Central air conditioning system wikipedia

Central air conditioning system wikipedia DEFAULT

Central Air-Conditioning

Central air conditioning (or central A/C) is a system in which air is cooled at a central location and distributed to and from rooms by one or more fans and ductwork. The work of the air conditioner compressor is what makes the whole process of air conditioning possible. The compression of the refrigerant gas enables it to discharge heat out of the house, which is how the cool air is created.

Lennox® air conditioners 

Exacting precision makes Lennox® central air conditioners among the quietest and most energy-efficient units you can buy.

Types of central air conditioners

There are two types of central air conditioners: a split system or a packaged unit.

In a split-system central air conditioner, an outdoor metal cabinet contains the condenser and compressor, and an indoor cabinet contains the evaporator. In many split-system air conditioners, this indoor cabinet also contains a furnace or an air handler. The air conditioner's evaporator coil is installed in the cabinet or main supply duct of this furnace or heat pump. If your home already has a furnace but no air conditioner, a split system is the most economical central air conditioner to install.

In a packaged central air conditioner, the evaporator, condenser, and compressor are all located in one cabinet, which usually is placed on a roof or on a concrete slab next to the house's foundation. Air supply and return ducts come from indoors through the home's exterior wall or roof to connect with the packaged air conditioner, which is usually located outdoors. Packaged air conditioners often include electric heating coils or a natural gas furnace. This combination of air conditioner and central heater eliminates the need for a separate furnace indoors.

Benefits of a central air-conditioning system

  • Indoor comfort during warm weather – Central air conditioning helps keep your home cool and reduces humidity levels.
  • Cleaner air – As your central air-conditioning system draws air out of the rooms in your house through return air ducts, the air is pulled through an air filter, which removes airborne particles such as dust and lint. Sophisticated filters, like those found in the Lennox Healthy Climate® purification systems, may remove microscopic pollutants, as well. The filtered air is then routed to air supply ductwork that carries it back to the rooms.
  • Quieter operation – Because the compressor-bearing unit is located outside the home, the indoor noise level from its operation is much lower than that of a free-standing air- conditioning unit.

Lennox® air conditioners deliver efficiency and comfort

Exacting precision makes Lennox® air conditioners among the quietest and most energy-efficient units you can buy. Available with multi-stage and single-stage motors, Lennox air conditioners allow you to control cooling, humidity levels and energy use by matching output to demand. With industry-leading efficiencies of up to 26.00 SEER*, Lennox air conditioners can also save you hundreds of dollars in utility costs every year.

Explore the full selection of Lennox® Air Conditioners

*Efficiency claim based on comparison of air conditioning and heat pump products' SEER as published in AHRI (January 2015). Actual system combination efficiency may vary; consult AHRI for exact system efficiencies. Precision claim based on the cooling capacity range of the XC/XP25-036 units as compared to equivalent-sized competitive variable-capacity compressor units.

Sours: https://www.lennox.com

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Or maybe that approachability can be traced back to years of conditioning? Kinane has been the voice behind Comedy Central’s on-air announcements since 2011 … Maybe something from an entertainment …

A central heating system provides warmth to the whole interior of a building (or portion of a building) from one point to multiple rooms.When combined with other systems in order to control the building climate, the whole system may be an HVAC (heating, ventilation and air conditioning) system.

Central, "all-air" air-conditioning systems (or package systems) with a combined outdoor condenser/evaporator unit are often installed in North American residences, offices, and public buildings, but are difficult to retrofit (install in a building that was not designed to receive it) because of the bulky air ducts required.

Heating Air Conditioning System Reduce your heating and cooling costs by up to half with Solar-Ready Air Conditioners and heat pumps. packaged units choose Lennox® Packaged Units when you need a self-contained heating and cooling system that installs outside. some HVAC experts say your combined heating and cooling system should receive maintenance twice a year. Here are four jobs

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Mar 08, 2019  · Central air conditioning is a method of structural cooling in which a centralized unit cools and dehumidifies air before circulating it throughout a building. This is in direct contrast with systems that rely on individual units in rooms or suites of rooms.

A central air conditioner is either a split-system unit or a packaged unit. In a split-system central air conditioner, an outdoor metal cabinet contains the condenser and compressor, and an indoor cabinet contains the evaporator.

Central air conditioners circulate cool air through a system of supply and return ducts. Supply ducts and registers (i.e., openings in the walls, floors, or ceilings covered by grills) carry cooled air from the air conditioner to the home.

Hvac A An HVAC technician installs, maintains, and repairs heating, air conditioning, and refrigeration systems. HVAC is an abbreviation for "heating, ventilation, and air conditioning." An alternative but less common abbreviation is HVACR. LOWELL — Classrooms are sufficiently heated. That’s what city officials argued in a response to orders from the Department of Labor Standards. "Based on

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What Is An Hvac? Choosing an HVAC Training in Bangalore can be a difficult task since there are many present but before settling down for any HVAC Training in Bangalore you must be aware of what HVAC is all about. MOORESVILLE, N.C., March 25, 2019 /PRNewswire/ — The founders of TemperaturePro of the Carolinas, a Mooresville HVAC company, are

Types of Air Conditioning Systems: Window, Split, Packaged and Central HVAC: Heating, Ventilation & Air-Conditioning / By Haresh Khemani / Mechanical Engineering The choice of which air conditioner system to use depends upon a number of factors including how large the area is to be cooled, the total heat generated inside the enclosed area, etc.

I was taking the train from Noborito, where I lived, to Ginza, in central Tokyo to meet my lover … worse than the heat was …

Sours: https://www.dcrefrigerationandhvac.com/central-air-conditioning-wikipedia/
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Central Air Conditioning

Central air conditioners circulate cool air through a system of supply and return ducts. Supply ducts and registers (i.e., openings in the walls, floors, or ceilings covered by grills) carry cooled air from the air conditioner to the home. This cooled air becomes warmer as it circulates through the home; then it flows back to the central air conditioner through return ducts and registers. To learn how central air conditioners compare to other cooling systems, check out our Energy Saver 101 Infographic: Home Cooling.

Air conditioners dehumidify the air to improve comfort.  However, in extremely humid climates, when outdoor temperatures are moderate, or in cases where the air conditioner is oversized, the air may not reach a low enough humidity to achieve a comfortable level.  In those instances, homeowners may reduce the thermostat setting or use a dehumidifier.  But in both cases this will increase energy use, both for the dehumidifier itself and because the air conditioner will require more energy to cool the house. 

If you have a central air system in your home, set the fan to the "auto" mode. In other words, don't use the system's central fan to provide air circulation -- use circulating fans in individual rooms.

Types of Central Air Conditioners

A central air conditioner is either a split-system unit or a packaged unit.

In a split-system central air conditioner, an outdoor cabinet contains the outdoor heat exchanger, fan, and compressor, and an indoor cabinet contains the indoor heat exchanger and blower. In many split-system air conditioners, the indoor cabinet may contain the a furnace or the indoor heat exchanger of a heat pump. If your home already has a furnace but no air conditioner, a split-system may be the most economical central air conditioner to install.

In a packaged central air conditioner, the heat exchangers, compressor, fan, and blower are all located in one cabinet, which usually is placed on a roof or on a concrete slab next to the house's foundation. This type of air conditioner also is used in small commercial buildings. The supply and return ducts come from indoors through the home's exterior wall or roof to connect with the packaged air conditioner. Packaged air conditioners often include electric heating coils or a natural gas furnace. This combination of air conditioner and central heater eliminates the need for a separate furnace.

Choosing or Upgrading Your Central Air Conditioner

Central air conditioners are more efficient than room air conditioners. In addition, they are out of the way, quiet, and convenient to operate. To save energy and money, you should try to buy an energy-efficient air conditioner and reduce your central air conditioner's energy use. In an average size home, air conditioning consumes more than 2,000 kilowatt-hours of electricity per year, causing power plants to emit about 3,500 pounds of carbon dioxide and 31 pounds of sulfur dioxide.

If you are considering adding central air conditioning to your home, the deciding factor may be the need for ductwork.

The most efficient air conditioners use 30% to 50% less energy to produce the same amount of cooling as air conditioners made in the mid 1970s. Even if your air conditioner is only 10 years old, you may save 20% to 40% of your cooling energy costs by replacing it with a newer, more efficient model.

Proper sizing and installation are key elements in determining air conditioner efficiency. Too large a unit will not adequately remove humidity. Too small a unit will not be able to attain a comfortable temperature on the hottest days. Improper unit location, lack of insulation, and improper duct installation can greatly diminish efficiency.

When buying an air conditioner, look for a model with a high efficiency. Central air conditioners are rated according to their seasonal energy efficiency ratio (SEER). SEER indicates the relative amount of energy needed to provide a specific cooling output. Many newer systems have SEER ratings as high as 26.

If your air conditioner is old, consider buying an energy-efficient model. Look for the ENERGY STAR® and EnergyGuide labels -- qualified central units are about 15% more efficient than standard models. New residential central air conditioner standards went into effect on January 1, 2015; see the efficiency standards for central air conditioners for details, and consider purchasing a system with a higher SEER than the minimum for greater savings.

The standards do not require you to change your existing central air conditioning units, and replacement parts and services should still be available for your home's systems. The "lifespan" of a central air conditioner is about 15 to 20 years. Manufacturers typically continue to support existing equipment by making replacement parts available and honoring maintenance contracts after the new standard goes into effect.

