Air conditioning is the cooling of indoor air for thermal comfort Human thermal comfort is defined by ASHRAE as the state of mind that expresses satisfaction with the surrounding environment . Maintaining thermal comfort for occupants of buildings or other enclosures is one of the important goals of HVAC design engineers. In a broader sense, the term can refer to any form of cooling, heating, ventilation HVAC is an acronym that stands for the closely related functions of "Heating, Ventilating, and Air Conditioning"—the technology of indoor or automotive environmental comfort. HVAC system design is a major subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics, and heat transfer, or disinfection Disinfectants are substances that are applied to non-living objects to destroy microorganisms that are living on the objects. Disinfection does not necessarily kill all microorganisms, especially not resistant bacterial spores; it is less effective than sterilisation, which is an extreme physical and / or chemical process that kills all types of that modifies the condition of air.^[1] An air conditioner An air conditioner is a home appliance, system, or mechanism designed to dehumidify and extract heat from an area. The cooling is done using a simple refrigeration cycle. In construction, a complete system of heating, ventilation, and air conditioning is referred to as "HVAC". Its purpose, in a building or an automobile, is to provide (often referred to as AC or air con.) is an appliance A major appliance, or domestic appliance, is usually defined as a large machine which accomplishes some routine housekeeping task, which includes purposes such as cooking, food preservation, or cleaning, whether in a household, institutional, commercial or industrial setting. An appliance is differentiated from a plumbing fixture because it uses, system System is a set of interacting or interdependent entities forming an integrated whole, or machine A machine is a device that uses energy to perform some activity. In common usage, the meaning is that of a device having parts that perform or assist in performing any type of work. A simple machine is a device that transforms the direction or magnitude of a force without consuming any energy. The word "machine" is derived from the Latin designed to stabilise the air temperature and humidity within an area (used for cooling as well as heating depending on the air properties at a given time), typically using a refrigeration cycle Thermodynamic heat pump and refrigeration cycles are the models for heat pumps and refrigerators. The difference between a heat pump and a normal air conditioner is that a heat pump can be used to heat a home as well as cool it. Even though the heat pump can heat, it still uses the same basic refrigeration cycle to do this. In other words a heat but sometimes using evaporation Evaporative cooling is especially well suited for climates where the air is hot and humidity is low. For example, in the United States, the western/mountain states are good locations, with swamp coolers very prevalent in cities like Denver, Salt Lake City, Albuquerque, El Paso, Tucson, and Fresno where sufficient water is available. Evaporative, commonly for comfort cooling in buildings and motor vehicles.

The concept of air conditioning is known to have been applied in Ancient Rome Ancient Rome was a civilization that grew out of a small agricultural community founded on the Italian Peninsula as early as the 10th century BC. Located along the Mediterranean Sea, it became one of the largest empires in the ancient world, where aqueduct An aqueduct is a water supply or navigable channel constructed to convey water. In modern engineering, the term is used for any system of pipes, ditches, canals, tunnels, and other structures used for this purpose. In a more restricted use, aqueduct (occasionally water bridge) applies to any bridge or viaduct that transports water—instead of a water was circulated through the walls of certain houses to cool them. Similar techniques in medieval The Middle Ages is a period of European history from the 5th century to the 15th century. The period followed the fall of the Western Roman Empire in 476, and preceded the Early Modern Era. It is the middle period in a three-period division of history: Classical, Medieval, and Modern. The term "Middle Ages" (medium aevum) was coined in Persia Iran (Persian: ایران [ʔiˈɾɒn] ), officially the Islamic Republic of Iran, and formerly known as Persia, is a country in Central Eurasia and Western Asia. The name Iran has been in use natively since the Sassanian era and came into use internationally in 1935, before which the country was widely known as Persia. Both Persia and Iran are involved the use of cisterns A cistern is a waterproof receptacle for holding liquids, usually water. Often cisterns are built to catch and store rainwater. Cisterns are distinguished from wells by their waterproof linings. Modern cisterns range in capacity from a few litres to thousands of cubic metres, effectively forming covered reservoirs and wind towers A windcatcher is a traditional Persian architectural device used for many centuries to create natural ventilation in buildings. It is not known who first invented the windcatcher, but it still can be seen in many countries today. Windcatchers come in various designs: uni-directional, bi-directional, and multi-directional. Examples of windcatchers to cool buildings during the hot season. Modern air conditioning emerged from advances in chemistry Chemistry is the science of matter and the changes it undergoes. The science of matter is also addressed by physics, but while physics takes a more general and fundamental approach, chemistry is more specialized, being concerned with the composition, behavior, structure, and properties of matter, as well as the changes it undergoes during chemical during the 19th century, and the first large-scale electrical air conditioning was invented and used in 1902 by Willis Haviland Carrier Willis Haviland Carrier was an engineer and inventor, and is known as the man who invented modern air conditioning.

