibly through ducts, to the spaces to be cooled. Depending on their construction they may be outdoors or indoors, on roofs (rooftop units),[77][78] draw the air to be conditioned from inside or outside a building and be water or air-cooled. Often, outdoor units are air-cooled while indoor units are liquid-cooled using a cooling tower.[70][79][80][81][82][83]
This compressor uses two interleaving scrolls to compress the refrigerant.[84] it consists of one fixed and one orbiting scrolls. This type of compressor is more efficient because it has 70 percent less moving parts than a reciprocating compressor.[citation needed]
This compressor use two very closely meshing spiral rotors to compress the gas. The gas enters at the suction side and moves through the threads as the screws rotate. The meshing rotors force the gas through the compressor, and the gas exits at the end of the screws. The working area is the inter-lobe volume between the male and female rotors. It is larger at the intake end, and decreases along the length of the rotors until the exhaust port. This change in volume is the compression.[citation needed]
There are several ways to modulate the cooling capacity in refrigeration or air conditioning andheating systems. The most common in air conditioning are: on-off cycling, hot gas bypass, use or not of liquid injection, manifold configurations of multiple compressors,mechanical modulation (also called digital), and inverter technology.[citation needed]
Hot gas bypass involves injecting a quantity of gas from discharge to the suction side. The compressor will keep operating at the same speed, but due to the bypass, therefrigerant mass flow circulating with the system is reduced, and thus the cooling capacity. This naturally causes the compressor to run uselessly during the periods when the bypass is operating. The turn down capacity varies between 0 and 100%.[85]
Several compressors can be installed in the system to provide the peak cooling capacity. Each compressor can run or not in order to stage the cooling capacity of the unit. The turn down capacity is either 0/33/66 or 100% for a trio configuration and either 0/50 or 100% for a tandem.[citation needed]
This internal mechanical capacity modulation is based on periodic compression process with acontrol valve, the two scroll set move apart stopping the compression for a given time period. This method varies refrigerant flow by changing the average time of compression, but not the actual speed of the motor. Despite an excellentturndown ratio – from 10 to 100% of the cooling capacity, mechanically modulated scrolls have highenergy consumption as the motor continuously runs.[citation needed]
This system uses avariable-frequency drive (also called an Inverter) to control the speed of the compressor. The refrigerant flow rate is changed by the change in the speed of the compressor. The turn down ratio depends on the system configuration and manufacturer. It modulates from 15 or 25% up to 100% at full capacity with a single inverter from 12 to 100% with a hybrid tandem. This method is the most efficient way to modulate an air conditioner's capacity. It is up to 58% more efficient than a fixed speed system.[citation needed]
In hot weather, air conditioning can preventheat stroke,dehydration due to excessivesweating,electrolyte imbalance,kidney failure, and other issues due tohyperthermia.[8][86]Heat waves are the most lethal type of weather phenomenon in the United States.[87][88] A 2020 study found that areas with lower use of air conditioning correlated with higher rates of heat-related mortality and hospitalizations.[89] TheAugust 2003 France heatwave resulted in approximately 15,000 deaths, where 80% of the victims were over 75 years old. In response, the French government required all retirement homes to have at least one air-conditioned room at 25 °C (77 °F) per floor during heatwaves.[8]
Air conditioning (including filtration, humidification, cooling and disinfection) can be used to provide a clean, safe,hypoallergenic atmosphere in hospital operating rooms and other environments where proper atmosphere is critical to patient safety and well-being. It is sometimes recommended for home use by people withallergies, especiallymold.[90][91] However, poorly maintained water cooling towers can promote the growth and spread of microorganisms such asLegionella pneumophila, the infectious agent responsible forLegionnaires' disease. As long as the cooling tower is kept clean (usually by means of achlorine treatment), these health hazards can be avoided or reduced. The state of New York has codified requirements for registration, maintenance, and testing of cooling towers to protect againstLegionella.[92]
First designed to benefit targeted industries such as the press as well as large factories, the invention quickly spread to public agencies and administrations with studies with claims of increased productivity close to 24% in places equipped with air conditioning.[93]
Air conditioning caused various shifts in demography, notably that of the United States starting from the 1970s. In the US, thebirth rate was lower in the spring than during other seasons until the 1970s but this difference then declined since then.[94] As of 2007, theSun Belt contained 30% of the total US population while it was inhabited by 24% of Americans at the beginning of the 20th century.[95] Moreover, the summermortality rate in the US, which had been higher in regions subject to a heat wave during the summer, also evened out.[7]
