The term air conditioning refers to the cooling and dehumidification 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 (ASHRAE Standard 55 In a broader sense, the term can refer to any form of cooling, heating, ventilation or disinfection that modifies the condition of air. HVAC (pronounced either "H-V-A-C" or occasionally " H-vak " is an Initialism or Acronym that stands for " Heating Disinfectants are Antimicrobial agents that are applied to non-living objects to destroy Microorganisms, the process of which is known as disinfection. ^[1] An air conditioner (AC or A/C in North American English, aircon in British and Australian English) is an appliance, system, or mechanism 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 but sometimes using evaporation, most commonly for comfort cooling in buildings and motor vehicles. An air conditioner is an Appliance, System, or mechanism designed to extract Heat from an area via a Refrigeration cycle System (from Latin systēma, in turn from Greek systēma is a set of interacting or interdependent Entities, real or abstract Thermodynamic heat pump and refrigeration cycles are the models for Heat pumps and Refrigerators. Evaporative coolers (also called swamp, desert, or air coolers) are devices that cool air through the simple Evaporation of water

The concept of air conditioning is known to have been applied in Ancient Rome, where aqueduct water was circulated through the walls of certain houses to cool them. 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 An aqueduct is an artificial channel that is constructed to convey water from one location to another Similar techniques in medieval Persia involved the use of cisterns and wind towers to cool buildings during the hot season. The Persian Empire was a series of Iranian empires that ruled over the Iranian plateau, the original Persian homeland and beyond in Western Asia For cisterns in Neuroanatomy, see Cistern (neuroanatomy.For the village in England see Syston. A windcatcher ( Persian: بادگیر Bâdgir, Arabic: بارجيل Baarjiil) is a traditional Persian architectural device Modern air conditioning emerged from advances in chemistry during the 19th century, and the first large-scale electrical air conditioning was invented and used in 1902 by Willis Haviland Carrier. Chemistry (from Egyptian kēme (chem meaning "earth") is the Science concerned with the composition structure and properties Willis Haviland Carrier ( November 26, 1876 – October 7, 1950) was an Engineer and Inventor, and is known as the

Contents 1 History 2 Air conditioning applications 3 Humidity control 4 Health implications 5 Energy use 6 Portable air conditioners 7 Heat pumps 8 Professional bodies 8.1 American Society of Heating, Refrigerating, and Air-Conditioning Engineers 8.2 Australian Institute of Refrigeration Air Conditioning and Heating 9 See also 10 References

History

While moving heat via machinery to provide air conditioning is a relatively modern invention, the cooling of buildings is not. The ancient Romans were known to circulate aqueduct water through the walls of certain houses to cool them. 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 An aqueduct is an artificial channel that is constructed to convey water from one location to another As this sort of water usage was expensive, generally only the wealthy could afford such a luxury.

The 2nd century Chinese inventor Ding Huan (fl. China ( Wade-Giles ( Mandarin) Chung¹kuo² is a cultural region, an ancient Civilization, and depending on perspective a National 180) of the Han Dynasty invented a rotary fan for air conditioning, with seven wheels 3 m (10 ft) in diameter and manually powered. The Han Dynasty ( 206 BC–220 AD followed the Qin Dynasty and preceded the Three Kingdoms in China. A mechanical fan is an electrically powered device used to produce an airflow for the purpose of creature comfort (particularly in the heat ventilation, exhaust ^[2] In 747, Emperor Xuanzong (r. Emperor Xuanzong of Tang ( ( September 8, 685 Background Li Longji was born at the Tang Dynasty eastern capital Luoyang 712–762) of the Tang Dynasty (618–907) had the Cool Hall (Liang Tian) built in the imperial palace, which the Tang Yulin describes as having water-powered fan wheels for air conditioning as well as rising jet streams of water from fountains. The Tang Dynasty ( Middle Chinese: dhɑng (June 18 618&ndashJune 4 907 was an imperial dynasty of China preceded by the Sui Dynasty and followed by For the mechanical technology see Hydraulic machinery and Hydraulic cylinder Hydraulics is a topic of science and Engineering ^[3] During the subsequent Song Dynasty (960–1279), written sources mentioned the air conditioning rotary fan as even more widely used. The Song Dynasty ( Wade-Giles: Sung Ch'ao was a ruling dynasty in China between 960&ndash1279 CE it succeeded the Five Dynasties and Ten Kingdoms ^[4]