History

The 2nd century Chinese China is seen variously as an ancient civilization extending over a large area in East Asia, a nation and/or a multinational entity inventor Ding Huan (fl. Floruit is a Latin verb meaning 'flourished', which denotes the period of time during which a person, school, movement or even species was active. In English, the word is occasionally used as a noun indicating the timeframe in which someone 'flourished' 180) of the Han Dynasty The Han Dynasty was the second imperial dynasty of China, preceded by the Qin Dynasty (221–206 BCE) and succeeded by the Three Kingdoms (220–265 CE). It was founded by the peasant rebel leader Liu Bang, known posthumously as Emperor Gaozu of Han. It was briefly interrupted by the Xin Dynasty (9–23 CE) of the former regent Wang Mang. This invented a rotary fan A fan consists of a rotating arrangement of vanes or blades which act on the air. Usually it is contained within some form of housing or case. This may direct the airflow or increase safety by preventing objects from contacting the fan blades. Most fans are powered by electric motors, but other sources of power may be used, including hydraulic for air conditioning, with seven wheels 3 m (9.8 ft) in diameter and manually powered.^[2] In 747, Emperor Xuanzong Li Longji was born at the Tang Dynasty eastern capital Luoyang in 685, during the first reign of his father Emperor Ruizong – but at that time, Emperor Ruizong's mother Empress Dowager Wu (later known as Wu Zetian), not Emperor Ruizong, was in actual control of power as empress dowager and regent. Li Longji was the third son of Emperor Ruizong, (r. 712–762) of the Tang Dynasty The Tang Dynasty (June 18, 618–June 4, 907) was an imperial dynasty of China preceded by the Sui Dynasty and followed by the Five Dynasties and Ten Kingdoms Period. It was founded by the Li (李) family, who seized power during the decline and collapse of the Sui Empire. The dynasty was interrupted briefly by the Second Zhou Dynasty (October 16, (618–907) had the Cool Hall (Liang Tian) built in the imperial palace, which the Tang Yulin describes as having water-powered Hydraulics is a topic in applied science and engineering dealing with the mechanical properties of liquids. Fluid mechanics provides the theoretical foundation for hydraulics, which focuses on the engineering uses of fluid properties. In fluid power, hydraulics is used for the generation, control, and transmission of power by the use of fan wheels for air conditioning as well as rising jet streams of water from fountains.^[3] During the subsequent Song Dynasty The Song Dynasty was a ruling dynasty in China between 960 and 1279; it succeeded the Five Dynasties and Ten Kingdoms Period, and was followed by the Yuan Dynasty. It was the first government in world history to issue banknotes or paper money, and the first Chinese government to establish a permanent standing navy. This dynasty also saw the first (960–1279), written sources mentioned the air conditioning rotary fan as even more widely used.^[4]

Medieval Persia Greater Iran refers to the regions that have significant Iranian cultural influence. It roughly corresponds to the territory on the Iranian plateau, stretching from the Caucasus to the Indus River in Pakistan and conform to the historical understanding of the full territory of "Iran." It is also widely referred to as Greater Persia in had buildings that used cisterns A cistern is a waterproof receptacle for holding liquids, usually water. Often cisterns are built to catch and store rainwater. Cisterns are distinguished from wells by their waterproof linings. Modern cisterns range in capacity from a few litres to thousands of cubic metres, effectively forming covered reservoirs and wind towers A windcatcher is a traditional Persian architectural device used for many centuries to create natural ventilation in buildings. It is not known who first invented the windcatcher, but it still can be seen in many countries today. Windcatchers come in various designs: uni-directional, bi-directional, and multi-directional. Examples of windcatchers to cool buildings during the hot season: cisterns (large open pools in central courtyards, not underground tanks) collected rain water; wind towers had windows that could catch wind and internal vanes to direct the airflow down into the building, usually over the cistern and out through a downwind cooling tower.^[5] Cistern water evaporated, cooling the air in the building. Wind catchers were widely used throughout the medieval Muslim world The term Muslim world has several meanings. In a cultural sense, it refers to the worldwide community of Muslims, adherents of Islam. This community numbers about 1.3-1.5 billion people, roughly one-fifth of the world population. This community is spread across many different nations and ethnic groups connected by religion and a shared sense of, where they were used for air conditioning in many cities.^[6]

