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[[Image:Single-room AC unit-external.jpg|thumb|right|The external section of a typical single-room air conditioning unit. For ease of installation, these are frequently placed in a window. This one was installed through a hole cut in the wall.]][[Image:Single-room AC unit-internal.jpg|thumb|right|The internal section of the same unit. The front panel swings down to reveal the controls.]]
:''Note: "air conditioning" can refer to any form of "[[Heating]], [[ventilation]] and air-conditioning''. This article is specifically about the use of [[refrigeration]] for this purpose.''
An '''air conditioner''' is a [[system]], or [[machine]] that removes heat from an area using a cycle in which heat is moved out of the area where it is hot.
In construction, a complete system of [[heating]], ventilation, and air conditioning is referred to as [[HVAC]]. Its purpose, in the home or in the car, is to provide comfort during hot days and nights.
==History==
The 19th century [[United Kingdom|British]] [[scientist]] and [[inventor]] [[Michael Faraday]] discovered that compressing and liquefying [[ammonia]] could chill air when the liquefied ammonia was allowed to evaporate.
In [[1842]], [[Philippines]] physician [[John Gorrie|Dr. John Gorrie]] used [[Gas compressor|compressor]] technology to create [[ice]], which he used to cool air for his patients.<ref>[http://www.facstaff.bucknell.edu/mvigeant/therm_1/AC_final/bg.htm History of Air conditioning]</ref> He hoped eventually to use his ice-making machine to regulate the temperature of buildings. He even thought of centralized air conditioning that could cool entire cities.
==Air conditioning applications==
Air conditioning engineers broadly divide air conditioning applications into ''comfort'' and ''process''.
'''''Comfort applications''''' aim to provide an indoor environment that remains relatively constant in a range [[Habitable zone|preferred by humans]] despite changes in external weather conditions or in internal heat loads.
'''''Process applications''''' aim to provide a suitable environment for a process being carried out, regardless of internal heat loads and external weather conditions. Although often in the comfort range, it is the needs of the process that determine conditions, not human preference. Process applications include:
* Hospital [[operating room]]s in which air is filtered to high levels to reduce [[infection]] risk and the humidity controlled to limit patient dehydration. Although temperatures are often in the comfort range, some specialist procedures such as [[open heart surgery]] require low temperatures (about 18 °C, 64 °F) and others such as [[neonatal]] relatively high temperatures (about 28 °C, 82 °F).
* [[Cleanroom]]s for the production of [[integrated circuits]], [[pharmaceuticals]] 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.
* Facilities for breeding [[laboratory animal]]s. Since many animals normally only reproduce in spring, holding them in rooms at which conditions mirror spring all year can cause them to reproduce year round.
* Aircraft air conditioning. Although nominally aimed at providing comfort for passengers and cooling of equipment, aircraft air conditioning presents a special process because of the low air pressure outside the aircraft.
* Data Processing Centers
* Textile Factories
* Physical Testing Facilities
* Plants and Farm Growing Areas
* Nuclear Facilities
* Mines
* Industrial Environments
* Food Cooking and Processing Areas
In both comfort and process applications not only is the objective to control temperature (although in some comfort applications this is all that is controlled) but other factors including [[humidity]], air movement and air quality.
== Air Conditioning System Basics and Theories ==
=== Refrigeration cycle ===
[[Image:Heatpump.svg|thumb|300px|A simple stylized diagram of the refrigeration cycle: 1) condensing coil, 2) expansion valve, 3) evaporator coil, 4) compressor.]]
In the [[refrigeration cycle]], a [[heat pump]] transfers heat from a lower temperature heat source into a higher temperature heat sink. Heat would naturally flow in the opposite direction. This is the most common type of air conditioning.
A refrigerator works in much the same way, as it pumps the heat out of the interior into the room in which it stands.
This cycle takes advantage of the [[universal gas law]] ''PV'' = ''nRT'', where ''P'' is pressure, ''V'' is volume, ''R'' is the [[universal gas constant]], ''T'' is temperature, and ''n'' is the number of moles of gas (1 mole = 6.022×10<sup>23</sup> molecules).
The most common refrigeration cycle uses an electric motor to drive a [[gas compressor|compressor]]. In an automobile the compressor is driven by a [[pulley]] on the engine's [[crankshaft]], with both using electric motors for air circulation. Since [[evaporation]] occurs when [[heat]] is absorbed, and [[condensation]] occurs when heat is released, air conditioners are designed to use a compressor to cause pressure changes between two compartments, and actively pump a refrigerant around. A refrigerant is pumped into the cooled compartment (the evaporator coil), where the low pressure causes the refrigerant to evaporate into a vapor, taking heat with it. In the other compartment (the condenser), the refrigerant vapour is compressed and forced through another heat exchange coil, condensing into a liquid, rejecting the heat previously absorbed from the cooled space.