Other features to look for when buying an air conditioner include:

  • A variable speed air conditioning system
  • A unit that operates quietly
  • A filter check light to remind you to check the filter after a predetermined number of operating hours
  • An automatic-delay fan switch to turn off the fan a few minutes after the compressor turns off.

Installation and Location of Air Conditioners

If your air conditioner is installed correctly, or if major installation problems are found and fixed, it should perform efficiently for years with only minor routine maintenance. However, many air conditioners are not installed correctly. As an unfortunate result, modern energy-efficient air conditioners can perform almost as poorly as older inefficient models.

When installing a new central air conditioning system, be sure that your contractor:

  • Allows adequate indoor space for the installation, maintenance, and repair of the new system
  • Uses a duct-sizing methodology such as the Air Conditioning Contractors of America (ACCA) Manual D
  • Ensures there are enough supply registers to deliver cool air and enough return air registers to carry warm house air back to the air conditioner
  • Installs duct work within the conditioned space, not in the attic, wherever possible
  • Seals all ducts with duct mastic and heavily insulates ducts
  • Locates the condensing unit where its noise will not keep you or your neighbors awake at night, if possible
  • Locates the condensing unit where no nearby objects will block airflow to it
  • Verifies that the newly installed air conditioner has the exact refrigerant charge and airflow rate specified by the manufacturer
  • Locates the thermostat away from heat sources, such as windows or supply registers.
Sours: https://www.energy.gov/energysaver/central-air-conditioning
HVAC:new central air conditioning installed in home

Air conditioning

Cooling of air in buildings or vehicles

This article is about cooling of air. For the Curved Air album, see Air Conditioning (album).

Air conditioning condenser units outside a building
Window mounted air conditioner for single room use

Air conditioning, often abbreviated as A/C or AC, is the process of removing heat and controlling the humidity of air in an enclosed space to achieve a more comfortable interior environment by use of powered "air conditioners" or a variety of other methods, including passive cooling and ventilative cooling. Air conditioning is a member of a family of systems and techniques that provide heating, ventilation, and air conditioning (HVAC).

Air conditioners, which typically use vapor-compression refrigeration, range in size from small units used within vehicles or single rooms to massive units that can cool large buildings.[1][2]Air source heat pumps, which can be used for heating as well as cooling, are becoming increasingly common in cooler climates.

According to the IEA, as of 2018, 1.6 billion air conditioning units were installed, which accounted for an estimated 20% of energy usage in buildings globally with the number expected to grow to 5.6 billion by 2050.[3] The United Nations called for the technology to be made more sustainable to mitigate climate change using techniques including passive cooling, evaporative cooling, selective shading, windcatchers and better thermal insulation. CFC and HCFC refrigerants such as R-12 and R-22, respectively, used within air conditioners have caused damage to the ozone layer, and HFC refrigerants such as R-410a and R-404a, which were designed to replace CFCs and HCFCs, are instead exacerbating climate change. Both issues happen due to venting of refrigerant to the atmosphere, such as during repairs. HFO refrigerants, used in some if not most new equipment, solve both issues with an ozone damage potential (ODP) of zero and a much lower global warming potential (GWP) in the single or double digits vs. the three or four digits of HFCs.

History[edit]

Air-conditioning dates back to prehistory. Ancient Egyptian buildings used a wide variety of passive air-conditioning techniques.[4] These became widespread from the Iberian Peninsula through North Africa, the Middle East, and Northern India.[5] Similar techniques were developed in hot climates elsewhere.[further explanation needed]

Passive techniques remained widespread until the 20th century, when they fell out of fashion, replaced by powered A/C. Using information from engineering studies of traditional buildings, passive techniques are being revived and modified for 21st-century architectural designs.[6][5]

An array of air conditioners outside a commercial office building

Air conditioners allow the building indoor environment to remain relatively constant largely independent of changes in external weather conditions and internal heat loads. They also allow deep plan buildings to be created and have allowed people to live comfortably in hotter parts of the world.[citation needed]

Development[edit]

Preceding discoveries[edit]

In 1558, Giambattista della Porta described a method of chilling ice to temperatures far below its freezing point by mixing it with potassium nitrate (then called "nitre") in his popular science book Natural Magic.[7][8][9] In 1620, Cornelis Drebbel demonstrated "Turning Summer into Winter" for James I of England, chilling part of the Great Hall of Westminster Abbey with an apparatus of troughs and vats.[10] Drebbel's contemporary Francis Bacon, like della Porta a believer in science communication, may not have been present at the demonstration, but in a book published later the same year, he described it as "experiment of artificial freezing" and said that "Nitre (or rather its spirit) is very cold, and hence nitre or salt when added to snow or ice intensifies the cold of the latter, the nitre by adding to its own cold, but the salt by supplying activity to the cold of the snow."[7]

In 1758, Benjamin Franklin and John Hadley, a chemistry professor at University of Cambridge, conducted an experiment to explore the principle of evaporation as a means to rapidly cool an object. Franklin and Hadley confirmed that the 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-in-glass thermometer as their object and with a bellows used to speed up the evaporation. They lowered the temperature of the thermometer bulb down to −14 °C (7 °F) while the ambient temperature was 18 °C (64 °F). Franklin noted that soon after they passed the freezing point of water 0 °C (32 °F), a thin film of ice formed on the surface of the thermometer's bulb and that the ice mass was about 6 mm (1⁄4 in) thick when they stopped the experiment upon reaching −14 °C (7 °F). Franklin concluded: "From this experiment one may see the possibility of freezing a man to death on a warm summer's day."[11]

The 19th century included a number of developments in compression technology. In 1820, English scientist and inventor Michael Faraday discovered that compressing and liquefying ammonia could chill air when the liquefied ammonia was allowed to evaporate.[12] 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. He hoped to eventually use his ice-making machine to regulate the temperature of buildings[12][13] and envisioned centralized air conditioning that could cool entire cities. Gorrie was granted a patent in 1851, but following the death of his main backer he was not able to realise his invention.[14] In 1851, James Harrison created the first mechanical ice-making machine in Geelong, Australia, and was granted a patent for an ether vapor-compression refrigeration system in 1855 that produced three tons of ice per day.[15] In 1860, Harrison established a second ice company and later entered the debate over how to compete against the American advantage of ice-refrigerated beef sales to the United Kingdom.[15]

First A/C devices[edit]

Willis Carrier, who is credited with building the first modern electrical air conditioning unit

Electricity made development of effective units possible. In 1901, American inventor Willis H. Carrier built what is considered the first modern electrical air conditioning unit.[16][17][18][19] In 1902, he installed his first air-conditioning system, in the Sackett-Wilhelms Lithographing & Publishing Company in Brooklyn, New York;[20] his invention controlled both the temperature and also the humidity which helped maintain consistent paper dimensions and ink alignment at the printing plant. Later, together with six other employees, Carrier formed The Carrier Air Conditioning Company of America, a business that in 2020 employed 53,000 employees and was valued at $18.6 billion.[21][22]

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 analogous 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.[23]

Domestic air conditioning soon took off. In 1914, the first domestic air conditioning was installed in Minneapolis in the home of Charles Gilbert Gates. It is however possible that the huge device (c. 7 x 6 x 20 ft) was never used, as the house remained uninhabited[12][24] (Gates had already died in October 1913).

In 1931, H.H. Schultz and J.Q. Sherman developed what would become the most common type of individual room air conditioner: one designed to sit on a window ledge. The units went on sale in 1932 at a considerable price (the equivalent of $120,000 to $600,000 in today's money.)[12] A year later the first air conditioning systems for cars systems were offered for sale.[25]Chrysler Motors introduced the first practical semi-portable air conditioning unit in 1935,[26] and Packard became the first automobile manufacturer to offer an air conditioning unit in its cars in 1939.[27]

Further development[edit]

Innovations in the latter half of the 20th century allowed for much more ubiquitous air conditioner use. In 1945, Robert Sherman of Lynn, Massachusetts invented a portable, in-window air conditioner that cooled, heated, humidified, dehumidified, and filtered the air.[28] By the late 1960s, most newly built residential homes in the United States had central air conditioning. Box air conditioning units during this time also became less expensive, which resulted in greater population growth in the states of Florida and Arizona.[citation needed]

As international development has increased wealth across countries, global use of air conditioners has increased. By 2018, an estimated 1.6 billion air conditioning units were installed worldwide,[29] with the International Energy Agency expecting this number to grow to 5.6 billion units by 2050.[3] Between 1995 and 2004, the proportion of urban households in China with air conditioners increased from 8% to 70%.[30] As of 2015, nearly 100 million homes, or about 87% of US households, had air conditioning systems.[31] In 2019, it was estimated that 90% of new single-family homes constructed in the USA included air conditioning (ranging from 99% in the South to 62% in the West).[32][33]

Types of air conditioner[edit]

Mini-split and multi-split systems[edit]

Evaporator, indoor unit, or terminal, side of a ductless split-type air conditioner

Ductless systems (often mini-split, though there are now ducted mini split) typically supply conditioned and heated air to a single or a few rooms of a building, without ducts and in a decentralized manner.[34] Multi-zone or multi-split systems are a common application of ductless systems and allow up to eight rooms (zones or locations) to be conditioned independently from each other, each with its own indoor unit and simultaneously from a single outdoor unit. The main problem with multi-split systems is the length of the refrigerant lines for connecting the external unit to the internal ones.[citation needed] Though the same challenge exists for central ACs.