Ventilators Ventilating is the process of "changing" or replacing air in any space to provide high Indoor air quality. i.e. to control temperature or remove moisture, odors, smoke, heat, dust, airborne bacteria, carbon dioxide, and to replenish oxygen. Ventilation is used to remove unpleasant smells and excessive moisture, introduce outside air, to were invented in medieval Egypt During the initial Islamic invasion in 639 AD, Egypt was ruled at first by governors acting in the name of the Righteous Caliphs, and then the Ummayad Caliphs in Damascus but, in 747, the Ummayads were overthrown and the power of the Arabs slowly began to weaken. Although Egypt remained under the nominal rule of the Abbasid Caliphate, its rulers and were widely used in many houses throughout Cairo Cairo is the capital of Egypt, and the largest city in Africa, and the Arab World, as well as one of the most densely populated cities in the world. Nicknamed "The City of a Thousand Minarets" for its preponderance of Islamic architecture, Cairo has long been a center of the region's political and cultural life. Even before Cairo was during the Middle Ages The Middle Ages is a period of European history from the 5th century to the 15th century. The period followed the fall of the Western Roman Empire in 476, and preceded the Early Modern Era. It is the middle period in a three-period division of history: Classical, Medieval, and Modern. The term "Middle Ages" (medium aevum) was coined in. These ventilators were later described in detail by Abd al-Latif al-Baghdadi Abd-al-latif, Abd-el-latif or Abd-ul-Latif , also known as al-Baghdadi (Arabic,عبداللطيف البغدادي), born in Baghdad, Iraq, was a celebrated physician, historian, Egyptologist and traveller, and one of the most voluminous writers of the Near East in his time in 1200, who reported that almost every house in Cairo had a ventilator, and that they cost anywhere from 1 to 500 dinars The Dinar is the name of the official currency in several countries. The Gold Dinar was a coin dating back to the early days of Islam, issued by many rulers, and the Islamic gold dinar is a modern revival of it as a coin or unit of account, separate from the currencies listed below. The name of the Gold Dinar was derived from denarius, a Roman depending on their sizes and shapes. Most ventilators in the city were oriented towards the Qibla Qiblah is an Arabic word for the direction that should be faced when a Muslim prays during Salah. Most mosques contain a niche in a wall that indicates the Qiblah, as was the city in general.^[7]

In the 1600s Cornelius Drebbel Cornelis Jacobszoon Drebbel was the Dutch inventor of the first navigable submarine in 1620. Drebbel was an innovator who contributed to the development of measurement and control systems, optics and chemistry demonstrated "turning Summer into Winter" for James I of England James VI & I was King of Scots as James VI from 1567 to 1625, and King of England and Ireland as James I from 1603 to 1625 by adding salt to water.^[8]

In 1758, Benjamin Franklin Benjamin Franklin was one of the Founding Fathers of the United States. A noted polymath, Franklin was a leading author and printer, satirist, political theorist, politician, postmaster, scientist, inventor, civic activist, statesman, and diplomat. As a scientist, he was a major figure in the American Enlightenment and the history of physics for and John Hadley, a chemistry professor at Cambridge University The University of Cambridge is the second oldest university in England and the fourth oldest in the world. In post-nominals the university's name is abbreviated as Cantab, a shortened form of Cantabrigiensis (an adjective derived from Cantabrigia, the Latinised form of Cambridge), 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 "quicken" the evaporation; they lowered the temperature of the thermometer bulb down to 7°F while the ambient temperature was 65°F. Franklin noted that soon after they passed the freezing point of water (32°F) a thin film of ice formed on the surface of the thermometer's bulb and that the ice mass was about a quarter inch thick when they stopped the experiment upon reaching 7°F. Franklin concluded, "From this experiment, one may see the possibility of freezing a man to death on a warm summer's day".^[9]