Medieval Persia had buildings that used cisterns and wind towers to cool buildings during the hot season: cisterns (large open pools in a 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. The Persian Empire was a series of Iranian empires that ruled over the Iranian plateau, the original Persian homeland and beyond in Western Asia For cisterns in Neuroanatomy, see Cistern (neuroanatomy.For the village in England see Syston. A windcatcher ( Persian: بادگیر Bâdgir, Arabic: بارجيل Baarjiil) is a traditional Persian architectural device ^[5] Cistern water evaporated, cooling the air in the building.

Ventilators were invented in medieval Egypt and were widely used in many houses throughout Cairo during the Middle Ages. Ventilation is the intentional movement of Air from outside a building to the inside 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 Cairo () which means "the Vanquisher" or "the Triumphant" is the capital and largest city of Egypt. These ventilators were later described in detail by Abd al-Latif al-Baghdadi in 1200, who reported that almost every house in Cairo has a ventilator, and that they cost anywhere from 1 to 500 dinars depending on their sizes and shapes. Abd-al-latif, Abd-el-latif or Abd-ul-Latif (1162 &ndash 1231 also known as al-Baghdadi ( Arabic, عبداللطيف البغدادي The Dinar is the name of the official currency in several countries Most ventilators in the city were oriented towards the Qibla, as was the city in general. Qiblah ( ar قبلة, also transliterated as Kiblah) is an Arabic word for the direction that should be faced when a Muslim prays during ^[6]

In 1820, British scientist and inventor Michael Faraday discovered that compressing and liquefying ammonia could chill air when the liquefied ammonia was allowed to evaporate. The United Kingdom of Great Britain and Ireland was the formal name of the United Kingdom from 1 January 1801 until 12 April 1927 An inventor is a person who creates or discovers a new method form device or other useful means Michael Faraday, FRS ( September 22 1791 – August 25 1867) was an English Ammonia is a compound with the formula N[[hydrogen H3]] It is normally encountered as a Gas with a characteristic pungent Odor In 1842, Florida physician John Gorrie used compressor technology to create ice, which he used to cool air for his patients in his hospital in Apalachicola, Florida. Florida ( is a state located in the southeastern region of the United States, bordering Alabama to the northwest and Georgia to the John Gorrie, ( October 3, 1802 &ndash June 29, 1855) physician scientist inventor and humanitarian is considered the father of ^[7] 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. ^[8] 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, for his failure, suspecting that Tudor had launched a smear campaign against his invention. Frederic Tudor ( September 4, 1783 - February 6, 1864) was Boston 's "Ice King" the founder of the Tudor Ice Company 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 Dr. Gorrie died impoverished in 1855 and the idea of air conditioning faded away for 50 years.

Early commercial applications of air conditioning were manufactured to cool air for industrial processing rather than personal comfort. In 1902 the first modern electrical air conditioning was invented by Willis Haviland Carrier. An invention is a new form composition of matter device or Process. Willis Haviland Carrier ( November 26, 1876 – October 7, 1950) was an Engineer and Inventor, and is known as the Designed to improve manufacturing process control in a printing plant, his invention controlled not only temperature but also humidity. Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature Humidity is the amount of water vapor in the air In daily language the term "humidity" is normally taken to mean Relative humidity. 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. The Carrier Corporation is the world’s largest manufacturer and distributor of heating ventilating and air conditioning ( HVAC) systems and a global leader in the commercial Over time air conditioning came to be used to improve comfort in homes and automobiles. Residential sales expanded dramatically in the 1950s.