The first mini-split systems were sold in 1954–1968 by Mitsubishi Electric and Toshiba in Japan, where its development was motivated by the small size of homes.[35][36][37] Multi-zone ductless systems were invented by Daikin in 1973, and variable refrigerant flow systems (which can be thought of as larger multi-split systems) were also invented by Daikin in 1982. Both were first sold in Japan.[38] Variable refrigerant flow systems when compared with central plant cooling from an air handler, eliminate the need for large cool air ducts, air handlers, and chillers; instead cool refrigerant is transported through much smaller pipes to the indoor units in the spaces to be conditioned, thus allowing for less space above dropped ceilings and a lower structural impact, while also allowing for more individual and independent temperature control of spaces, and the outdoor and indoor units can be spread across the building.[39] Variable refrigerant flow indoor units can also be turned off individually in unused spaces.[citation needed]

Ducted central systems[edit]

Split-system central air conditioners consist of two heat exchangers, an outside unit (the condenser) from which heat is rejected to the environment and an internal heat exchanger (the fan coil unit, air handling unit, or evaporator) with the piped refrigerant being circulated between the two. The FCU is then connected to the spaces to be cooled by ventilation ducts.[40]

Central plant cooling[edit]

See also: Chiller

Cooling towers used in a central chilled water plant using liquid-cooled chillers

Large central cooling plants may use intermediate coolant such as chilled water pumped into air handlers or fan coil units near or in the spaces to be cooled which then duct or deliver cold air into the spaces to be conditioned, rather than ducting cold air directly to these spaces from the plant, which is not done due to the low density and heat capacity of air which would require impractically large ducts. The chilled water is cooled by chillers in the plant, which use a refrigeration cycle to cool water, often transferring its heat to the atmosphere even in liquid-cooled chillers through the use of cooling towers. Chillers may be air or liquid-cooled.[citation needed]

Portable units[edit]

A portable system has an indoor unit on wheels connected to an outdoor unit via flexible pipes, similar to a permanently fixed installed unit (such as a central air conditioner).[citation needed]

Hose systems, which can be monoblock or air-to-air, 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. Such portable units draw indoor air and expel it outdoors through a single duct.[citation needed]

Many portable air conditioners come with heat as well as dehumidification function.[41]

Window unit and packaged terminal[edit]

Main article: Packaged terminal air conditioner

The packaged terminal air conditioner (PTAC), through-the-wall, and window air conditioners are similar. PTAC systems may be adapted to provide heating in cold weather, either directly by using an electric strip, gas, or other heaters, or by reversing the refrigerant flow to heat the interior and draw heat from the exterior air, converting the air conditioner into a heat pump. They may be installed in a wall opening with the help of a special sleeve on the wall and a custom grill that is flush with the wall and window air conditioners can also be installed in a window, but without a custom grill.[42]

Packaged air conditioner[edit]

Packaged air conditioners (also known as self-contained units)[43][44] are central systems that integrate into a single housing all the components of a split central system, and deliver air, possibly through ducts, to the spaces to be cooled. Depending on their construction they may be outdoors or indoors, on roofs (rooftop units),[45][46] draw the air to be conditioned from inside or outside a building and be water, refrigerant[47] or air-cooled. Often, outdoor units are air-cooled while indoor units are liquid-cooled using a cooling tower.[40][48][49][50][51][52]

Operation[edit]

Operating principles[edit]

Main article: Vapor-compression refrigeration

Cooling in traditional AC systems is accomplished using the vapor-compression cycle, which uses the forced circulation and phase change of a refrigerant between gas and liquid to transfer heat. The vapor-compression cycle can occur within a unitary, or packaged piece of equipment; or within a chiller that is connected to terminal cooling equipment (such as a fan coil unit in an air handler) on its evaporator side and heat rejection equipment such as a cooling tower on its condenser side. An air source heat pump shares many components with an air conditioning system, but includes a reversing valve which allows the unit to be used to heat as well as cool a space.[53]

Air conditioning equipment will reduce the absolute humidity of the air processed by the system if the surface of the evaporator coil is significantly cooler than the dew point of the surrounding air. An air conditioner designed for an occupied space will typically achieve a 30% to 60% relative humidity in the occupied space.[54]

Most modern air-conditioning systems feature a dehumidification cycle during which the compressor runs while the fan is slowed to reduce the evaporator temperature and therefore condense more water. A dehumidifier uses the same refrigeration cycle but incorporates both the evaporator and the condenser into the same air path; the air first passes over the evaporator coil where it is cooled[55] and dehumidified before passes over the condenser coil where it is warmed again before being released back into the room again.[citation needed]

Free cooling can sometimes be selected when the external air happens to be cooler than the internal air and therefore the compressor needs not be used, resulting in high cooling efficiencies for these times. This may also be combined with seasonal thermal energy storage.[56]

Heating[edit]

Main article: Heat pump

Some air conditioning systems have the option to reverse the refrigeration cycle and act as air source heat pump, therefore producing heating instead of cooling in the indoor environment. They are also commonly referred to as "reverse cycle air conditioners". The heat pump is significantly more energy efficient than electric resistance heating, because it moves energy from air or groundwater to the heated space, as well as the heat from purchased electrical energy. When the heat pump is in heating mode, the indoor evaporator coil switches roles and becomes the condenser coil, producing heat. The outdoor condenser unit also switches roles to serve as the evaporator and discharges cold air (colder than the ambient outdoor air).

Air-source heat pumps are more popular in milder winter climates where the temperature is frequently in the range of 4–13 °C (40–55 °F), because heat pumps become inefficient in more extreme cold. This is partly because ice forms on the outdoor unit's heat exchanger coil, which blocks airflow 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 condenser coil, so that it can heat up and defrost. Some heat pump systems will therefore 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 indoor air cooling, which would otherwise be uncomfortable in the winter.

The icing problem becomes much more severe with lower outdoor temperatures, so heat pumps are commonly installed in tandem with a more conventional form of heating, such as an electrical heater, a natural gas, Heating oil or wood-burning fireplace or central heating, 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.

Performance[edit]

Main articles: coefficient of performance, Seasonal energy efficiency ratio, and European seasonal energy efficiency ratio

The coefficient of performance (COP) of a air conditioning system is a ratio of useful heating or cooling provided to work required.[57][58] Higher COPs equate to lower operating costs. The COP usually exceeds 1; however, the exact value is highly dependent on operating conditions, especially absolute temperature and relative temperature between sink and system, and is often graphed or averaged against expected conditions.[59] Air conditioner equipment power in the U.S. is often described in terms of "tons of refrigeration," with each approximately equal to the cooling power of one short ton (2,000 pounds (910 kg) of ice melting in a 24-hour period. The value is equal to 12,000 BTUIT per hour, or 3,517 watts.[60] Residential central air systems are usually from 1 to 5 tons (3.5 to 18 kW) in capacity.[citation needed]

The efficiency of air conditioners is often rated by the seasonal energy efficiency ratio (SEER) which is defined by the Air Conditioning, Heating, and Refrigeration Institute in its 2008 standard AHRI 210/240, Performance Rating of Unitary Air-Conditioning and Air-Source Heat Pump Equipment.[61] A similar standard is the European seasonal energy efficiency ratio (ESEER).[citation needed]

Impact[edit]

Health effects[edit]

In hot weather, air conditioning can prevent heat stroke, dehydration from excessive perspiration, and other problems related to hyperthermia.[62]Heat waves are the most lethal type of weather phenomenon in developed countries. Air conditioning (including filtration, humidification, cooling and disinfection) can be used to provide a clean, safe, hypoallergenic atmosphere in hospital operating rooms and other environments where proper atmosphere is critical to patient safety and well-being. It is sometimes recommended for home use by people with allergies, especially mold.[citation needed]

Poorly maintained water cooling towers can promote the growth and spread of microorganisms such as Legionella pneumophila, the infectious agent responsible for Legionnaires' disease. As long as the cooling tower is kept clean (usually by means of a chlorine treatment), these health hazards can be avoided or reduced. The state of New York has codified requirements for registration, maintenance, and testing of cooling towers to protect against Legionella.[63]

Environmental impacts[edit]

Refrigerants have caused and continue to cause serious environmental issues, including ozone depletion and climate change, as several countries have not yet ratified the Kigali Amendment to reduce the consumption and production of hydrofluorocarbons.[64]

Current air conditioning accounts for 20% of energy consumption in buildings globally, and the expected growth of the usage of air conditioning due to climate change and technology uptake will drive significant energy demand growth.[65][66] Alternatives to continual air conditioning include passive cooling, passive solar cooling natural ventilation, operating shades to reduce solar gain, using trees, architectural shades, windows (and using window coatings) to reduce solar gain.[citation needed]

In 2018 the United Nations called for the technology to be made more sustainable to mitigate climate change.[67][68]

Economic effects[edit]

Air conditioning caused various shifts in demography, notably that of the United States starting from the 1970s:

  • The birth rate was lower in the spring than during other seasons until 1970s but this difference then declined over the next 30 years[69]
  • The summer mortality rate, which had been higher in regions subject to a heatwave during the summer, also evened out.[citation needed].
  • The Sun Belt now contains 30% of the total US population when it was inhabited by 24% of Americans at the beginning of the 20th century.[70]

First designed to benefit targeted industries such as the press as well as large factories, the invention quickly spread to public agencies and administrations with studies with claims of increased productivity close to 24% in places equipped with air conditioning.[71]

Other techniques[edit]

Buildings designed with passive air conditioning are generally less expensive to construct and maintain than buildings with conventional HVAC systems with lower energy demands.[72] While tens of air changes per hour, and cooling of tens of degrees, can be achieved with passive methods, site-specific microclimate must be taken into account, complicating building design.[5]

Many techniques can be used to increase comfort and reduce the temperature in buildings. These include evaporative cooling, selective shading, wind, thermal convection, and heat storage.[citation needed]

Passive ventilation[edit]

This section is an excerpt from Passive ventilation.[edit]

The ventilation system of a regular earthship.
Passive ventilationis the process of supplying air to and removing air from an indoor space without using mechanical systems. It refers to the flow of external air to an indoor space as a result of pressuredifferences arising from natural forces. There are two types of natural ventilationoccurring in buildings: wind driven ventilationand buoyancy-driven ventilation. Wind driven ventilation arises from the different pressures created by wind around a building or structure, and openings being formed on the perimeter which then permit flow through the building. Buoyancy-driven ventilation occurs as a result of the directional buoyancy force that results from temperature differences between the interior and exterior.[73]Since the internal heat gains which create temperature differences between the interior and exterior are created by natural processes, including the heat from people, and wind effects are variable, naturally ventilated buildings are sometimes called "breathing buildings".