In 1820, British The United Kingdom of Great Britain and Ireland was the formal name of the United Kingdom from 1 January 1801 until 12 April 1927. It was formed by the merger of the Kingdom of Great Britain and the Kingdom of Ireland, with Ireland being governed directly from Westminster through its Dublin Castle administration scientist and inventor An invention is a new composition, device, or process. An invention may be derived from a pre-existing model or idea, or it could be independently conceived in which case it may be a radical breakthrough. In addition, there is cultural invention, which is an innovative set of useful social behaviors adopted by people and passed on to others Michael Faraday Michael Faraday, FRS was an English chemist and physicist (or natural philosopher, in the terminology of the time) who contributed to the fields of electromagnetism and electrochemistry discovered that compressing and liquefying ammonia Ammonia is a compound of nitrogen and hydrogen with the formula NH3. It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or indirectly, is also a building block for the synthesis of could chill air when the liquefied ammonia was allowed to evaporate. In 1842, Florida With an area of 65,758 square miles , it is ranked 22nd in size among the 50 U.S. states. Florida has the most coastline in the Contiguous United States encompassing approximately 1,200 miles. The state has four large urban areas, a number of smaller industrial cities, and many small towns physician John Gorrie John Gorrie , physician, scientist, inventor, and humanitarian, is considered the father of refrigeration and air conditioning. He was born on the Island of Nevis to Scottish parents on October 3, 1802, and spent his childhood in South Carolina. He received his medical education at the College of Physicians and Surgeons of the Western District of used compressor technology to create ice, which he used to cool air for his patients in his hospital in Apalachicola, Florida Apalachicola is a city in Franklin County, Florida on US 98 about 80 miles southwest of Tallahassee. The population was 2,334 at the 2000 census. The 2005 census estimates gave the city at 2,340. Apalachicola is the county seat of Franklin County.^[10] He hoped eventually to use his ice-making machine to regulate the temperature of buildings. He even envisioned centralized air conditioning that could cool entire cities.^[11] Though his prototype leaked and performed irregularly, Gorrie was granted a patent in 1851 for his ice-making machine. His hopes for its success vanished soon afterwards when his chief financial backer died; Gorrie did not get the money he needed to develop the machine. According to his biographer, Vivian M. Sherlock, he blamed the "Ice King", Frederic Tudor Frederic Tudor was known as Boston's "Ice King", and was the founder of the Tudor Ice Company. During the early 19th Century, he made a fortune shipping ice to the Caribbean, Europe, and even as far away as India from sources of fresh water ice in New England, for his failure, suspecting that Tudor had launched a smear campaign A smear campaign, smear tactic or simply smear is a metaphor for activity that can harm an individual or group's reputation by conflation with a stigmatized group. Sometimes smear is used more generally to include any reputation-damaging activity, including such colloquialisms as mud slinging against his invention. Dr. Gorrie died impoverished in 1855 and the idea of air conditioning faded away for 50 years.

In 1902, the first modern electrical air conditioning unit was invented An invention is a new composition, device, or process. An invention may be derived from a pre-existing model or idea, or it could be independently conceived in which case it may be a radical breakthrough. In addition, there is cultural invention, which is an innovative set of useful social behaviors adopted by people and passed on to others by Willis Haviland Carrier in Buffalo, New York. After graduating from Cornell University, Carrier, a native of Angola, New York, found a job at the Buffalo Forge Company. While there, Carrier began experimentation with air conditioning as a way to solve an application problem for the Sackett-Wilhelms Lithographing and Publishing Company in Brooklyn, New York, and the first "air conditioner," designed and built in Buffalo by Carrier, began working on 17 July 1902.

Designed to improve manufacturing process control in a printing plant, Carrier's invention controlled not only temperature but also humidity. 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 (ones filled with cold water). The air blowing over the cold coils cooled the air, and one could thereby control the amount of moisture the colder air could hold. In turn, the humidity in the room could be controlled. The low heat and humidity were to help maintain consistent paper dimensions and ink alignment. Later, Carrier's technology was applied to increase productivity in the workplace, and The Carrier Air Conditioning Company of America was formed to meet rising demand. Over time, air conditioning came to be used to improve comfort in homes and automobiles as well. Residential sales expanded dramatically in the 1950s.

In 1906, Stuart W. Cramer of Charlotte, North Carolina 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. This evaporation of water in air, to provide a cooling effect, is now known as evaporative cooling.

The first air conditioners and refrigerators employed toxic or flammable gases like ammonia, methyl chloride, and propane which could result in fatal accidents when they leaked. Thomas Midgley, Jr. created the first chlorofluorocarbon gas, Freon, in 1928.

Freon is a trademark name owned by DuPont for any Chlorofluorocarbon (CFC), Hydrogenated CFC (HCFC), or Hydrofluorocarbon (HFC) refrigerant, the name of each including a number indicating molecular composition (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. It is to be phased out for use in new equipment by 2010 and completely discontinued by 2020. R-12 was the most common blend used in automobiles in the US until 1994 when most changed to R-134A. R-11 and R-12 are no longer manufactured in the US for this type of application, the only source for air conditioning purchase being the cleaned and purified gas recovered from other air conditioner systems. Several non-ozone depleting refrigerants have been developed as alternatives, including R-410A, invented by Honeywell (formerly AlliedSignal) in Buffalo, and sold under the Genetron (R) AZ-20 name. It was first commercially used by Carrier under the brand name Puron.