In 1906, Stuart W. Cramer of Charlotte, North Carolina, USA, was exploring ways to add moisture to the air in his textile mill. The United States of America —commonly referred to as the 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. Evaporative coolers (also called swamp, desert, or air coolers) are devices that cool air through the simple Evaporation of water

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. A refrigerator (often called a " fridge " for short is a cooling appliance comprising a thermally insulated compartment and a Heat pump - Ammonia is a compound with the formula N[[hydrogen H3]] It is normally encountered as a Gas with a characteristic pungent Odor Chloromethane, also called Methyl chloride, R-40 or HCC 40 is a Chemical compound of the group of Organic compounds called Haloalkanes. Propane is a three- Carbon Alkane, normally a gas but compressible to a liquid that is transportable Thomas Midgley, Jr. created the first chlorofluorocarbon gas, Freon, in 1928. Thomas Midgley Jr ( May 18, 1889 – November 2, 1944) was an American mechanical engineer turned Chemist Freon is DuPont 's trade name for its odorless colorless nonflammable and noncorrosive Chlorofluorocarbon and Hydrochlorofluorocarbon Refrigerants The refrigerant was much safer for humans but was later found to be harmful to the atmosphere's ozone layer. The photochemical mechanisms that give rise to the ozone layer were worked out by the British physicist Sidney Chapman in 1930 Freon is a trademark name of 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-134). A trademark or trade mark, represented by the symbols ™ and ®, or mark is a distinctive sign or indicator used by an individual E I du Pont de Nemours and Company (,) is an American chemical company that was founded in July 1802 as a Gunpowder mill by Eleuthère Irénée The haloalkanes (also known as halogenoalkanes or alkyl halides) are a group of Chemical compounds consisting of Alkanes such as Methane The haloalkanes (also known as halogenoalkanes or alkyl halides) are a group of Chemical compounds consisting of Alkanes such as Methane The haloalkanes (also known as halogenoalkanes or alkyl halides) are a group of Chemical compounds consisting of Alkanes such as Methane 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-134. R-11 and R-12 are no longer manufactured in the US, the only source for 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, known by the brand name Puron. R-410A, sold under the trademarked names Puron, Genetron R410A, and AZ-20, is a near- azeotropic mixture of Difluoromethane (CH2F2

Innovation in air conditioning technologies continue, with much recent emphasis placed on energy efficiency and improving indoor air quality. Indoor Air Quality (IAQ deals with the content of interior air that could affect health and comfort of building occupants As an alternative to conventional refrigerants, natural alternatives like CO₂ (R-744) have been proposed. Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single ^[9]

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. Building indoor environment covers the environmental aspects in the design analysis and operation of energy-efficient healthy and comfortable buildings Human thermal comfort is defined by ASHRAE as the state of mind that expresses satisfaction with the surrounding environment (ASHRAE Standard 55

The highest performance for tasks performed by people seated in an office is expected to occur at 72 °F (22 °C) Performance is expected to degrade about 1% for every 2 °F change in room temperature. ^[10] The highest performance for tasks performed while standing is expected to occur at slightly lower temperatures. The highest performance for tasks performed by larger people is expected to occur at slightly lower temperatures. The highest performance for tasks performed by smaller people is expected to occur at slightly higher temperatures. Although generally accepted, some dispute that thermal comfort enhances worker productivity, as is described in the Hawthorne effect. The Hawthorne effect is a form of reactivity, and describes a temporary change to behavior or performance in response to a change in the environmental conditions with the response

Comfort air conditioning makes deep plan buildings feasible. A deep plan Building is a building in which the horizontal distance from the external Wall is many times greater than the Floor to floor height Without air conditioning, buildings must be built narrower or with light wells so that inner spaces receive sufficient outdoor air via natural ventilation. Natural ventilation is the process of supplying and removing air through an indoor space by natural means Air conditioning also allows buildings to be taller since wind speed increases significantly with altitude making natural ventilation impractical for very tall buildings. In common usage wind gradient, more specifically wind speed gradient or wind velocity gradient,or alternatively shear wind,is the vertical 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 comfort in a wide variety of transportation including 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. An operating theater (or theatre) was a tiered Theater or Amphitheater in which students and other spectators could watch surgeons perform surgery An infection is the detrimental Colonization of a host Organism by a foreign Species. 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). Cardiac surgery is Surgery on the Heart and/or Great vessels performed by a Cardiac surgeon.