Passive cooling[edit]

This section is an excerpt from Passive cooling.[edit]

A traditional Iraniansolar cooling design

Passive cooling is a building design approach that focuses on heat gain control and heat dissipation in a building in order to improve the indoor thermal comfort with low or no energy consumption.[74][75] This approach works either by preventing heat from entering the interior (heat gain prevention) or by removing heat from the building (natural cooling).[76]

Natural cooling utilizes on-site energy, available from the natural environment, combined with the architectural design of building components (e.g. building envelope), rather than mechanical systems to dissipate heat.[77] Therefore, natural cooling depends not only on the architectural design of the building but on how the site's natural resources are used as heat sinks (i.e. everything that absorbs or dissipates heat). Examples of on-site heat sinks are the upper atmosphere (night sky), the outdoor air (wind), and the earth/soil.

Passive cooling is an important tool for design of buildings for climate change adaptation – reducing dependency on energy-intensive air conditioning in warming environments.[78][79]
A pair of short windcatchersor malqafused in traditional architecture; wind is forced down on the windwardside and leaves on the leewardside (cross-ventilation). In the absence of wind, the circulation can be driven with evaporative cooling in the inlet (which is also designed to catch dust). In the center, a shuksheika(roof lanternvent), used to shade the qa'abelow while allowing hot air rise out of it (stack effect).[4]

Fans[edit]

Main article: Ceiling fan

Hand fans have existed since prehistory. Large human-powered fans built into buildings include the punkah.

The 2nd-century Chinese inventor Ding Huan of the Han Dynasty invented a rotary fan for air conditioning, with seven wheels 3 m (10 ft) in diameter and manually powered by prisoners.[80]: 99, 151, 233  In 747, Emperor Xuanzong (r. 712–762) of the Tang Dynasty (618–907) had the Cool Hall (Liang Dian涼殿) 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. During the subsequent Song Dynasty (960–1279), written sources mentioned the air conditioning rotary fan as even more widely used.[80]: 134, 151 

Thermal buffering[edit]

In areas which are cold at night or in winter, heat storage is used. Heat may be stored in earth or masonry; air is drawn past the masonry to heat or cool it.[6]

In areas which are below freezing at night in winter, snow and ice can be collected and stored in ice houses for later use in cooling.[6] This technique is over 3,700 years old in the Middle East.[81] Harvesting outdoor ice during winter and transporting and storing for use in summer was practiced by wealthy Europeans in the early 1600s,[7] and became popular in Europe and the Americas towards the end of the 1600s.[82] This practice was replaced by mechanical compression-cycle ice-making machines (see below).

Evaporative cooling[edit]

Main article: Evaporative cooler

In dry, hot climates, the evaporative cooling effect may be used by placing water at the air intake, such that the draft draws air over water and then into the house. For this reason, it is sometimes said that the fountain, in the architecture of hot, arid climates, is like the fireplace in the architecture of cold climates.[4] Evaporative cooling also makes the air more humid, which can be beneficial in a dry desert climate.[83]

Evaporative coolers tend to feel as if they are not working during times of high humidity, when there is not much dry air with which the coolers can work to make the air as cool as possible for dwelling occupants. Unlike other types of air conditioners, evaporative coolers rely on the outside air to be channeled through cooler pads that cool the air before it reaches the inside of a house through its air duct system; this cooled outside air must be allowed to push the warmer air within the house out through an exhaust opening such as an open door or window.[84]

See also[edit]

References[edit]

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Sours: https://en.wikipedia.org/wiki/Air_conditioning

Conditioning system air wikipedia central

Heating, ventilation, and air conditioning

Technology of indoor and vehicular environmental comfort

This article is about technology of indoor and vehicular environmental comfort. For high-voltage alternating current, see high-voltage alternating current. For efforts to reduce changes to Earth's climate (climate control), see Climate change mitigation.

Rooftop HVAC unit with view of fresh-air intake vent
The control circuit in a household HVAC installation. The wires connecting to the blue terminal block on the upper-right of the board lead to the thermostat. The fan enclosure is directly behind the board, and the filterscan be seen at the top. The safety interlockswitch is at the bottom left.

Heating, ventilation, and air conditioning (HVAC)[1] is the technology of indoor and vehicular environmental comfort. Its goal is to provide thermal comfort and acceptable indoor air quality. HVAC system design is a subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics and heat transfer. "Refrigeration" is sometimes added to the field's abbreviation, as HVAC&R or HVACR or "ventilation" is dropped, as in HACR (as in the designation of HACR-rated circuit breakers).

HVAC is an important part of residential structures such as single family homes, apartment buildings, hotels and senior living facilities, medium to large industrial and office buildings such as skyscrapers and hospitals, vehicles such as cars, trains, airplanes, ships and submarines, and in marine environments, where safe and healthy building conditions are regulated with respect to temperature and humidity, using fresh air from outdoors.

Ventilating or ventilation (the "V" in HVAC) is the process of exchanging or replacing air in any space to provide high indoor air quality which involves temperature control, oxygen replenishment, and removal of moisture, odors, smoke, heat, dust, airborne bacteria, carbon dioxide, and other gases. Ventilation removes unpleasant smells and excessive moisture, introduces outside air, keeps interior building air circulating, and prevents stagnation of the interior air.

Ventilation often refers to the intentional delivery of the outside air to the building indoor environment. It is one of the most important factors for maintaining acceptable indoor air quality in buildings. Methods for ventilating a building are divided into mechanical/forced and natural types.[2]

Overview[edit]

The three major functions of heating, ventilation, and air conditioning are interrelated, especially with the need to provide thermal comfort and acceptable indoor air quality within reasonable installation, operation, and maintenance costs. HVAC systems can be used in both domestic and commercial environments. HVAC systems can provide ventilation, and maintain pressure relationships between spaces. The means of air delivery and removal from spaces is known as room air distribution.[3]

Individual systems[edit]

See also: HVAC control system

In modern buildings, the design, installation, and control systems of these functions are integrated into one or more HVAC systems. For very small buildings, contractors normally estimate the capacity and type of system needed and then design the system, selecting the appropriate refrigerant and various components needed. For larger buildings, building service designers, mechanical engineers, or building services engineers analyze, design, and specify the HVAC systems. Specialty mechanical contractors and suppliers then fabricate, install and commission the systems. Building permits and code-compliance inspections of the installations are normally required for all sizes of building.

District networks[edit]

Although HVAC is executed in individual buildings or other enclosed spaces (like NORAD's underground headquarters), the equipment involved is in some cases an extension of a larger district heating (DH) or district cooling (DC) network, or a combined DHC network. In such cases, the operating and maintenance aspects are simplified and metering becomes necessary to bill for the energy that is consumed, and in some cases energy that is returned to the larger system. For example, at a given time one building may be utilizing chilled water for air conditioning and the warm water it returns may be used in another building for heating, or for the overall heating-portion of the DHC network (likely with energy added to boost the temperature).[4][5][6]

Basing HVAC on a larger network helps provide an economy of scale that is often not possible for individual buildings, for utilizing renewable energy sources such as solar heat,[7][8][9] winter's cold,[10][11] the cooling potential in some places of lakes or seawater for free cooling, and the enabling function of seasonal thermal energy storage. By utilizing natural sources that can be used for HVAC systems it can make a huge difference for the environment and help expand the knowledge of using different methods.

History[edit]

See also: Air conditioning § History

HVAC is based on inventions and discoveries made by Nikolay Lvov, Michael Faraday, Rolla C. Carpenter, Willis Carrier, Edwin Ruud, Reuben Trane, James Joule, William Rankine, Sadi Carnot, and many others.[12]

Multiple inventions within this time frame preceded the beginnings of first comfort air conditioning system, which was designed in 1902 by Alfred Wolff (Cooper, 2003) for the New York Stock Exchange, while Willis Carrier equipped the Sacketts-Wilhems Printing Company with the process AC unit the same year. Coyne College was the first school to offer HVAC training in 1899.[13]

The invention of the components of HVAC systems went hand-in-hand with the industrial revolution, and new methods of modernization, higher efficiency, and system control are constantly being introduced by companies and inventors worldwide.

Heating[edit]

Main article: Central heating

"Heater" redirects here. For other uses, see Heater (disambiguation).

Heaters are appliances whose purpose is to generate heat (i.e. warmth) for the building. This can be done via central heating. Such a system contains a boiler, furnace, or heat pump to heat water, steam, or air in a central location such as a furnace room in a home, or a mechanical room in a large building. The heat can be transferred by convection, conduction, or radiation. Space heaters are used to heat single rooms and only consist of a single unit.