Innovation in air conditioning technologies continues, with much recent emphasis placed on energy efficiency, and on improving indoor air quality. Reducing climate change impact is an important area of innovation, because in addition to greenhouse gas emissions associated with energy use, CFCs, HCFCs and HFCs are, themselves, potent greenhouse gases when leaked to the atmosphere. For example, R-22 (also known as HCFC-22) has a global warming potential about 1,800 times higher than CO₂^[12]. As an alternative to conventional refrigerants, natural alternatives like CO₂ (R-744) have been proposed.^[13]

Air conditioning applications

Air conditioning engineers broadly divide air conditioning applications into comfort and process.

Comfort applications aim to provide a building indoor environment that remains relatively constant in a range preferred by humans despite changes in external weather conditions or in internal heat loads.

Air conditioning makes deep plan buildings feasible, for otherwise they'd have to be built narrower or with light wells so that inner spaces receive sufficient outdoor air via natural ventilation. Air conditioning also allows buildings to be taller since wind speed increases significantly with altitude making natural ventilation impractical for very tall buildings. Comfort applications for various building types are quite different and may be categorized as

• Low-Rise Residential buildings, including single family houses, duplexes, and small apartment buildings
• High-Rise Residential buildings, such as tall dormitories and apartment blocks
• Commercial buildings, which are built for commerce, including offices, malls, shopping centers, restaurants, etc.
• Institutional buildings, which includes hospitals, governmental, academic, and so on.
• Industrial spaces where thermal comfort of workers is desired.

In addition to buildings, air conditioning can be used for many types of transportation — motor-cars and other land vehicles, trains, ships, aircraft, and spacecraft.

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. Although often in the comfort range, it is the needs of the process that determine conditions, not human preference. Process applications include these:

• Hospital operating theatres, 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).
• Cleanrooms 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 animals. 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 challenge because of the changing density associated with changes in altitude, humidity and temperature of the outside air^[vague].
• Data centers
• Textile factories
• Physical testing facilities
• Plants and farm growing areas
• Nuclear facilities
• Chemical and biological laboratories
• Mines
• Industrial environments
• Food cooking and processing areas

In both comfort and process applications, the objective may be to not only control temperature, but also humidity, air quality and air movement from space to space.

Humidity control

Refrigeration air conditioning equipment usually reduces the humidity of the air processed by the system. The relatively cold (below the dewpoint) evaporator coil condenses water vapor from the processed air, (much like an ice-cold drink will condense water on the outside of a glass), sending the water to a drain and removing water vapor from the cooled space and lowering the relative humidity. Since humans perspire to provide natural cooling by the evaporation of perspiration from the skin, drier air (up to a point) improves the comfort provided. The comfort air conditioner is designed to create a 40% to 60% relative humidity in the occupied space. In food retailing establishments, large open chiller cabinets act as highly effective air dehumidifying units.

A specific type of air conditioner that is used only for dehumidifying is called a dehumidifier. A dehumidifier is different from a regular air conditioner in that both the evaporator and condensor coils are placed in the same air path, and the entire unit is placed in the environment that is intended to be conditioned (in this case dehumidified), rather than requiring the condensor coil to be outdoors. Having the condensor coil in the same air path as the evaporator coil produces warm, dehumidified air. The evaporator (cold) coil is placed first in the air path, dehumidifying the air exactly as a regular air conditioner does. The air next passes over the condensor coil re-warming the now dehumidified air. Note that the terms "condensor coil" and "evaporator coil" do not refer to the behavior of water in the air as it passes over each coil; instead they refer to the phases of the refrigeration cycle. Having the condensor coil in the main air path rather than in a separate, outdoor air path (as in a regular air conditioner) results in two consequences—the output air is warm rather than cold, and the unit is able to be placed anywhere in the environment to be conditioned, without a need to have the condensor outdoors.

Unlike a regular air conditioner, a dehumidifier will actually heat a room just as an electric heater that draws the same amount of power (watts) as the dehumidifier. A regular air conditioner transfers energy out of the room by means of the condensor coil, which is outside the room (outdoors). This is a thermodynamic system where the room serves as the system and energy is transferred out of the system. Conversely with a dehumidifier, no energy is transferred out of the thermodynamic system (room) because the air conditioning unit (dehumidifier) is entirely inside the room. Therefore all of the power consumed by the dehumidifier is energy that is input into the thermodynamic system (the room), and remains in the room (as heat). In addition, if the condensed water has been removed from the room, the amount of heat needed to boil that water has been added to the room. This is the inverse of adding water to the room with an evaporative cooler.

Dehumidifiers are commonly used in cold, damp climates to prevent mold growth indoors, especially in basements. They are also sometimes used in hot, humid climates for comfort because they reduce the humidity which causes discomfort (just as a regular air conditioner, but without cooling the room).

The engineering of physical and thermodynamic properties of gas-vapor mixtures is named Psychrometrics.

