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A wall mounted air conditioning unitAir conditioning (often referred to as AC, A/C, or air con) is the process of removing heat and moisture from the interior of an occupied space to improve the comfort of occupants. Air conditioning can be used in both domestic and commercial environments.

This process is most commonly used to achieve a more comfortable interior environment, typically for humans and other animals; however, air conditioning is also used to cool and dehumidify rooms filled with heat-producing electronic devices, such as, and to display and store some delicate products, such as artwork.Air conditioners often use a fan to distribute the conditioned air to an occupied space such as a building or a to improve. Electric refrigerant-based AC units range from small units that can cool a small bedroom, which can be carried by a single adult, to massive units installed on the roof of office towers that can cool an entire building. The is typically achieved through a, but sometimes or is used.

Air conditioning systems can also be made based on (chemicals which remove moisture from the air). Reject or store heat in subterranean pipes.In, a complete system of heating, and air conditioning is referred to as. Contents.History Evaporative cooling Since prehistoric times, snow and ice were used for cooling. The business of harvesting ice during winter and storing for use in summer became popular towards the late 17th century. This practice was replaced by mechanical ice-making machines.The basic concept behind air conditioning is said to have been applied in, where reeds were hung in windows and were moistened with trickling water. The evaporation of water cooled the air blowing through the window. This process also made the air more humid, which can be beneficial in a dry desert climate.

Other techniques in medieval involved the use of and to cool buildings during the hot season.The 2nd-century Chinese mechanical engineer and inventor of the invented a for air conditioning, with seven wheels 3 m (10 ft) in diameter and manually powered by prisoners. 712–762) of the (618–907) had the Cool Hall ( Liang Dian 涼殿) built in the imperial palace, which the Tang Yulin describes as having fan wheels for air conditioning as well as rising jet streams of water from fountains. During the subsequent (960–1279), written sources mentioned the air conditioning rotary fan as even more widely used.In the 17th century, the Dutch inventor demonstrated 'Turning Summer into Winter' as an early form of modern air conditioning for by adding salt to water. Development of mechanical cooling. Three-quarters scale model of Gorrie's ice machine at, FloridaIn 1758, and, a chemistry professor at, conducted an experiment to explore the principle of evaporation as a means to rapidly cool an object. Franklin and Hadley confirmed that evaporation of highly volatile liquids (such as alcohol and ether) could be used to drive down the temperature of an object past the freezing point of water.

They conducted their experiment with the bulb of a mercury thermometer as their object and with a bellows used to speed up the. 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.' In 1820, English scientist and inventor discovered that compressing and liquefying could chill air when the liquefied ammonia was allowed to evaporate.

In 1842, physician used compressor technology to create ice, which he used to cool air for his patients in his hospital in,. He hoped to eventually use his ice-making machine to regulate the temperature of buildings. He even envisioned centralized air conditioning that could cool entire cities.

Though his prototype leaked and performed irregularly, Gorrie was granted a patent in 1851 for his ice-making machine. Though his process improved the artificial production of ice, his hopes for its success vanished soon afterwards when his chief financial backer died and Gorrie did not get the money he needed to develop the machine. According to his biographer, Vivian M. Sherlock, he blamed the 'Ice King', for his failure, suspecting that Tudor had launched a against his invention. Gorrie died impoverished in 1855, and the dream of commonplace air conditioning went away for 50 years.

's first mechanical ice-making machine began operation in 1851 on the banks of the at Rocky Point in, Australia. His first commercial ice-making machine followed in 1853, and his patent for an ether compression refrigeration system was granted in 1855. This novel system used a compressor to force the refrigeration gas to pass through a condenser, where it cooled down and liquefied. The liquefied gas then circulated through the refrigeration coils and vaporized again, cooling down the surrounding system. The machine produced 3,000 kilograms (6,600 lb) of ice per day. Though Harrison had commercial success establishing a second ice company back in Sydney in 1860, he later entered the debate over how to compete against the American advantage of ice-refrigerated beef sales to the. He wrote: 'Fresh meat frozen and packed as if for a voyage, so that the refrigerating process may be continued for any required period', and in 1873 prepared the sailing ship Norfolk for an experimental beef shipment to the United Kingdom.