The spread of the use of air conditioning acts as a main driver for the growth of global demand of electricity.[96] According to a 2018 report from theInternational Energy Agency (IEA), it was revealed that the energy consumption for cooling in the United States, involving 328 million Americans, surpasses the combined energy consumption of 4.4 billion people in Africa, Latin America, the Middle East, and Asia (excluding China).[8] A 2020 survey found that an estimated 88% of all US households use AC, increasing to 93% when solely looking at homes built between 2010 and 2020.[97]
Air conditioner farm in the facade of a building in Singapore
Space cooling including air conditioning accounted globally for 2021 terawatt-hours of energy usage in 2016 with around 99% in the form of electricity, according to a 2018 report on air-conditioning efficiency by theInternational Energy Agency.[8] The report predicts an increase of electricity usage due to space cooling to around 6200 TWh by 2050,[8][98] and that with the progress currently seen,greenhouse gas emissions attributable to space cooling will double: 1,135 million tons (2016) to 2,070 million tons.[8] There is some push to increase the energy efficiency of air conditioners.United Nations Environment Programme (UNEP) and the IEA found that if air conditioners could be twice as effective as now, 460 billion tons of GHG could be cut over 40 years.[99] The UNEP and IEA also recommended legislation to decrease the use ofhydrofluorocarbons, better buildinginsulation, and more sustainable temperature-controlled food supply chains going forward.[99]
Refrigerants have also caused and continue to cause serious environmental issues, includingozone depletion andclimate change, as several countries have not yet ratified theKigali Amendment to reduce the consumption and production ofhydrofluorocarbons.[100]CFCs and HCFCsrefrigerants such asR-12 andR-22, respectively, used within air conditioners have caused damage to theozone layer,[101] and hydrofluorocarbon refrigerants such asR-410A andR-404A, which were designed to replace CFCs and HCFCs, are instead exacerbatingclimate change.[102] Both issues happen due to the venting of refrigerant to the atmosphere, such as during repairs.HFO refrigerants, used in some if not most new equipment, solve both issues with an ozone damage potential (ODP) of zero and a much lowerglobal warming potential (GWP) in the single or double digits vs. the three or four digits of hydrofluorocarbons.[103]
Hydrofluorocarbons would have raised global temperatures by around 0.3–0.5 °C (0.5–0.9 °F) by 2100 without theKigali Amendment. With theKigali Amendment, the increase of global temperatures by 2100 due to hydrofluorocarbons is predicted to be around 0.06 °C (0.1 °F).[104]
Alternatives to continual air conditioning includepassive cooling, passive solar cooling, natural ventilation, operating shades to reduce solar gain, using trees, architectural shades, windows (and using window coatings) to reducesolar gain.[citation needed]
Socioeconomic groups with a household income below around $10,000 tend to have a low air conditioning adoption,[42] which worsens heat-related mortality.[7] The lack of cooling can be hazardous, as areas with lower use of air conditioning correlate with higher rates of heat-related mortality and hospitalizations.[89] Premature mortality in NYC is projected to grow between 47% and 95% in 30 years, with lower-income and vulnerable populations most at risk.[89] Studies on the correlation between heat-related mortality and hospitalizations and living in low socioeconomic locations can be traced in Phoenix, Arizona,[105] Hong Kong,[106] China,[106] Japan,[107] and Italy.[108][109] Additionally, costs concerning health care can act as another barrier, as the lack of private health insurance during a 2009 heat wave in Australia, was associated with heat-related hospitalization.[109]
Disparities insocioeconomic status and access to air conditioning are connected by some toinstitutionalized racism, which leads to the association of specific marginalized communities with lower economic status, poorer health, residing in hotter neighborhoods, engaging in physically demanding labor, and experiencing limited access to cooling technologies such as air conditioning.[109] A study overlooking Chicago, Illinois, Detroit, and Michigan found that black households were half as likely to have central air conditioning units when compared to their white counterparts.[110] Especially in cities, Redlining createsheat islands, increasing temperatures in certain parts of the city.[109] This is due to materials heat-absorbing building materials and pavements and lack of vegetation and shade coverage.[111] There have been initiatives that provide cooling solutions to low-income communities, such as publiccooling spaces.[8][111]
Buildings designed with passive air conditioning are generally less expensive to construct and maintain than buildings with conventionalHVAC systems with lower energy demands.[112] While tens of air changes per hour, and cooling of tens of degrees, can be achieved with passive methods, site-specificmicroclimate must be taken into account, complicatingbuilding design.[12]
Many techniques can be used to increase comfort and reduce the temperature in buildings. These include evaporative cooling, selective shading, wind,thermal convection, and heat storage.[113]
The ventilation system of a regularearthshipDogtrot houses are designed to maximise natural ventilation.Aroof turbine ventilator, colloquially known as a 'Whirly Bird' is an application of wind driven ventilation.