Health implications

A poorly maintained air-conditioning system can occasionally promote the growth and spread of microorganisms, such as Legionella pneumophila, the infectious agent responsible for Legionnaires' disease, or thermophilic actinomycetes,^[14] but as long as the air conditioner is kept clean these health hazards can be avoided. Conversely, air conditioning, including filtration, humidification, cooling, disinfection, etc., can be used to provide a clean, safe, hypoallergenic atmosphere in hospital operating rooms and other environments where an appropriate atmosphere is critical to patient safety and well-being. Air conditioning can have a positive effect on sufferers of allergies and asthma.^[15]

In serious heat waves, air conditioning can save the lives of the elderly. Some local authorities have even set up public cooling centers for people without home air conditioning.

Energy use

In a thermodynamically closed system, any energy input 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 energy removal rate from the air conditioner increases. 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) this requires the air conditioner to remove that energy.^[16] In order to do that the air conditioner must increase its consumption by the inverse of its efficiency times the input of energy. As an example, presume that inside the closed system a 100 watt light bulb is activated, and the air conditioner has an efficiency of 200%. The air conditioner's energy consumption will increase by 50 W to compensate for this, thus making the 100 W light bulb use a total of 150 W of energy.

It is typical for air conditioners to operate at "efficiencies" of significantly greater than 100%.^[17].However it may be noted that the input (electrical) energy is of higher thermodynamic quality than the output which is basically thermal energy (heat dissipated), See Coefficient of performance.

Automobile air conditioners

Air conditioning systems are designed to allow the driver and or passengers to feel more comfortable during uncomfortably warm humid or hot trips in a vehicle. Cars in hot climates often are fitted with air conditioning. There has been much debate and discussion on what the usage of an air conditioner does to the fuel efficiency of a vehicle. Factors such as wind resistance, aerodynamics and engine power and weight have to be factored into finding the true variance between using the air conditioning system and not using it when figuring out difference in actual gas mileage. Other factors on the impact on the engine and an overall engine heat increase can have an impact on the cooling system of the vehicle.

The Packard Motor Car Company was the first automobile manufacturer to build air conditioners into its cars, beginning in 1939.^[18] These air conditioners were originally optional, and could be installed for an extra $274 (about $4,050 in 2007 dollars^[update]).^[19] The system took up half of the entire trunk space, was not very efficient, and had no thermostat or independent shut-off mechanism.^[20] The option was discontinued after 1941.^[21]

In 1954, the Nash Ambassador was the first American automobile to boast front-end, fully-integrated heating, ventilating, and air-conditioning system.^[22] The Nash-Kelvinator corporation used its experience in refrigeration to introduce the automobile industry's first compact and affordable, single-unit heating and air conditioning system optional for its 1954 Nash models.^[23][24] This was the first system for the mass market with controls on the dash and an electric clutch.^[25] Marketed under the name of "All-Weather Eye", the Nash system was "a good and remarkably inexpensive" system.^[26] Entirely incorporated within the engine bay, the combined heating and cooling system had cold air for passengers enter through dash-mounted vents.^[24] Nash's exclusive "remarkable advance" was not only the "sophisticated" unified system, but also its $345 price that beat all other systems.^[27]

Most competing systems used a separate heating system and an engine-mounted compressor, driven off of the crankshaft of the engine via a belt, with an evaporator in the car's trunk to deliver cold air through the rear parcel shelf and overhead vents. General Motors made a front mounted air conditioning system optional in 1954 on Pontiacs with a straight eight engine that added separate controls and air distribution. The alternative layout pioneered by Nash "became established practice and continues to form the basis of the modern and more sophisticated automatic climate control systems."^[28]

The innovation was adopted quickly, and by 1960 about 20% of all cars in the U.S. had air-conditioning, with the percentage increasing to 80% in the desert areas of the Southwest.^[29] American Motors made air conditioning standard equipment on all AMC Ambassadors starting with the 1968 model year, a first^[30] in the mass market with a base price starting at $2,671.^[31] By 1969, 54% of the domestic automobiles were equipped with air conditioning, with the system needed not only for passenger comfort, but also to increase the car's resale value.^[19]

Portable air conditioners

A portable air conditioner is one on wheels that can be easily transported inside a home or office. They are currently available with capacities of about 6,000-60,000 BTU/h (1,800-18,000 W output) and with and without electric resistance heaters. Portable air conditioners are either evaporative or refrigerative.

Portable refrigerative air conditioners come in two forms, split and hose. These compressor-based refrigerant systems are air-cooled, meaning they use air to exchange heat, in the same way as a car or typical household air conditioner. 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.

A portable split system has an indoor unit on wheels connected to an outdoor unit via flexible pipes, similar to a permanently fixed installed unit.