His choice of a cold room system instead of installing a refrigeration system upon the ship itself proved disastrous when the ice was consumed faster than expected. Electrical air conditioning. The creation of the modern electrical air conditioning unit and industry is credited to the American inventor. After graduating from, Carrier found a job at the. There, he began experimenting with air conditioning as a way to solve an application problem for the Sackett-Wilhelms Lithographing and Publishing Company in. The first air conditioner, designed and built in by Carrier, began working on 17 July 1902.

Designed to improve manufacturing in a plant, Carrier's invention controlled not only but also. Carrier used his knowledge of the heating of objects with steam and reversed the process. Instead of sending air through hot coils, he sent it through cold coils (filled with cold water). The air was cooled, and thereby the amount of moisture in the air could be controlled, which in turn made the humidity in the room controllable.

The controlled temperature and humidity helped maintain consistent paper dimensions and ink alignment. Later, Carrier's technology was applied to increase productivity in the workplace, and was formed to meet rising demand.

Over time, air conditioning came to be used to improve comfort in homes and as well. Residential sales expanded dramatically in the 1950s. In 1906, of was exploring ways to add moisture to the air in his textile mill. Cramer coined the term 'air conditioning', using it in a patent claim he filed that year as an analogue to 'water conditioning', then a well-known process for making textiles easier to process. He combined moisture with ventilation to 'condition' and change the air in the factories, controlling the humidity so necessary in textile plants. Willis Carrier adopted the term and incorporated it into the name of his company.Shortly thereafter, the first private home to have air conditioning was built in Minneapolis in 1914, owned.

Realizing that air conditioning would one day be a standard feature of private homes, particularly in regions with warmer climate, (1898-1994) designed a network of ductwork and vents for his home Meadowmont, all disguised behind intricate and attractive Georgian-style open moldings. This building is believed to be one of the first private homes in the United States equipped for.In 1945, of invented a portable, in-window air conditioner that cooled, heated, humidified, dehumidified, and filtered the air. Refrigerant development. A modern hermetic refrigerationThe first air conditioners and employed toxic or flammable gases, such as, or, that could result in fatal accidents when they leaked. Created the first non-flammable, non-toxic chlorofluorocarbon gas, in 1928. The name is a name owned by for any (CFC), (HCFC), or (HFC) refrigerant.

The refrigerant names include a number indicating the molecular composition (e.g., R-11, R-12, R-22, R-134A). The blend most used in direct-expansion home and building comfort cooling is an HCFC known as (R-22).(R-12) was the most common blend used in automobiles in the U.S. Until 1994, when most designs changed to due to the ozone-depleting potential of R-12. R-11 and R-12 are no longer manufactured in the U.S. For this type of application, but is still imported and can be purchased and used by certified HVAC technicians. For systems requiring only an occasional 'shot' of R-12 and otherwise in good working order and performing far better than virtually all 'R-134a' systems whether 'converted' or 'factory', even $50-$100 per pound of R-12 is considered 'cheap' by many individuals.Modern refrigerants have been developed to be more environmentally safe than many of the early chlorofluorocarbon-based refrigerants used in the early- and mid-twentieth century. These include (, as used in most U.S.

Homes before 2011) and (, used in most cars) have replaced most CFC use. HCFCs, in turn, are supposed to have been in the process of being phased out under the and replaced by HFCs such as, which lack chlorine. HFCs, however, contribute to climate change problems.

Moreover, policy and political influence by corporate executives resisted change. Corporations insisted that no alternatives to HFCs existed.

The environmental organization provided funding to a former East German refrigerator company to research an alternative ozone- and climate-safe refrigerant in 1992. The company developed a hydrocarbon mix of and, but as a condition of the contract with Greenpeace could not patent the technology, which led to its widespread adoption by other firms. Their activist marketing first in Germany led to companies like Whirlpool, Bosch, and later LG and others to incorporate the technology throughout Europe, then Asia, although the corporate executives resisted in Latin America, so that it arrived in Argentina produced by a domestic firm in 2003, and then finally with giant Bosch's production in Brazil by 2004.In 1995, Germany made CFC refrigerators illegal. DuPont and other companies blocked the refrigerant in the U.S. With the U.S. EPA, disparaging the approach as 'that German technology'. Nevertheless, in 2004, Greenpeace worked with multinational corporations like and, and later and others, to create a corporate coalition called Refrigerants Naturally!