Generation[edit]

Heaters exist for various types of fuel, including solid fuels, liquids, and gases. Another type of heat source is electricity, normally heating ribbons composed of high resistance wire (see Nichrome). This principle is also used for baseboard heaters and portable heaters. Electrical heaters are often used as backup or supplemental heat for heat pump systems.

The heat pump gained popularity in the 1950s in Japan and the United States.[14] Heat pumps can extract heat from various sources, such as environmental air, exhaust air from a building, or from the ground. Heat pumps transfer heat from outside the structure into the air inside. Initially, heat pump HVAC systems were only used in moderate climates, but with improvements in low temperature operation and reduced loads due to more efficient homes, they are increasing in popularity in cooler climates.

Distribution[edit]

Water/steam[edit]

In the case of heated water or steam, piping is used to transport the heat to the rooms. Most modern hot water boiler heating systems have a circulator, which is a pump, to move hot water through the distribution system (as opposed to older gravity-fed systems). The heat can be transferred to the surrounding air using radiators, hot water coils (hydro-air), or other heat exchangers. The radiators may be mounted on walls or installed within the floor to produce floor heat.

The use of water as the heat transfer medium is known as hydronics. The heated water can also supply an auxiliary heat exchanger to supply hot water for bathing and washing.

Air[edit]

Warm air systems distribute heated air through duct work systems of supply and return air through metal or fiberglass ducts. Many systems use the same ducts to distribute air cooled by an evaporator coil for air conditioning. The air supply is normally filtered through air filters to remove dust and pollen particles.[15]

Dangers[edit]

The use of furnaces, space heaters, and boilers as a method of indoor heating could result in incomplete combustion and the emission of carbon monoxide, nitrogen oxides, formaldehyde, volatile organic compounds, and other combustion byproducts. Incomplete combustion occurs when there is insufficient oxygen; the inputs are fuels containing various contaminants and the outputs are harmful byproducts, most dangerously carbon monoxide, which is a tasteless and odorless gas with serious adverse health effects.[16]

Without proper ventilation, carbon monoxide can be lethal at concentrations of 1000 ppm (0.1%). However, at several hundred ppm, carbon monoxide exposure induces headaches, fatigue, nausea, and vomiting. Carbon monoxide binds with hemoglobin in the blood, forming carboxyhemoglobin, reducing the blood's ability to transport oxygen. The primary health concerns associated with carbon monoxide exposure are its cardiovascular and neurobehavioral effects. Carbon monoxide can cause atherosclerosis (the hardening of arteries) and can also trigger heart attacks. Neurologically, carbon monoxide exposure reduces hand to eye coordination, vigilance, and continuous performance. It can also affect time discrimination.[17]

Ventilation[edit]

Main article: Ventilation (architecture)

Ventilation is the process of changing or replacing air in any space to control temperature or remove any combination of moisture, odors, smoke, heat, dust, airborne bacteria, or carbon dioxide, and to replenish oxygen. Ventilation often refers to the intentional delivery of the outside air to the building indoor space. It is one of the most important factors for maintaining acceptable indoor air quality in buildings. Methods for ventilating a building may be divided into mechanical/forced and natural types.[18]

Mechanical or forced[edit]

Further information: Ventilation (architecture) § Mechanical systems

HVAC ventilation exhaust for a 12-story building

Mechanical, or forced, ventilation is provided by an air handler (AHU) and used to control indoor air quality. Excess humidity, odors, and contaminants can often be controlled via dilution or replacement with outside air. However, in humid climates more energy is required to remove excess moisture from ventilation air.

Kitchens and bathrooms typically have mechanical exhausts to control odors and sometimes humidity. Factors in the design of such systems include the flow rate (which is a function of the fan speed and exhaust vent size) and noise level. Direct drive fans are available for many applications, and can reduce maintenance needs.

In summer, ceiling fans and table/floor fans circulate air within a room for the purpose of reducing the perceived temperature by increasing evaporation of perspiration on the skin of the occupants. Because hot air rises, ceiling fans may be used to keep a room warmer in the winter by circulating the warm stratified air from the ceiling to the floor.

Passive[edit]

Main article: Passive ventilation

Natural ventilation is the ventilation of a building with outside air without using fans or other mechanical systems. It can be via operable windows, louvers, or trickle vents when spaces are small and the architecture permits. ASHRAE defined Natural ventilation as the flow of air through open windows, doors, grilles, and other planned building envelopepenetrations, and as being driven by natural and/or artificially produced pressure differentials.[2]

In more complex schemes, warm air is allowed to rise and flow out high building openings to the outside (stack effect), causing cool outside air to be drawn into low building openings. Natural ventilation schemes can use very little energy, but care must be taken to ensure comfort. In warm or humid climates, maintaining thermal comfort solely via natural ventilation might not be possible. Air conditioning systems are used, either as backups or supplements. Air-side economizers also use outside air to condition spaces, but do so using fans, ducts, dampers, and control systems to introduce and distribute cool outdoor air when appropriate.

An important component of natural ventilation is air change rate or air changes per hour: the hourly rate of ventilation divided by the volume of the space. For example, six air changes per hour means an amount of new air, equal to the volume of the space, is added every ten minutes. For human comfort, a minimum of four air changes per hour is typical, though warehouses might have only two. Too high of an air change rate may be uncomfortable, akin to a wind tunnel which have thousands of changes per hour. The highest air change rates are for crowded spaces, bars, night clubs, commercial kitchens at around 30 to 50 air changes per hour.[19]

Room pressure can be either positive or negative with respect to outside the room. Positive pressure occurs when there is more air being supplied than exhausted, and is common to reduce the infiltration of outside contaminants.[20]

Airborne diseases[edit]

Natural ventilation [21] is a key factor in reducing the spread of airborne illnesses such as tuberculosis, the common cold, influenza, meningitis or COVID-19. Opening doors and windows are good ways to maximize natural ventilation, which would make the risk of airborne contagion much lower than with costly and maintenance-requiring mechanical systems. Old-fashioned clinical areas with high ceilings and large windows provide greatest protection. Natural ventilation costs little and is maintenance free, and is particularly suited to limited-resource settings and tropical climates, where the burden of TB and institutional TB transmission is highest. In settings where respiratory isolation is difficult and climate permits, windows and doors should be opened to reduce the risk of airborne contagion. Natural ventilation requires little maintenance and is inexpensive.[22]

Air conditioning[edit]

Main article: Air conditioning

An air conditioning system, or a standalone air conditioner, provides cooling and/or humidity control for all or part of a building. Air conditioned buildings often have sealed windows, because open windows would work against the system intended to maintain constant indoor air conditions. Outside, fresh air is generally drawn into the system by a vent into a mix air chamber for mixing with the space return air. Then the mixture air enters an indoor or outdoor heat exchanger section where the air is to be cooled down, then be guided to the space creating positive air pressure. The percentage of return air made up of fresh air can usually be manipulated by adjusting the opening of this vent. Typical fresh air intake is about 10% of the total supply air.[citation needed]

Air conditioning and refrigeration are provided through the removal of heat. Heat can be removed through radiation, convection, or conduction. The heat transfer medium is a refrigeration system, such as water, air, ice, and chemicals are referred to as refrigerants. A refrigerant is employed either in a heat pump system in which a compressor is used to drive thermodynamic refrigeration cycle, or in a free cooling system which uses pumps to circulate a cool refrigerant (typically water or a glycol mix).

It is imperative that the air conditioning horsepower is sufficient for the area being cooled. Underpowered air conditioning system will lead to power wastage and inefficient usage. Adequate horsepower is required for any air conditioner installed.

Refrigeration cycle[edit]

Main article: Heat pump and refrigeration cycle

The refrigeration cycle uses four essential elements to cool, which are compressor, condenser, metering device and evaporator.

  • At the inlet of a compressor, the refrigerant inside the system is in a low pressure, low temperature, gaseous state. The compressor pumps the refrigerant gas up to a high pressure and temperature.
  • From there it enters a heat exchanger (sometimes called a condensing coil or condenser) where it loses heat to the outside, cools, and condenses into its liquid phase.
  • An expansion valve (also called metering device) regulates the refrigerant liquid to flow at the proper rate.
  • The liquid refrigerant is returned to another heat exchanger where it is allowed to evaporate, hence the heat exchanger is often called an evaporating coil or evaporator. As the liquid refrigerant evaporates it absorbs heat from the inside air, returns to the compressor, and repeats the cycle. In the process, heat is absorbed from indoors and transferred outdoors, resulting in cooling of the building.

In variable climates, the system may include a reversing valve that switches from heating in winter to cooling in summer. By reversing the flow of refrigerant, the heat pump refrigeration cycle is changed from cooling to heating or vice versa. This allows a facility to be heated and cooled by a single piece of equipment by the same means, and with the same hardware.

Free cooling[edit]

Main article: Free cooling

Free cooling systems can have very high efficiencies, and are sometimes combined with seasonal thermal energy storage so that the cold of winter can be used for summer air conditioning. Common storage mediums are deep aquifers or a natural underground rock mass accessed via a cluster of small-diameter, heat-exchanger-equipped boreholes. Some systems with small storages are hybrids, using free cooling early in the cooling season, and later employing a heat pump to chill the circulation coming from the storage. The heat pump is added-in because the storage acts as a heat sink when the system is in cooling (as opposed to charging) mode, causing the temperature to gradually increase during the cooling season.