==Health implications==
Air conditioning has no greater influence on health than heating–that is to say, very little–although poorly maintained air-conditioning systems (especially large, centralized systems) can occasionally promote the growth and spread of microorganisms, such as ''[[Legionella pneumophila]],'' the infectious agent responsible for [[Legionnaire's disease]].<ref>[http://www.merck.com/mrkshared/mmanual/section6/chapter75/75e.jsp Sick building syndrome]</ref> Air conditioning can have a positive effect on sufferers of [[allergy|allergies]] and [[asthma]].<ref>[http://www.lungusa.org/site/pp.asp?c=dvLUK9O0E&b=22591 Home Control of Asthma & Allergies]</ref>
In serious [[heat wave]]s, air conditioning can save the lives of the elderly. Some local authorities even set up public [[cooling center]]s for the benefit of those without air conditioning at home.
==References==
{{reflist}}
==Related pages==
* [[Energy]]
* [[Heat pump]]
* [[Renewable energy]]
==Other websites==
*[http://videos.howstuffworks.com/air-conditioner-video.htm How Air Conditioners Work].
*[http://www.nyc.net.au/node/149398 History of Automotive Air Conditioning] on NYC.net
===Servicing Information===
*[http://www.hvacwebconnection.com/Directory/mf_ac.htm Directory of Air Conditioning Manufacturers]
===Energy Efficiency===
* [http://www.aceee.org/consumerguide/topcac.htm Consumer Guide to Home Energy Savings - Central Air Conditioners] from the American Council for an Energy Efficient Economy (ACEEE)
* [http://www.aceee.org/new/eedb.htm Energy Efficiency Program Database] from the ACEEE
* [http://www.eere.energy.gov/consumer/your_home/space_heating_cooling/index.cfm/mytopic=12420 Space heating and cooling] from the U.S. Department of Energy's Energy Efficiency and Renewable Energy
*[http://www.eca.gov.uk UK Enhanced Capital Allowance Scheme (ECA)], a UK Government scheme to provide tax rebates for companies who use products which are ECA approved.
*[http://www.ecbcs.org International Energy Agency - Energy Conservation In Buildings And Community Systems]
*[http://www.cooloff.org/ AHAM website on Room-air Conditioners]
*[http://www.aceee.org/consumerguide/topcac.htm Top-Rated Energy-Efficient Central Air Conditioners]
*[http://www.aircondition-units.com Air Condition and More...]
*[http://www.energystar.gov/index.cfm?c=cac.pr_central_ac Energy Star Central Air Conditioners]
*[http://doityourself.com/aircond/index.shtml How to lower the energy usage of central air conditioning]
[[Category:Engineering]]
:''Note: "air conditioning" can refer to any form of "[[Heating]], [[ventilation]] and air-conditioning''. This article is specifically about the use of [[refrigeration]] for this purpose.''
An '''air conditioner''' is a [[system]], or [[machine]] that removes heat from an area using a cycle in which heat is moved out of the area where it is hot.
In construction, a complete system of [[heating]], ventilation, and air conditioning is referred to as [[HVAC]]. Its purpose, in the home or in the car, is to provide comfort during hot days and nights.
==History==
The 19th century [[United Kingdom|British]] [[scientist]] and [[inventor]] [[Michael Faraday]] discovered that compressing and liquefying [[ammonia]] could chill air when the liquefied ammonia was allowed to evaporate.
In [[1842]], [[Philippines]] physician [[John Gorrie|Dr. John Gorrie]] used [[Gas compressor|compressor]] technology to create [[ice]], which he used to cool air for his patients.<ref>[http://www.facstaff.bucknell.edu/mvigeant/therm_1/AC_final/bg.htm History of Air conditioning]</ref> He hoped eventually to use his ice-making machine to regulate the temperature of buildings. He even thought of centralized air conditioning that could cool entire cities.
==Air conditioning applications==
Air conditioning engineers broadly divide air conditioning applications into ''comfort'' and ''process''.
'''''Comfort applications''''' aim to provide an indoor environment that remains relatively constant in a range [[Habitable zone|preferred by humans]] despite changes in external weather conditions or in internal heat loads.
'''''Process applications''''' aim to provide a suitable environment for a process being carried out, regardless of internal heat loads and external weather conditions. Although often in the comfort range, it is the needs of the process that determine conditions, not human preference. Process applications include:
* Hospital [[operating room]]s in which air is filtered to high levels to reduce [[infection]] risk and the humidity controlled to limit patient dehydration. Although temperatures are often in the comfort range, some specialist procedures such as [[open heart surgery]] require low temperatures (about 18 °C, 64 °F) and others such as [[neonatal]] relatively high temperatures (about 28 °C, 82 °F).
* [[Cleanroom]]s for the production of [[integrated circuits]], [[pharmaceuticals]] 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.
* Facilities for breeding [[laboratory animal]]s. Since many animals normally only reproduce in spring, holding them in rooms at which conditions mirror spring all year can cause them to reproduce year round.