Hose systems, which can be air-to-air or monoblock, are vented to the outside via air ducts. 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-duct unit draws air out of the room to cool its condenser, and then vents it outside. This air is replaced by hot air from outside or other rooms, thus reducing efficiency. Modern units might have a COP (Coefficient Of Performance, sometimes called "efficiency") of approximately 3 i.e., 1 kW of electricity will produce 3 kW of cooling. A dual-duct unit draws air from outside to cool its condenser instead of from inside the room, and thus is more efficient than most single-duct units.

Evaporative air coolers, sometimes called "swamp air conditioners", do not have a compressor or condenser. Liquid water is evaporated on the cooling fins, releasing the vapour into the cooled area. Evaporating water absorbs a significant amount of heat, the latent heat of vaporisation, cooling the air — humans and other animals use the same mechanism to cool themselves by sweating. Disadvantages are that unless ambient humidity is low (as in a dry climate) cooling is limited and the cooled air is very humid and can feel clammy. They have the advantage of needing no hoses to vent heat outside the cooled area, making them truly portable; and they are very cheap to install and use less energy than refrigerative air conditioners.

Heat pumps

Heat pump is a term for a type of air conditioner in which the refrigeration cycle is able to be reversed, producing heat instead of cold in the indoor environment. They are also commonly referred to, and marketed as, a reverse cycle air conditioner. Using an air conditioner in this way to produce heat is significantly more efficient than electric resistance heating. Some home-owners elect to have a heat pump system installed, which is actually simply a central air conditioner with heat pump functionality (the refrigeration cycle is reversed in the winter). When the heat pump is enabled, the indoor evaporator coil switches roles and becomes the condenser coil, producing heat. The outdoor condensor unit also switches roles to serve as the evaporator, and produces cold air (colder than the ambient outdoor air).

Heat pumps are more popular in milder winter climates where the temperature is frequently in the range of 40-55°F (4-13°C), because heat pumps become inefficient in more extreme cold. This is due to the problem of the outdoor unit's coil forming ice, 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 coil back to being the condensor coil so that it can heat up and de-ice. A heat pump system therefore will have a form of electric resistance heating in the indoor air path that is activated only in this mode in order to compensate for the temporary air conditioning, which would otherwise generate undesirable cold air in the winter. The icing problem becomes much more prevalent with lower outdoor temperatures, so heat pumps are commonly installed in tandem with a more conventional form of heating, such as a natural gas or oil furnace, which is used instead of the heat pump during harsher winter temperatures. In this case, the heat pump is used efficiently during the milder temperatures, and the system is switched to the conventional heat source when the outdoor temperature is lower.

Absorption heat pumps are actually a kind of air-source heat pumps, but they do not depend on electricity to power them. Instead, gas, solar power, or heated water is used as a main power source. Additionally, refrigerant isn’t used at all in the process. To extract heat, an absorption pump absorbs ammonia into water. Next, the water and ammonia mixture is pressurized to induce boiling, and the ammonia is boiled off. ^[32]

Some more expensive window air conditioning units have the heat pump function. However, a window unit that has a "heat" selection is not necessarily a heat pump because some units use electric resistance heat when heating is desired. A unit that has true heat pump functionality will be indicated in its literature by the term "heat pump".

Professional bodies

American Society of Heating, Refrigerating, and Air-Conditioning Engineers

ASHRAE (American Society of Heating, Refrigerating, and Air-Conditioning Engineers) is an organization devoted to the advancement of indoor-environment-control technology in the heating, ventilation, and air conditioning (HVAC) industry. ASHRAE was founded in 1894 to serve as a source of technical standards and guidelines. Since that time, it has grown into an international society that offers educational information, courses, seminars, career guidance, and publications. The organization also promotes a code of ethics for HVAC professionals and provides for liaison with the general public. Its headquarters are in Atlanta, GA.

Australian Institute of Refrigeration Air Conditioning and Heating

The Australian Institute of Refrigeration Air Conditioning and Heating (AIRAH) was founded in 1920 and currently has around 10,000 members. AIRAH is the official Australian secretariat of the International Institute of Refrigeration (IIR) and collaborates closely with the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE).

Air Conditioning and Mechanical Contractors Association of Australia

The Air Conditioning and Mechanical Contractors Association of Australia (AMCA) is a nation wide industry association dedicated to represent and service the air conditioning and mechanical services industry in Australia. Members of AMCA design, install and provide ongoing service of air conditioning and mechanical ventilation systems.