Some systems include an "economizer mode", which is sometimes called a "free-cooling mode". When economizing, the control system will open (fully or partially) the outside air damper and close (fully or partially) the return air damper. This will cause fresh, outside air to be supplied to the system. When the outside air is cooler than the demanded cool air, this will allow the demand to be met without using the mechanical supply of cooling (typically chilled water or a direct expansion "DX" unit), thus saving energy. The control system can compare the temperature of the outside air vs. return air, or it can compare the enthalpy of the air, as is frequently done in climates where humidity is more of an issue. In both cases, the outside air must be less energetic than the return air for the system to enter the economizer mode.

Packaged vis-à-vis split system[edit]

Central, "all-air" air-conditioning systems (or package systems) with a combined outdoor condenser/evaporator unit are often installed in North American residences, offices, and public buildings, but are difficult to retrofit (install in a building that was not designed to receive it) because of the bulky air ducts required.[23] (Minisplit ductless systems are used in these situations.) Outside of North America, packaged systems are only used in limited applications involving large indoor space such as stadiums, theatres or exhibition halls.

An alternative to packaged systems is the use of separate indoor and outdoor coils in split systems. Split systems are preferred and widely used worldwide except in North America. In North America, split systems are most often seen in residential applications, but they are gaining popularity in small commercial buildings. Split systems are used where ductwork is not feasible or where the space conditioning efficiency is of prime concern.[24] The benefits of ductless air conditioning systems include easy installation, no ductwork, greater zonal control, flexibility of control and quiet operation.[25] In space conditioning, the duct losses can account for 30% of energy consumption.[26] The use of minisplit can result in energy savings in space conditioning as there are no losses associated with ducting.

With the split system, the evaporator coil is connected to a remote condenser unit using refrigerant piping between an indoor and outdoor unit instead of ducting air directly from the outdoor unit. Indoor units with directional vents mount onto walls, suspended from ceilings, or fit into the ceiling. Other indoor units mount inside the ceiling cavity, so that short lengths of duct handle air from the indoor unit to vents or diffusers around the rooms.

Split systems are more efficient and the footprint is typically smaller than the package systems. On the other hand, package systems tend to have slightly lower indoor noise level compared to split system since the fan motor is located outside.

Dehumidification[edit]

Dehumidification (air drying) in an air conditioning system is provided by the evaporator. Since the evaporator operates at a temperature below the dew point, moisture in the air condenses on the evaporator coil tubes. This moisture is collected at the bottom of the evaporator in a pan and removed by piping to a central drain or onto the ground outside.

A dehumidifier is an air-conditioner-like device that controls the humidity of a room or building. It is often employed in basements which have a higher relative humidity because of their lower temperature (and propensity for damp floors and walls). In food retailing establishments, large open chiller cabinets are highly effective at dehumidifying the internal air. Conversely, a humidifier increases the humidity of a building.

Humidification[edit]

Main article: Humidifier

Maintenance[edit]

All modern air conditioning systems, even small window package units, are equipped with internal air filters. These are generally of a lightweight gauze-like material, and must be replaced or washed as conditions warrant. For example, a building in a high dust environment, or a home with furry pets, will need to have the filters changed more often than buildings without these dirt loads. Failure to replace these filters as needed will contribute to a lower heat exchange rate, resulting in wasted energy, shortened equipment life, and higher energy bills; low air flow can result in iced-over evaporator coils, which can completely stop air flow. Additionally, very dirty or plugged filters can cause overheating during a heating cycle, and can result in damage to the system or even fire.

Because an air conditioner moves heat between the indoor coil and the outdoor coil, both must be kept clean. This means that, in addition to replacing the air filter at the evaporator coil, it is also necessary to regularly clean the condenser coil. Failure to keep the condenser clean will eventually result in harm to the compressor, because the condenser coil is responsible for discharging both the indoor heat (as picked up by the evaporator) and the heat generated by the electric motor driving the compressor.

Energy efficiency[edit]

HVAC is significantly responsible for promoting energy efficiency of buildings as the building sector consumes the largest percentage of global energy.[27] Since the 1980s, manufacturers of HVAC equipment have been making an effort to make the systems they manufacture more efficient. This was originally driven by rising energy costs, and has more recently been driven by increased awareness of environmental issues. Additionally, improvements to the HVAC system efficiency can also help increase occupant health and productivity.[28] In the US, the EPA has imposed tighter restrictions over the years. There are several methods for making HVAC systems more efficient.

Heating energy[edit]

In the past, water heating was more efficient for heating buildings and was the standard in the United States. Today, forced air systems can double for air conditioning and are more popular.

Some benefits of forced air systems, which are now widely used in churches, schools and high-end residences, are

  • Better air conditioning effects
  • Energy savings of up to 15-20%
  • Even conditioning[citation needed]

A drawback is the installation cost, which can be slightly higher than traditional HVAC systems.

Energy efficiency can be improved even more in central heating systems by introducing zoned heating. This allows a more granular application of heat, similar to non-central heating systems. Zones are controlled by multiple thermostats. In water heating systems the thermostats control zone valves, and in forced air systems they control zone dampers inside the vents which selectively block the flow of air. In this case, the control system is very critical to maintaining a proper temperature.

Forecasting is another method of controlling building heating by calculating demand for heating energy that should be supplied to the building in each time unit.

Ground source heat pump[edit]

Main article: Geothermal heat pump

Ground source, or geothermal, heat pumps are similar to ordinary heat pumps, but instead of transferring heat to or from outside air, they rely on the stable, even temperature of the earth to provide heating and air conditioning. Many regions experience seasonal temperature extremes, which would require large-capacity heating and cooling equipment to heat or cool buildings. For example, a conventional heat pump system used to heat a building in Montana's −57 °C (−70 °F) low temperature or cool a building in the highest temperature ever recorded in the US—57 °C (134 °F) in Death Valley, California, in 1913 would require a large amount of energy due to the extreme difference between inside and outside air temperatures. A metre below the earth's surface, however, the ground remains at a relatively constant temperature. Utilizing this large source of relatively moderate temperature earth, a heating or cooling system's capacity can often be significantly reduced. Although ground temperatures vary according to latitude, at 1.8 metres (6 ft) underground, temperatures generally only range from 7 to 24 °C (45 to 75 °F).

Ventilation energy recovery[edit]

Energy recovery systems sometimes utilize heat recovery ventilation or energy recovery ventilation systems that employ heat exchangers or enthalpy wheels to recover sensible or latent heat from exhausted air. This is done by transfer of energy to the incoming outside fresh air.

Air conditioning energy[edit]

The performance of vapor compression refrigeration cycles is limited by thermodynamics.[29] These air conditioning and heat pump devices move heat rather than convert it from one form to another, so thermal efficiencies do not appropriately describe the performance of these devices. The Coefficient of performance (COP) measures performance, but this dimensionless measure has not been adopted. Instead, the Energy Efficiency Ratio (EER) has traditionally been used to characterize the performance of many HVAC systems. EER is the Energy Efficiency Ratio based on a 35 °C (95 °F) outdoor temperature. To more accurately describe the performance of air conditioning equipment over a typical cooling season a modified version of the EER, the Seasonal Energy Efficiency Ratio (SEER), or in Europe the ESEER, is used. SEER ratings are based on seasonal temperature averages instead of a constant 35 °C (95 °F) outdoor temperature. The current industry minimum SEER rating is 14 SEER.[30] Engineers have pointed out some areas where efficiency of the existing hardware could be improved. For example, the fan blades used to move the air are usually stamped from sheet metal, an economical method of manufacture, but as a result they are not aerodynamically efficient. A well-designed blade could reduce electrical power required to move the air by a third.[31]

Demand controlled kitchen ventilation[edit]

Main article: Demand controlled ventilation

Demand controlled kitchen ventilation (DCKV) is a building controls approach of controlling the volume of kitchen exhaust and supply air in response to the actual cooking loads in a commercial kitchen. Traditional commercial kitchen ventilation systems operate at 100% fan speed independent of the volume of cooking activity and DCKV technology changes that to provide significant fan energy and conditioned air savings. By deploying smart sensing technology, both the exhaust and supply fans can be controlled to capitalize on the affinity laws for motor energy savings, reduce makeup air heating and cooling energy, increasing safety and reducing ambient kitchen noise levels.[32]

Air filtration and cleaning[edit]

Main article: Air filter

Air cleaning and filtration removes particles, contaminants, vapors and gases from the air. The filtered and cleaned air then is used in heating, ventilation and air conditioning. Air cleaning and filtration should be taken in account when protecting our building environments.[33]

Clean air delivery rate (CADR) is the amount of clean air an air cleaner provides to a room or space. When determining CADR, the amount of airflow in a space is taken into account. For example, an air cleaner with a flow rate of 30 cubic metres (1,000 cu ft) per minute and an efficiency of 50% has a CADR of 15 cubic metres (500 cu ft) per minute. Along with CADR, filtration performance is very important when it comes to the air in our indoor environment. This depends on the size of the particle or fiber, the filter packing density and depth and the air flow rate.[33]

Industry and standards[edit]

The HVAC industry is a worldwide enterprise, with roles including operation and maintenance, system design and construction, equipment manufacturing and sales, and in education and research. The HVAC industry was historically regulated by the manufacturers of HVAC equipment, but regulating and standards organizations such as HARDI, ASHRAE, SMACNA, ACCA, Uniform Mechanical Code, International Mechanical Code, and AMCA have been established to support the industry and encourage high standards and achievement. (UL as an omnibus agency is not specific to the HVAC industry.)

The starting point in carrying out an estimate both for cooling and heating depends on the exterior climate and interior specified conditions. However, before taking up the heat load calculation, it is necessary to find fresh air requirements for each area in detail, as pressurization is an important consideration.