Passive ventilation is the process of supplying air to and removing air from an indoor space without usingmechanical systems. It refers to the flow of external air to an indoor space as a result ofpressure differences arising from natural forces.
There are two types of naturalventilation occurring in buildings:wind driven ventilation andbuoyancy-driven ventilation. Wind driven ventilation arises from the different pressures created by wind around a building or structure, and openings being formed on the perimeter which then permit flow through the building. Buoyancy-driven ventilation occurs as a result of the directional buoyancy force that results from temperature differences between the interior and exterior.[114]
Since the internal heat gains which create temperature differences between the interior and exterior are created by natural processes, including the heat from people, and wind effects are variable, naturally ventilated buildings are sometimes called "breathing buildings".
A traditional Iranian solar cooling design using awind tower
Passive cooling is a building design approach that focuses on heat gain control and heat dissipation in a building in order to improve the indoorthermal comfort with low or no energy consumption.[115][116] This approach works either by preventing heat from entering the interior (heat gain prevention) or by removing heat from the building (natural cooling).[117]
Natural cooling utilizes on-site energy, available from the natural environment, combined with the architectural design of building components (e.g.building envelope), rather than mechanical systems to dissipate heat.[118] Therefore, natural cooling depends not only on the architectural design of the building but on how the site's natural resources are used asheat sinks (i.e. everything that absorbs or dissipates heat). Examples of on-site heat sinks are the upper atmosphere (night sky), the outdoor air (wind), and the earth/soil.
Passive cooling is an important tool for design of buildings forclimate change adaptation – reducing dependency on energy-intensive air conditioning in warming environments.[119][120]
A pair of shortwindcatchers (malqaf) used in traditional architecture; wind is forced down on thewindward side and leaves on theleeward side (cross-ventilation). In the absence of wind, the circulation can be driven with evaporative cooling in the inlet (which is also designed to catch dust). In the center, ashuksheika (roof lantern vent), used to shade theqa'a below while allowing hot air rise out of it (stack effect).[11]
PDRC applications on building roofs andenvelopes have demonstrated significant decreases in energy consumption and costs.[123] Insuburbansingle-family residential areas, PDRC application on roofs can potentially lower energy costs by 26% to 46%.[124] PDRCs are predicted to show a market size of ~$27 billion for indoor space cooling by 2025 and have undergone a surge in research and development since the 2010s.[125][126]
Hand fans have existed sinceprehistory. Large human-powered fans built into buildings include thepunkah.
The 2nd-century Chinese inventorDing Huan of theHan dynasty invented arotary fan for air conditioning, with seven wheels 3 m (10 ft) in diameter and manually powered by prisoners.[127]: 99, 151, 233 In 747,Emperor Xuanzong (r. 712–762) of theTang dynasty (618–907) had the Cool Hall (Liang Dian涼殿) built in the imperial palace, which theTang Yulin describes as havingwater-powered fan wheels for air conditioning as well as risingjet streams of water from fountains. During the subsequentSong dynasty (960–1279), written sources mentioned the air conditioning rotary fan as even more widely used.[127]: 134, 151
In areas that arecold at night or in winter, heat storage is used. Heat may be stored in earth or masonry; air is drawn past the masonry to heat or cool it.[13]
In areas that are below freezing at night in winter, snow and ice can be collected and stored inice houses for later use in cooling.[13] This technique is over 3,700 years old in the Middle East.[128] Harvesting outdoor ice during winter and transporting and storing for use in summer was practiced by wealthy Europeans in the early 1600s,[15] and became popular in Europe and the Americas towards the end of the 1600s.[129] This practice was replaced by mechanical compression-cycleicemakers.