Then, four years later, Ben & Jerry's of Unilever and General Electric began to take steps to support production and use in the U.S. In 2011 the EPA decided in favor of the ozone- and climate-safe refrigerant for U.S. Operating principles. An evaporative coolerIn very dry climates, evaporative coolers, sometimes referred to as swamp coolers or desert coolers, are popular for improving coolness during hot weather.

An evaporative cooler is a device that draws outside air through a wet pad, such as a large soaked with water. The of the incoming air, as measured by a, is reduced. The temperature of the incoming air is reduced, but it is also more humid, so the (sensible heat plus latent heat) is unchanged. Some of the sensible heat of the entering air is converted to latent heat by the evaporation of water in the wet cooler pads. If the entering air is dry enough, the results can be quite substantial.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. These coolers cost less and are mechanically simple to understand and maintain.Free cooling.

Main article:Air conditioning can also be provided by a process called which uses pumps to circulate a coolant such as air, water, or a water- mixture from a cold source, which in turn acts as a for the energy that is removed from the cooled space. Common storage media are cool outside air, deep aquifers, or a natural underground rock mass accessed via a cluster of small-diameter boreholes. Some systems with small storage capacity are hybrid systems, using free cooling early in the cooling season, and later employing a heat pump to chill the circulation coming from the storage. The heat pump is added because the temperature of the storage gradually increases during the cooling season, thereby declining its effectiveness.Free cooling systems can have very high efficiencies, and are sometimes combined with (STES) so the cold of winter can be used for summer air conditioning. Free cooling and hybrid systems are. Humidity control Since humans perspire to provide natural cooling by the of from the skin, reducing can promote occupant comfort. An air conditioner designed for an occupied space typically will create a 30% to 60% relative humidity in the occupied space to balance comfort, microbial growth, and other factors.

Dehumidification and cooling 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 the of the surrounding air. Moisture from the air will condense on the coil and must be disposed of or recycled.Dehumidification program Most modern air-conditioning systems feature a dehumidification cycle during which the compressor runs while the fan is slowed as much as possible to reduce the evaporator temperature and therefore condense more water. When the temperature falls below a threshold, both the fan and compressor are shut off to mitigate further temperature drops; this prevents moisture on the evaporator from being blown back into the room. When the temperature rises againthe compressor restarts and the fan returns to low speed.Occasionally, to thaw any ice produced, the fan runs with the compressor shut down; this function is less effective when ambient temperatures are low.

Inverter air conditioners use the inside coil temperature sensor to keep the evaporator as cold as possible. When the evaporator is too coldthe compressor is slowed or stopped with the indoor fan running. Dehumidifier. Typical portable dehumidifierA specialized air conditioner that is used only for dehumidifying is called a. It also uses a, but differs from a standard air conditioner in that both the evaporator and the condenser are placed in the same air path. A standard air conditioner transfers heat energy out of the room because its condenser coil releases heat outside. However, since all components of the dehumidifier are in the same room, no heat energy is removed.

Instead, the electric consumed by the dehumidifier remains in the room as heat, so the room is actually heated, just as by an that draws the same amount of power.In addition, if water is condensed in the room, the amount of heat previously needed to evaporate that water also is re-released in the room (the ). The dehumidification process is the inverse of adding water to the room with an, and instead releases heat. Therefore, an in-room dehumidifier always will warm the room and reduce the relative humidity indirectly, as well as reducing the humidity directly by condensing and removing water.Inside the unit, the air passes over the evaporator coil first, and is cooled and dehumidified. The now dehumidified, cold air then passes over the condenser coil where it is warmed up again. Then the air is released back into the room.

The unit produces warm, dehumidified air and can usually be placed freely in the environment (room) that is to be conditioned.Dehumidifiers are commonly used in cold, damp climates to prevent growth indoors, especially in basements. They are also used to protect sensitive equipment from the adverse effects of excessive humidity in.Energy transfer In a thermodynamically, any power dissipated into the system that is being maintained at a set temperature (which is a standard mode of operation for modern air conditioners) requires that the rate of energy removal by the air conditioner increase. This increase has the effect that, for each unit of energy input into the system (say to power a light bulb in the closed system), the air conditioner removes that energy. To do so, the air conditioner must increase its power consumption by the inverse of its 'efficiency' times the amount of power dissipated into the system.