* Aircraft air conditioning. Although nominally aimed at providing comfort for passengers and cooling of equipment, aircraft air conditioning presents a special process because of the low air pressure outside the aircraft.
* Data Processing Centers
* Textile Factories
* Physical Testing Facilities
* Plants and Farm Growing Areas
* Nuclear Facilities
* Mines
* Industrial Environments
* Food Cooking and Processing Areas
In both comfort and process applications not only is the objective to control temperature (although in some comfort applications this is all that is controlled) but other factors including [[humidity]], air movement and air quality.
== Air Conditioning System Basics and Theories ==
=== Refrigeration cycle ===
[[Image:Heatpump.svg|thumb|300px|A simple stylized diagram of the refrigeration cycle: 1) condensing coil, 2) expansion valve, 3) evaporator coil, 4) compressor.]]
In the [[refrigeration cycle]], a [[heat pump]] transfers heat from a lower temperature heat source into a higher temperature heat sink. Heat would naturally flow in the opposite direction. This is the most common type of air conditioning.
A refrigerator works in much the same way, as it pumps the heat out of the interior into the room in which it stands.
This cycle takes advantage of the [[universal gas law]] ''PV'' = ''nRT'', where ''P'' is pressure, ''V'' is volume, ''R'' is the [[universal gas constant]], ''T'' is temperature, and ''n'' is the number of moles of gas (1 mole = 6.022×10<sup>23</sup> molecules).
The most common refrigeration cycle uses an electric motor to drive a [[gas compressor|compressor]]. In an automobile the compressor is driven by a [[pulley]] on the engine's [[crankshaft]], with both using electric motors for air circulation. Since [[evaporation]] occurs when [[heat]] is absorbed, and [[condensation]] occurs when heat is released, air conditioners are designed to use a compressor to cause pressure changes between two compartments, and actively pump a refrigerant around. A refrigerant is pumped into the cooled compartment (the evaporator coil), where the low pressure causes the refrigerant to evaporate into a vapor, taking heat with it. In the other compartment (the condenser), the refrigerant vapour is compressed and forced through another heat exchange coil, condensing into a liquid, rejecting the heat previously absorbed from the cooled space.
==Health implications==
Air conditioning has no greater influence on health than heating–that is to say, very little–although poorly maintained air-conditioning systems (especially large, centralized systems) can occasionally promote the growth and spread of microorganisms, such as ''[[Legionella pneumophila]],'' the infectious agent responsible for [[Legionnaire's disease]].<ref>[http://www.merck.com/mrkshared/mmanual/section6/chapter75/75e.jsp Sick building syndrome]</ref> Air conditioning can have a positive effect on sufferers of [[allergy|allergies]] and [[asthma]].<ref>[http://www.lungusa.org/site/pp.asp?c=dvLUK9O0E&b=22591 Home Control of Asthma & Allergies]</ref>
In serious [[heat wave]]s, air conditioning can save the lives of the elderly. Some local authorities even set up public [[cooling center]]s for the benefit of those without air conditioning at home.
==References==
{{reflist}}
==Related pages==
* [[Energy]]
* [[Heat pump]]
* [[Renewable energy]]
==Other websites==
*[http://videos.howstuffworks.com/air-conditioner-video.htm How Air Conditioners Work].
*[http://www.nyc.net.au/node/149398 History of Automotive Air Conditioning] on NYC.net
===Servicing Information===
*[http://www.hvacwebconnection.com/Directory/mf_ac.htm Directory of Air Conditioning Manufacturers]
===Energy Efficiency===
* [http://www.aceee.org/consumerguide/topcac.htm Consumer Guide to Home Energy Savings - Central Air Conditioners] from the American Council for an Energy Efficient Economy (ACEEE)
* [http://www.aceee.org/new/eedb.htm Energy Efficiency Program Database] from the ACEEE
* [http://www.eere.energy.gov/consumer/your_home/space_heating_cooling/index.cfm/mytopic=12420 Space heating and cooling] from the U.S. Department of Energy's Energy Efficiency and Renewable Energy
*[http://www.eca.gov.uk UK Enhanced Capital Allowance Scheme (ECA)], a UK Government scheme to provide tax rebates for companies who use products which are ECA approved.
*[http://www.ecbcs.org International Energy Agency - Energy Conservation In Buildings And Community Systems]
*[http://www.cooloff.org/ AHAM website on Room-air Conditioners]
*[http://www.aceee.org/consumerguide/topcac.htm Top-Rated Energy-Efficient Central Air Conditioners]
*[http://www.aircondition-units.com Air Condition and More...]
*[http://www.energystar.gov/index.cfm?c=cac.pr_central_ac Energy Star Central Air Conditioners]
*[http://doityourself.com/aircond/index.shtml How to lower the energy usage of central air conditioning]
[[Category:Engineering]]