International[edit]

ISO 16813:2006 is one of the ISO building environment standards.[34] It establishes the general principles of building environment design. It takes into account the need to provide a healthy indoor environment for the occupants as well as the need to protect the environment for future generations and promote collaboration among the various parties involved in building environmental design for sustainability. ISO16813 is applicable to new construction and the retrofit of existing buildings.[35]

The building environmental design standard aims to:[35]

  • provide the constraints concerning sustainability issues from the initial stage of the design process, with building and plant life cycle to be considered together with owning and operating costs from the beginning of the design process;
  • assess the proposed design with rational criteria for indoor air quality, thermal comfort, acoustical comfort, visual comfort, energy efficiency and HVAC system controls at every stage of the design process;
  • iterate decisions and evaluations of the design throughout the design process.

United States[edit]

Main article: American Society of Heating, Refrigerating and Air-Conditioning Engineers

In the United States, HVAC engineers generally are members of the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE), EPA Universal CFC certified (for installation and service of CFC HVAC devices), or locally engineer certified such as a Special to Chief Boilers License issued by the state or, in some jurisdictions, the city. ASHRAE is an international technical society for all individuals and organizations interested in HVAC. The Society, organized into regions, chapters, and student branches, allows exchange of HVAC knowledge and experiences for the benefit of the field's practitioners and the public. ASHRAE provides many opportunities to participate in the development of new knowledge via, for example, research and its many technical committees. These committees typically meet twice per year at the ASHRAE Annual and Winter Meetings. A popular product show, the AHR Expo, has been held in conjunction with each winter ASHRAE meeting. The Society has approximately 50,000 members and has headquarters in Atlanta, Georgia.

The most recognized standards for HVAC design are based on ASHRAE data. The four volumes of most popular ASHRAE Handbooks are Fundamentals, Refrigeration, HVAC Applications and HVAC Systems and Equipment. The current versions of the four handbooks are shown below:[36]

  • 2020 ASHRAE Handbook—HVAC Systems and Equipment
  • 2019 ASHRAE Handbook—HVAC Applications
  • 2018 ASHRAE Handbook—Refrigeration
  • 2017 ASHRAE Handbook—Fundamentals

Each volume of the ASHRAE Handbook is updated every four years. The Fundamentals Handbook includes heating and cooling calculations. The design professional must consult ASHRAE data for the standards of design and care as the typical building codes provide little to no information on HVAC design practices; codes such as the UMC and IMC do include much detail on installation requirements, however. Other useful reference materials include items from SMACNA, ACGIH, and technical trade journals.

American design standards are legislated in the Uniform Mechanical Code or International Mechanical Code. In certain states, counties, or cities, either of these codes may be adopted and amended via various legislative processes. These codes are updated and published by the International Association of Plumbing and Mechanical Officials (IAPMO) or the International Code Council (ICC) respectively, on a 3-year code development cycle. Typically, local building permit departments are charged with enforcement of these standards on private and certain public properties.

Technicians[edit]

An HVAC technician is a tradesman who specializes in heating, ventilation, air conditioning, and refrigeration. HVAC technicians in the US can receive training through formal training institutions, where most earn associate degrees. Training for HVAC technicians includes classroom lectures and hands-on tasks, and can be followed by an apprenticeship wherein the recent graduate works alongside a professional HVAC technician for a temporary period.[citation needed] HVAC techs who have been trained can also be certified in areas such as air conditioning, heat pumps, gas heating, and commercial refrigeration.[37]

United Kingdom[edit]

The Chartered Institution of Building Services Engineers is a body that covers the essential Service (systems architecture) that allow buildings to operate. It includes the electrotechnical, heating, ventilating, air conditioning, refrigeration and plumbing industries. To train as a building services engineer, the academic requirements are GCSEs (A-C) / Standard Grades (1-3) in Maths and Science, which are important in measurements, planning and theory. Employers will often want a degree in a branch of engineering, such as building environment engineering, electrical engineering or mechanical engineering. To become a full member of CIBSE, and so also to be registered by the Engineering Council UK as a chartered engineer, engineers must also attain an Honours Degree and a master's degree in a relevant engineering subject.[citation needed] CIBSE publishes several guides to HVAC design relevant to the UK market, and also the Republic of Ireland, Australia, New Zealand and Hong Kong. These guides include various recommended design criteria and standards, some of which are cited within the UK building regulations, and therefore form a legislative requirement for major building services works. The main guides are:

  • Guide A: Environmental Design
  • Guide B: Heating, Ventilating, Air Conditioning and Refrigeration
  • Guide C: Reference Data
  • Guide D: Transportation systems in Buildings
  • Guide E: Fire Safety Engineering
  • Guide F: Energy Efficiency in Buildings
  • Guide G: Public Health Engineering
  • Guide H: Building Control Systems
  • Guide J: Weather, Solar and Illuminance Data
  • Guide K: Electricity in Buildings
  • Guide L: Sustainability
  • Guide M: Maintenance Engineering and Management

Within the construction sector, it is the job of the building services engineer to design and oversee the installation and maintenance of the essential services such as gas, electricity, water, heating and lighting, as well as many others. These all help to make buildings comfortable and healthy places to live and work in. Building Services is part of a sector that has over 51,000 businesses and employs represents 2%-3% of the GDP.

Australia[edit]

The Air Conditioning and Mechanical Contractors Association of Australia (AMCA), Australian Institute of Refrigeration, Air Conditioning and Heating (AIRAH), Australian Refrigeration Mechanical Association and CIBSE are responsible.

Asia[edit]

Asian architectural temperature-control have different priorities than European methods. For example, Asian heating traditionally focuses on maintaining temperatures of objects such as the floor or furnishings such as Kotatsu tables and directly warming people, as opposed to the Western focus, in modern periods, on designing air systems.

Philippines[edit]

The Philippine Society of Ventilating, Air Conditioning and Refrigerating Engineers (PSVARE) along with Philippine Society of Mechanical Engineers (PSME) govern on the codes and standards for HVAC / MVAC (MVAC means "mechanical ventilation and air conditioning") in the Philippines.

India[edit]

The Indian Society of Heating, Refrigerating and Air Conditioning Engineers (ISHRAE) was established to promote the HVAC industry in India. ISHRAE is an associate of ASHRAE. ISHRAE was founded at New Delhi[38] in 1981 and a chapter was started in Bangalore in 1989. Between 1989 & 1993, ISHRAE chapters were formed in all major cities in India.[citation needed]

See also[edit]

References[edit]

  1. ^"HVAC". Merriam–Webster Dictionary.
  2. ^ abVentilation and Infiltration chapter, Fundamentals volume of the ASHRAE Handbook, ASHRAE, Inc., Atlanta, GA, 2005
  3. ^Designer's Guide to Ceiling-Based Air Diffusion, Rock and Zhu, ASHRAE, Inc., New York, 2002
  4. ^Rezaie, Behnaz; Rosen, Marc A. (2012). "District heating and cooling: Review of technology and potential enhancements". Applied Energy. 93: 2–10. doi:10.1016/j.apenergy.2011.04.020.
  5. ^Werner S. (2006). ECOHEATCOOL (WP4) Possibilities with more district heating in Europe. Euroheat & Power, Brussels.Archived 2015-09-24 at the Wayback Machine
  6. ^Dalin P., Rubenhag A. (2006). ECOHEATCOOL (WP5) Possibilities with more district cooling in Europe, final report from the project. Final Rep. Brussels: Euroheat & Power.Archived 2012-10-15 at the Wayback Machine
  7. ^Nielsen, Jan Erik (2014). Solar District Heating Experiences from Denmark. Energy Systems in the Alps - storage and distribution … Energy Platform Workshop 3, Zurich - 13/2 2014
  8. ^Wong B., Thornton J. (2013). Integrating Solar & Heat Pumps. Renewable Heat Workshop.
  9. ^Pauschinger T. (2012). Solar District Heating with Seasonal Thermal Energy Storage in GermanyArchived 2016-10-18 at the Wayback Machine. European Sustainable Energy Week, Brussels. 18–22 June 2012.
  10. ^"How Renewable Energy Is Redefining HVAC | AltEnergyMag". www.altenergymag.com. Retrieved 2020-09-29.
  11. ^""Lake Source" Heat Pump System". HVAC-Talk: Heating, Air & Refrigeration Discussion. Retrieved 2020-09-29.
  12. ^Swenson, S. Don (1995). HVAC: heating, ventilating, and air conditioning. Homewood, Illinois: American Technical Publishers. ISBN .
  13. ^"History of Heating, Air Conditioning & Refrigeration". Coyne College.
  14. ^Iain Staffell, Dan Brett, Nigel Brandon and Adam Hawkes (30 May 2014). "A review of domestic heat pumps".CS1 maint: multiple names: authors list (link)
  15. ^"Furnace Filter Airflow - What You Need To Know? - HVAC BOSS". hvac-boss.com. Retrieved 2021-09-12.
  16. ^Bearg, David W. (1993). Indoor Air Quality and HVAC Systems. New York: Lewis Publishers. pp. 107–112.
  17. ^Dianat, Nazari, I,I. "Characteristic of unintentional carbon monoxide poisoning in Northwest Iran- Tabriz". International Journal of Injury Control and Promotion. Retrieved 2011-11-15.
  18. ^Ventilation and Infiltration chapter, Fundamentals volume of the ASHRAE Handbook, ASHRAE, Inc., Atlanta, Georgia, 2005
  19. ^"Air Change Rates for typical Rooms and Buildings". The Engineering ToolBox. Retrieved 2012-12-12.
  20. ^Bell, Geoffrey. "Room Air Change Rate". A Design Guide for Energy-Efficient Research Laboratories. Retrieved 2011-11-15.
  21. ^"Natural Ventilation for Infection Control in Health-Care Settings"(PDF). World Health Organization (WHO), 2009. Retrieved 2021-07-05.
  22. ^Escombe, A. R.; Oeser, C. C.; Gilman, R. H.; et al. (2007). "Natural ventilation for the prevention of airborne contagion". PLOS Med. 4 (68): e68. doi:10.1371/journal.pmed.0040068. PMC 1808096. PMID 17326709.
  23. ^"What are Air Ducts? The Homeowner's Guide to HVAC Ductwork". Retrieved 2018-05-14.
  24. ^"Ductless Mini-Split Heat Pumps". U.S. Department of Energy.
  25. ^"The Pros and Cons of Ductless Mini Split Air Conditioners". Retrieved 9 September 2020.
  26. ^"Ductless Mini-Split Air Conditioners". Retrieved 29 November 2019.
  27. ^Chenari, B., Dias Carrilho, J. and Gameiro da Silva, M., 2016. Towards sustainable, energy-efficient and healthy ventilation strategies in buildings: A review. Renewable and Sustainable Energy Reviews, 59, pp.1426-1447.
  28. ^"Sustainable Facilities Tool: HVAC System Overview". sftool.gov. Retrieved 2 July 2014.
  29. ^"Heating and Air Conditioning". www.nuclear-power.net. Retrieved 2018-02-10.
  30. ^"What Does SEER Stand For?". www.airrepairpros.com. 2015-09-07. Retrieved 2015-09-07.
  31. ^Keeping cool and green, The Economist 17 July 2010, p. 83
  32. ^"Technology Profile: Demand Control Kitchen Ventilation (DCKV)"(PDF). Retrieved 2018-12-04.
  33. ^ abHoward, J (2003), Guidance for Filtration and Air-Cleaning Systems to Protect Building Environments from Airborne Chemical, Biological, or Radiological Attacks, National Institute for Occupational Safety and Health, doi:10.26616/NIOSHPUB2003136, 2003-136
  34. ^ISO. "Building environment standards". www.iso.org. Retrieved 2011-05-14.
  35. ^ abISO. "Building environment design—Indoor environment—General principles". Retrieved 14 May 2011.
  36. ^"ASHRAE Handbook Online". www.ashrae.org. Retrieved 2020-06-17.
  37. ^"Certification basics/101". NATE. Archived from the original on 2011-10-06. Retrieved 2013-07-10.
  38. ^"About ISHRAE". ISHRAE. Retrieved 2021-10-11.