Air Conditioning Contractors of America (ACCA)

The ACCA is a large organization of American HVACR professionals. They have over four thousand members and have individual charters in each state.^[33]

Refrigeration Service Engineers Society (RSES)

The Refrigeration Service Engineers Society is a public non profit educational organization devoted to furthering the education and career growth of those who install, troubleshoot and repair air conditioning, ventilation, heating and refrigeration equipment. RSES maintains local chapters in most large cities and most states.

See also

• Ground-coupled heat exchanger
• HVAC
• Seawater air conditioning

Notes

1. ^ ASHRAE Terminology of HVAC&R, ASHRAE, Inc., Atlanta, 1991,
2. ^ Needham, Joseph (1986). Science and Civilization: Volume 4, Physics and Physical Technology, Part 2, Mechanical Engineering. Taipei: Caves Books Ltd. Pages 99, 151, 233.
3. ^ Needham, Joseph (1986). Science and Civilization: Volume 4, Physics and Physical Technology, Part 2, Mechanical Engineering. Taipei: Caves Books Ltd. Pages 134 & 151.
4. ^ Needham, Joseph (1986). Science and Civilization: Volume 4, Physics and Physical Technology, Part 2, Mechanical Engineering. Taipei: Caves Books Ltd. Page 151.
5. ^ Ancient air conditioning, The World, January 11, 2007
6. ^ Lindsay, James E. (2005). Daily Life in the Medieval Islamic World. Greenwood Publishing Group. p. 127. ISBN 0313322708
7. ^ David A. King (1984). "Architecture and Astronomy: The Ventilators of Medieval Cairo and Their Secrets", Journal of the American Oriental Society 104 (1), p. 97-133.
8. ^ Laszlo, Pierre (2001-06). Salt: Grain of Life. ISBN 9780231121989. http://books.google.com/?id=DhhN_FthpYMC&pg=PA117&dq=Cornelius+Drebbel+%22air+conditioning%22.
9. ^ Cooling by Evaporation (Letter to John Lining). Benjamin Franklin, London, June 17, 1758
10. ^ History of Air Conditioning Source: Jones Jr., Malcolm. "Air Conditioning". Newsweek. Winter 1997 v130 n24-A p42(2). Retrieved 1 January 2007.
11. ^ The History of Air Conditioning Lou Kren, Properties Magazine Inc. Retrieved 1 January 2007.
12. ^ IPCC Fourth Assessment Report, Table 2.14
13. ^ The current status in Air Conditioning - papers & presentations
14. ^ Sick building syndrome
15. ^ Home Control of Asthma & Allergies
16. ^ Jan F. Kreider. Handbook of heating, ventilation, and air conditioning. CRC press. ISBN 0849395844.
17. ^ Winnick, J (1996). Chemical engineering thermodynamics. John Wiley and Sons. ISBN 0471055905.
18. ^ Michigan Fast Facts and Trivia, retrieved on 2009-08-29.
19. ^ ^{a b} "Air Conditioning and Refrigeration Timeline", National Academy of Engineering, retrieved 2009-08-29.
20. ^ "Air Conditioning and Refrigeration History - part 4", National Academy of Engineering, retrieved 2009-08-29.
21. ^ Alder, Dennis (2004). Packard. MBI Publishing Company. p. 76. ISBN 9780760319284.
22. ^ The Great Lakelands (Lake Valley, Inc) 6: 32. 1956.
23. ^ Gunnell, John (1982). Standard catalog of American cars, 1946-1975. Krause Publications. p. 176.
24. ^ ^{a b} Al Binder and the Ward's staff, "Rearview Mirror", Ward's AutoWorld, 2001-02-01, retrieved on 2009-08-26.
25. ^ Daly, Steven (2006). Automotive Air-Conditioning and Climate Control Systems. Elsevier Science & Technology Books. p. 2. ISBN 9780750669559.
26. ^ Stevenson, Heon J. (2008). American Automobile Advertising, 1930-1980: An Illustrated History. McFarland & Company. p. 177. ISBN 9780786436859.
27. ^ "1953-1955 Nash and Hudson Ramblers" by the editors of Consumer Guide, 2007-11-29, retrieved on 2009-08-29.
28. ^ Nunney, Malcolm J. (2006). Light and Heavy Vehicle Technology. Elsevier Science & Technology Books. p. 147. ISBN 9780750680370.
29. ^ Nash, Gerald D. (1999). Federal Landscape: An Economic History of the Twentieth-Century West. University of Arizona Press. pp. 224. ISBN 9780816518630.
30. ^ Ward's automotive yearbook (Ward's Communications Inc.) 31: 116. 1969.
31. ^ "U.S. Business: Shuffle & Cut". Time. October 6. http://www.time.com/time/printout/0,8816,844040,00.html
32. ^ Common Heat Pumps
33. ^ ACCA home page

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