• 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. A cleanroom is an environment typically used in Manufacturing or scientific research that has a low level of environmental Pollutants such as dust airborne Microchipsjpg|right|thumb|200px|Microchips ( EPROM memory with a transparent window showing the integrated circuit inside A drug, broadly speaking is any chemical substance that when absorbed into the body

• Facilities for breeding laboratory animals. Animal testing or animal research is the use of non-human Animals in scientific experimentation. 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
• 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, air motion, and air movement from space to space. Textile manufacturing is one of the oldest human industries The oldest known Textiles date back to about 5000 B Nuclear power is any Nuclear technology designed to extract usable Energy from atomic nuclei via controlled Nuclear reactions Chemistry (from Egyptian kēme (chem meaning "earth") is the Science concerned with the composition structure and properties Foundations of modern biology There are five unifying principles A laboratory (informally lab) is a facility that provides controlled conditions in which scientific Research, Experiments and Mining is the extraction of valuable Minerals or other geological materials from the earth usually (but not always from an Ore body Industrial Ecology (IE is an interdisciplinary field that focuses on the sustainable combination of environment, Economy and Technology. Cooking is the process of preparing Food by applying Heat, selecting measuring and combining of ingredients in an ordered procedure for producing safe and edible Food processing is the set of methods and techniques used to transform raw Ingredients into Food or to transform food into other forms for consumption by Humidity is the amount of water vapor in the air In daily language the term "humidity" is normally taken to mean Relative humidity.

Humidity control

Refrigeration air conditioning equipment usually reduces the humidity of the air processed by the system. Humidity is the amount of water vapor in the air In daily language the term "humidity" is normally taken to mean Relative humidity. 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. The dew point (sometimes spelled dewpoint) is the Temperature to which a given parcel of Air must be cooled at constant Barometric pressure, 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. Evaporation is the process by which Molecules in a Liquid state (e 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 a Household appliance that reduces the level of Humidity in air usually for health reasons as humid air can cause Mold and 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. Thermodynamic heat pump and refrigeration cycles are the models for Heat pumps and Refrigerators. 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 consequenses-- 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.

Ironically, unlike a regular air conditioner, a dehumidifier will actually heat a room just as an electric heater that draws the same amount of electricity (watts) as the dehumidifier. Electric heating is any process in which electrical energy is converted to heat The watt (symbol W) is the SI derived unit of power, equal to one Joule of energy per Second. 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. In Thermodynamics, a thermodynamic system, originally called a working substance, is defined as that part of the universe that is under consideration 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 electricity that is consumed by the dehumidifier is energy that is input into the thermodynamic system (the room), and remains in the room (as heat).

Dehumidifiers are commonly used in cold, damp climates to prevent mold growth indoors, especially in basements. WikipediaManual_of_Style#National_varieties_of_English --> Molds (or 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).

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. Legionella pneumophila is a thin pleomorphic, Flagellated Gram-negative bacterium of the genus Legionella. Legionellosis is an Infectious disease caused by Bacteria belonging to the Genus Legionella. Actinobacteria or actinomycetes are a group of Gram-positive bacteria with high G+C ratio. ^[11] 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. Hypoallergenic is a term coined by advertisers (based on the Greek prefix Hypo meaning "below normal" or "slightly" and first used in a cosmetics Air conditioning can have a positive effect on sufferers of allergies and asthma. Allergy is a disorder of the Immune system often also referred to as Atopy. Asthma is a chronic Condition involving the Respiratory system in which the airways occasionally constrict become inflamed, and are ^[12]

In serious heat waves, air conditioning can save the lives of the elderly. A heat wave is a prolonged period of excessively hot Weather, which may be accompanied by high Humidity. Some local authorities even set up public cooling centers for the benefit of those without air conditioning at home. A cooling center is a temporary air-conditioned Public space set up by local authorities to deal with the health effects of a Heat wave.

Poorly operating air conditioning systems can generate sound levels that contribute to hearing loss, if exposures are endured over a long term. These levels are similar to the exposure of living near a busy highway or airport for a considerable length of time. Properly functioning air conditioners are much quieter.

Energy use

It should be noted that 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 increase . A Closed system is a System in the state of being isolated from the environment 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) requires the air conditioner to remove that energy. In order to do that the air conditioner must increase its consumption by the inverse of its efficiency times the input unit 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 watts to compensate for this, thus making the 100 W light bulb utilise a total of 150 W of energy.