In dry, hot climates, theevaporative cooling effect may be used by placing water at the air intake, such that the draft draws air over water and then into the house. For this reason, it is sometimes said that the fountain, in the architecture of hot, arid climates, is like the fireplace in the architecture of cold climates.[11] Evaporative cooling also makes the air more humid, which can be beneficial in a dry desert climate.[130]
Evaporative coolers tend to feel as if they are not working during times of high humidity, when there is not much dry air with which the coolers can work to make the air as cool as possible for dwelling occupants. Unlike other types of air conditioners, evaporative coolers rely on the outside air to be channeled through cooler pads that cool the air before it reaches the inside of a house through its air duct system; this cooled outside air must be allowed to push the warmer air within the house out through an exhaust opening such as an open door or window.[131]
^abcMohamed, Mady A.A. (January 2010). Lehmann, S.; Waer, H.A.; Al-Qawasmi, J. (eds.).Traditional Ways of Dealing with Climate in Egypt. The Seventh International Conference of Sustainable Architecture and Urban Development (SAUD 2010). Amman, Jordan: The Center for the Study of Architecture in Arab Region (CSAAR Press). pp. 247–266.Archived from the original on May 13, 2021. RetrievedMay 12, 2021.
^Porta, Giambattista Della (1584).Magiae naturalis(PDF). London.LCCN09023451.Archived(PDF) from the original on May 13, 2021. RetrievedMay 12, 2021.In our method I shall observe what our ancestors have said; then I shall show by my own experience, whether they be true or false
^Gulledge III, Charles; Knight, Dennis (February 11, 2016)."Heating, Ventilating, Air-Conditioning, And Refrigerating Engineering". National Institute of Building Sciences.Archived from the original on April 20, 2021. RetrievedMay 12, 2021.Though he did not actually invent air-conditioning nor did he take the first documented scientific approach to applying it, Willis Carrier is credited with integrating the scientific method, engineering, and business of this developing technology and creating the industry we know today as air-conditioning.
See also: Cramer, Stuart W. (1906)"Recent development in air conditioning" in:Proceedings of the Tenth Annual Convention of the American Cotton Manufacturers Association Held at Asheville, North Carolina May 16–17, 1906. Charlotte, North Carolina, USA: Queen City Publishing Co. pp. 182-211.
^Lester, Paul (July 20, 2015)."History of Air Conditioning". United States Department of Energy.Archived from the original on June 5, 2020. RetrievedMay 12, 2021.
^Cornish, Cheryl; Cooper, Stephen; Jenkins, Salima.Characteristics of New Housing (Report). United States Census Bureau.Archived from the original on April 11, 2021. RetrievedMay 12, 2021.
^ab"Cold Climate Air Source Heat Pump"(PDF).Minnesota Department of Commerce, Division of Energy Resources.Archived(PDF) from the original on January 2, 2022. RetrievedMarch 29, 2022.
^Evans, Paul (November 11, 2018)."RTU Rooftop Units explained".The Engineering Mindset.Archived from the original on January 15, 2021. RetrievedMay 12, 2021.
^Glaeser, Edward L.; Tobio, Kristina (January 2008). "The Rise of the Sunbelt".Southern Economic Journal.74 (3):609–643.doi:10.1002/j.2325-8012.2008.tb00856.x.
^Santamouris, M.; Asimakoupolos, D. (1996).Passive cooling of buildings (1st ed.). London: James & James (Science Publishers) Ltd.ISBN978-1-873936-47-4.
^Leo Samuel, D.G.; Shiva Nagendra, S.M.; Maiya, M.P. (August 2013). "Passive alternatives to mechanical air conditioning of building: A review".Building and Environment.66:54–64.Bibcode:2013BuEnv..66...54S.doi:10.1016/j.buildenv.2013.04.016.
^Raman, Aaswath P.; Anoma, Marc Abou; Zhu, Linxiao; Rephaeli, Eden; Fan, Shanhui (November 2014). "Passive radiative cooling below ambient air temperature under direct sunlight".Nature.515 (7528):540–544.Bibcode:2014Natur.515..540R.doi:10.1038/nature13883.PMID25428501.
^abBijarniya, Jay Prakash; Sarkar, Jahar; Maiti, Pralay (November 2020). "Review on passive daytime radiative cooling: Fundamentals, recent researches, challenges and opportunities".Renewable and Sustainable Energy Reviews.133: 110263.Bibcode:2020RSERv.13310263B.doi:10.1016/j.rser.2020.110263.S2CID224874019.
^Mokhtari, Reza; Ulpiani, Giulia; Ghasempour, Roghayeh (July 2022). "The Cooling Station: Combining hydronic radiant cooling and daytime radiative cooling for urban shelters".Applied Thermal Engineering.211: 118493.Bibcode:2022AppTE.21118493M.doi:10.1016/j.applthermaleng.2022.118493.
^abNeedham, Joseph; Wang, Ling (1991).Science and Civilisation in China, Volume 4: Physics and Physical Technology, Part 2, Mechanical Engineering. Cambridge University Press.ISBN978-0521058032.OCLC468144152.
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