As an example, assume that inside the closed system a 100 W is activated, and the air conditioner has a coefficient of performance of 200%. The air conditioner's power consumption will increase by 50 W to compensate for this, thus making the 100 W heating element cost a total of 150 W of power.It is typical for air conditioners to operate at 'efficiencies' of significantly greater than 100%. However, it may be noted that the input electrical energy is of higher thermodynamic quality (lower ) than the output thermal energy (heat energy).Air conditioner equipment power in the U.S. Is often described in terms of ', with each approximately equal to the cooling power of one (2000 pounds or 907 kilograms) of ice melting in a 24-hour period. The value is defined as 12,000 per hour, or 3517 watts. Residential central air systems are usually from 1 to 5 tons (3.5 to 18 kW) in capacity.Seasonal energy efficiency ratio.

Main article:For residential homes, some countries set minimum requirements for energy efficiency. In the United States, the efficiency of air conditioners is often (but not always) rated by the seasonal energy efficiency ratio (SEER). The higher the SEER rating, the more energy efficient is the air conditioner. The SEER rating is the BTU of cooling output during its normal annual usage divided by the total electric energy input in (Wh) during the same period.

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Parts of a window unitWindow unit air conditioners are installed in an open window. The interior air is cooled as a fan blows it over the evaporator. On the exterior the heat drawn from the interior is dissipated into the environment as a second fan blows outside air over the condenser.

A large house or building may have several such units, allowing each room to be cooled separately.In 1971, introduced a popular portable in-window air conditioner designed for convenience and portability.systems are also known as wall-split air conditioning systems. They are ductless systems. PTACs, which are frequently used in hotels, have two separate units (terminal packages), the evaporative unit on the interior and the condensing unit on the exterior, with an opening passing through the wall and connecting them.

This minimizes the interior system footprint and allows each room to be adjusted independently. PTAC systems may be adapted to provide heating in cold weather, either directly by using an electric strip, gas, or other heater, or by reversing the refrigerant flow to heat the interior and draw heat from the exterior air, converting the air conditioner into a. While room air conditioning provides maximum flexibility, when used to cool many rooms at a time it is generally more expensive than central air conditioning.The first practical semi-portable air conditioning unit was invented by engineers at and offered for sale starting in 1935. Split systems Split-system air conditioners come in two forms: mini-split and central systems.

In both types, the inside-environment (evaporative) is separated by some distance from the outside-environment (condensing unit) heat exchanger.Mini-split (ductless) system. Evaporator, or terminal, side of a ductless split-type air conditionerA mini-split system typically supplies air conditioned and heated air to a single or a few rooms of a building. Multi-zone systems are a common application of ductless systems and allow up to 8 rooms (zones) to be conditioned from a single outdoor unit.

Multi-zone systems typically offer a variety of indoor unit styles including wall-mounted, ceiling-mounted, ceiling recessed, and horizontal ducted. Mini-split systems typically produce 9,000 to 36,000 Btu (9,500–38,000 kJ) per hour of cooling. Multi-zone systems provide extended cooling and heating capacity up to 60,000 Btu's. Large systems are known as VRF systems. Mini split ductless systems were invented by in 1973, and VRF systems were also invented by Daikin in 1982.Advantages of the ductless system include smaller size and flexibility for zoning or heating and cooling individual rooms. The inside wall space required is significantly reduced. Also, the compressor and heat exchanger can be located farther away from the inside space, rather than merely on the other side of the same unit as in a PTAC or window air conditioner.

Flexible exterior hoses lead from the outside unit to the interior one(s); these are often enclosed with metal to look like common drainpipes from the roof. In addition, ductless systems offer higher efficiency, reaching above 30 SEER.The primary disadvantage of ductless air conditioners is their cost. Such systems cost about US$1,500 to US$2,000 per ton (12,000 BTU per hour) of cooling capacity. This is about 30% more than central systems (not including ductwork) and may cost more than twice as much as window units of similar capacity.'