Note that it is typical for air conditioners to operate at "efficiencies" of significantly greater than 100%, see Coefficient of performance. The coefficient of performance, or COP (sometimes CP of a Heat pump is the ratio of the change in Heat at the "output" (the heat reservoir of interest

Portable air conditioners

A portable air conditioner or portable A/C is an air conditioner on wheels that can be easily transported inside a home or office. They are currently available with capacities of about 6,000 to 60,000 BTU/h (1,800 to 18,000 watts output) and with and without electric resistance heaters. Portable true air conditioners come in two forms, split and hose. HOSE (aka SHOE is a term used for playing a mixed game of Poker consisting of four different poker games Evaporative coolers, sometimes called conditioners, are also portable.

Air-cooled portable air conditioners are compressor-based refrigerant system that use air to exchange heat, in hte same way as a car or typical household air conditioner. With this type of system the air is dehumidified as it is cooled. They collect water condensed from the cooled air, and produce hot air which must be vented outside of the cooled area (they transfer heat from the air in the cooled area to air which must be vented).

A 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 and Monoblock, are vented to the outside via air ducts. Ducts are used in heating ventilation and air conditioning ( HVAC) to deliver and remove air The "monoblock" version collects the water in a bucket or tray and stops when full. The Air-to-Air version 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 run on approximately 1 to 3 ratio i. e. , to produce 3 kW of cooling this will use 1 kW of electricity. 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.

As a rule of thumb, 400 square feet (37 m²) can be cooled per 12,000 BTU/h (3. 5 kW or one ton of air conditioning) by a refrigerative air conditioner. However, other factors will affect the total heat load.

Evaporative air coolers, sometimes called air conditioners, do not have a compressor or condenser. Evaporative coolers (also called swamp, desert, or air coolers) are devices that cool air through the simple Evaporation of water Instead liquid water is evaporated, 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. The enthalpy of vaporization, (symbol \Delta{}_{v}H also known as the heat of vaporization or heat of evaporation, is the Energy required Disadvantages are that unless ambient humidity is low (dry climate) cooling is limited and the cooled air is very humid and can feel clammy. Humidity is the amount of water vapor in the air In daily language the term "humidity" is normally taken to mean Relative humidity. Climate encompasses the temperatures humidity rainfall atmospheric particle count and numerous other meteorogical factors in a given region over long periods of They have the advantage of needing no hoses to vent heat outside the cooled area, making them truly portable; and they are cheaper to install and use much less energy than true air conditioners.

Heat pumps

In thermodynamics a heat pump is a device which uses energy to transfer heat from a cooler to a hotter location. In Physics, thermodynamics (from the Greek θερμη therme meaning " Heat " and δυναμις dynamis meaning " A heat pump is a machine or device that moves Heat from one location (the 'source' to another location (the 'sink' or 'heat sink' using work. In Physics, heat, symbolized by Q, is Energy transferred from one body or system to another due to a difference in Temperature Strictly speaking a standard air conditioner is a unidirectional heat pump which moves heat only from a cool interior to a hotter exterior.

A type of air conditioner in which the refrigeration cycle can be reversed, warming the interior by extracting heat from the cooler exterior, is sometimes called a heat pump. Thermodynamic heat pump and refrigeration cycles are the models for Heat pumps and Refrigerators. Using a reversible air conditioner to heat the interior in this way is significantly more efficient than electric resistance heating. Electric heating is any process in which electrical energy is converted to heat When the heat pump function is enabled, the indoor evaporator coil switches roles and becomes the condensor coil, producing heat, while the outdoor condensor unit becomes the evaporator, venting 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 when ice forms on the outdoor unit's coil, blocking air flow. To compensate for this, a heat pump system in a cold climate 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 used this way will also need electric resistance heating in the indoor air path in this mode to compensate for the temporary air conditioning, which would otherwise cool the interior. The icing problem becomes worse 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 in very cold weather. Natural gas is a Gaseous Fossil fuel consisting primarily of Methane but including significant quantities of Ethane, Propane, Heating oil, or oil heat, also known in the United States as No A furnace is a device used for Heating The name derives from Latin fornax, Oven. 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.

Some more expensive window air conditioning units have the heat pump function. However, a window unit with a "heat" option is not necessarily a heat pump because some such units use electric resistance heating. 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. It is based out of the town of Washington D. C.

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.

See also

• Air conditioner
• Alliance for CO2 Solutions
• Energy conservation
• Evaporative cooler and Evaporative cooling
• Heat pump
• HVAC (and HVACR)
• Refrigeration
• Room air distribution
• Steam jet cooling

References

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