An additional possible disadvantage is that the cost of installing mini splits can be higher than some systems. However, lower operating costs and or other financial incentives—offered in some areas—can help offset the initial expense. Multi-split system A multi-split system is a conventional split system, which is divided into two parts ( and condenser) and allows cooling or heating of several rooms with one external unit. A central chilled water plant usingCentral cooling plants are used to condition large commercial, industrial, or campus loads. At larger scales, the ductwork required to move conditioned air to and from the plant would be impractically large, so an intermediate fluid such as chilled water is used instead. The plant circulates cold water to terminal chilled water devices such as air handlers or fan/coil units.Portable units A portable air conditioner can be easily transported inside a home or office. They are currently available with capacities of about 5,000–60,000 BTU/h (1,500–18,000 W) and with or without electric-resistance heaters.

Portable air conditioners are either evaporative or refrigerative.The compressor-based refrigerant systems are air-cooled, meaning they use air to exchange heat, in the same way as a car radiator or typical household air conditioner does. Such a system dehumidifies the air as it cools it. It collects water condensed from the cooled air and produces hot air which must be vented outside the cooled area; doing so transfers heat from the air in the cooled area to the outside air.Portable split system A portable system has an indoor unit on wheels connected to an outdoor unit via flexible pipes, similar to a permanently fixed installed unit. The portable units draw indoor air and expel it outdoors through a single duct.

Many portable air conditioners come with heat as well as dehumidification function. Portable hose system Hose systems, which can be monoblock or air-to-air, are vented to the outside via air. The monoblock type collects the water in a bucket or tray and stops when full. The air-to-air type re-evaporates the water and discharges it through the ducted hose and can run continuously.A single-hose unit uses air from within the room to cool its condenser, and then vents it outside. This air is replaced by hot air from outside or other rooms (due to the negative pressure inside the room), thus reducing the unit's overall efficiency.Modern units might have a of approximately 3 (i.e., 1 kW of electricity will produce 3 kW of cooling). A dual-hose unit draws air to cool its condenser from outside instead of from inside the room, and thus is more effective than most single-hose units. These units create no negative pressure in the room.Portable evaporative system , sometimes called 'swamp coolers', do not have a compressor or condenser.

Liquid water is evaporated on the cooling fins, releasing the vapor into the cooled area. Evaporating water absorbs a significant amount of heat, the, cooling the air. Humans and animals use the same mechanism to cool themselves by.Evaporative coolers have the advantage of needing no hoses to vent heat outside the cooled area, making them truly portable. They are also very cheap to install and use less energy than refrigerative air conditioners.Uses Air-conditioning engineers broadly divide air conditioning applications into comfort and process applications.Comfort applications. An array of air conditioners outside a commercial office buildingComfort applications aim to provide a that remains relatively constant despite changes in external weather conditions or in internal heat loads.Air conditioning makes buildings feasible, for otherwise they would have to be built narrower or with so that inner spaces received sufficient outdoor air via.

Air conditioning also allows buildings to be taller, since increases significantly with altitude making natural ventilation impractical for very tall buildings. Typical residential central air conditioners in North AmericaAir conditioning is common in the US, with 88% of new constructed in 2011 including air conditioning, ranging from 99% in the to 62% in the. In, air conditioning use varies by province. In 2013, 55% of Canadian households reported having an air conditioner, with high use in (80%), (78%), (67%), and (54%) and lower use in (23%), (21%), and (9%). In Europe, home air conditioning is generally less common. Countries such as have seen a wide proliferation of home air-conditioning units in recent years. In another southern European country, it is estimated that around 55% of households have an air conditioner installed.

Process applications Process applications aim to provide a suitable environment for a process being carried out, regardless of internal heat and humidity loads and external weather conditions. It is the needs of the process that determine conditions, not human preference. Process applications include these:. and. for the production of, and the like, in which very high levels of air cleanliness and control of temperature and humidity are required for the success of the process.

of. Facilities for breeding. Since many animals normally reproduce only in, holding them in rooms in which conditions mirror those of spring all year can cause them to reproduce year-round. Food and areas. Hospital, in which air is filtered to high levels to reduce risk and the humidity controlled to limit patient dehydration.