Further reading[edit]

External links[edit]

Sours: https://en.wikipedia.org/wiki/Heating,_ventilation,_and_air_conditioning
Mini Splits vs. Central Air Conditioners Compared - Sylvane
GDM AC.jpg

Central air conditioners circulate cool air through a system of supply and return ducts. Supply ducts and registers (i.e., openings in the walls, floors, or ceilings covered by grills) carry cooled air from the air conditioner to the home. This cooled air becomes warmer as it circulates through the home; then it flows back to the central air conditioner through return ducts and registers.

Air conditioners help to dehumidify the incoming air, but in extremely humid climates or in cases where the air conditioner is oversized, it may not achieve a low humidity. Running a dehumidifier in your air conditioned home will increase your energy use, both for the dehumidifier itself and because the air conditioner will require more energy to cool your house. A preferable alternative is ade humidifying heat pipe, which can be added as a retrofit to most existing systems.

Types of Central Air Conditioners[]

A central air conditioner is either a split-system unit or a packaged unit.

In a split-system central air conditioner, an outdoor metal cabinet contains the condenser and compressor, and an indoor cabinet contains the evaporator. In many split-system air conditioners, this indoor cabinet also contains a furnace or the indoor part of a heat pump. The air conditioner's evaporator coil is installed in the cabinet or main supply duct of this furnace or heat pump. If your home already has a furnace but no air conditioner, a split-system is the most economical central air conditioner to install.

In a packaged central air conditioner, the evaporator, condenser, and compressor are all located in one cabinet, which usually is placed on a roof or on a concrete slab next to the house's foundation. This type of air conditioner also is used in small commercial buildings. Air supply and return ducts come from indoors through the home's exterior wall or roof to connect with the packaged air conditioner, which is usually located outdoors. Packaged air conditioners often include electric heating coils or a natural gas furnace. This combination of air conditioner and central heater eliminates the need for a separate furnace indoors.

Installation and Location Air Conditioner []

If your air conditioner is installed correctly, or if major installation problems are found and fixed, it will perform efficiently for years with only minor routine maintenance. However, many air conditioners are not installed correctly. As an unfortunate result, modern energy-efficient air conditioners can perform almost as poorly as older inefficient models.

When installing a new central air conditioning system, be sure that your contractor:

  • Allows adequate indoor space for the installation, maintenance, and repair of the new system, and installs an access door in the furnace or duct to provide a way to clean the evaporator coil
  • Uses a duct-sizing methodology such as the Air Conditioning Contractors of America (ACCA)Manual D
  • Ensures there are enough supply registers to deliver cool air and enough return air registers to carry warm house air back to the air conditioner
  • Installs duct work within the conditioned space, not in the attic, wherever possible
  • Seals all ducts with duct mastic and heavily insulates attic ducts
  • Locates the condensing unit where its noise will not keep you or your neighbors awake at night, if possible
  • Locates the condensing unit where no nearby objects will block airflow to it
  • Verifies that the newly installed air conditioner has the exact refrigerant charge and airflow rate specified by the manufacturer
  • Locates the thermostat away from heat sources, such as windows or supply registers.

If you are replacing an older or failed split system, be sure that the evaporator coil is replaced with a new one that exactly matches the condenser coil in the new condensing unit. (The air conditioner's efficiency will likely not improve if the existing evaporator coil is left in place; in fact, the old coil could cause the new compressor to fail prematurely.)

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Air conditioner

The external section of a generic single-room air conditioning unit. For ease of the installation, units are typically fitted into windows or, as in this photograph, a hole in the wall
The internal section of the same unit. The front panel swings down to reveal the controls.
Note:the term "air conditioning" refers to any form of "Heating, ventilation and air-conditioning". This article deals specifically with units used as part of a cooling system.

An air conditioner is a system or a machine that treats air in a defined, usually enclosed area via a refrigeration cycle in which warm air is removed and replaced with cooler air.

In construction, a complete system of heating, ventilation, and air conditioning is referred to as HVAC. Whether in homes, offices or vehicles, its purpose is to provide comfort by altering the properties of the air, usually by cooling the air inside.The main function of air conditioner is to change adverse temperature.

History[change | change source]

In the 19th century Britishscientist and inventorMichael Faraday discovered that compressing and liquefying ammonia could chill air when the liquefied ammonia was allowed to evaporate.

In 1842, American physician Dr. John Gorrie used compressor technology to create ice, which he used to cool air for his patients.[1] He hoped eventually to use his ice-making machine to regulate the temperature of buildings and even considered cooling entire cities with a system of centralized air conditioning units.

Air conditioning applications[change | change source]

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 preferred by humans despite changes in external weather conditions or in internal heat loads.

Process applications aim to provide a suitable environment for an industrial or a commercial process, regardless of internal heat loads and external weather conditions. Although often in the same comfort range, it is the requirements of  the process that determines conditions, not human preference. Process applications include:

  • Hospital operating rooms in which air is filtered to high levels to reduce the risk of infection  and the humidity is 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 and pharmaceuticals  etc. in which extremely 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 which  mirror spring-like conditions can cause them to reproduce all year round.
  • Aircraft air conditioning. Although nominally aimed at providing comfort for passengers and the cooling of equipment, aircraft air conditioning presents a special process due to the low air pressure outside the aircraft.

Other examples include:

  • 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, the objective is not only to control temperature (although in some comfort applications this is all that is controlled) but also factors like humidity, air movement and air quality.

Air conditioning system basics and theories[change | change source]

Refrigeration cycle[change | change source]

A simple stylized diagram of the refrigeration cycle: 1) condensing coil, 2) expansion valve, 3) evaporator coil, 4) compressor.

In the refrigeration cycle, a pump transfers heat from a lower temperature source into a higher temperature heat sink. Heat will naturally flow in the opposite direction. This is the most common type of air conditioning. A refrigerated air conditioning system works in much the same way pumping heat out of the room in which it stands.

This cycle takes advantage of the universal gas lawPV = nRT, where P is pressure, V is volume, R is the universal gas constant, T is temperature, and n is the number of molecules of gas (1 mole = 6.022×1023 molecules).

The most common refrigeration cycle uses an electric motor to drive a 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 coolant around an enclosed system. The cooling liquid, or refrigerant is pumped into the cooled compartment (the evaporator coil). Low pressure then causes the refrigerant to evaporate taking the heat with it. In the other compartment (the condenser), the refrigerant vapour is compressed and forced through another heat exchange coil, condensed into a liquid which then rejects the heat previously absorbed from the cooled space.

Health implications[change | change source]

Air conditioning has as much influence on human health as any generic heating system.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.[2] Air conditioning can have a positive effect on sufferers of allergies and asthma.[3]

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

Installation of the conditioner[change | change source]

One of the main conditions for the high-quality installation of HVAC equipment is the correct choice of the fixing location of the indoor and outdoor units. Each of the listed modules is distinguished by certain design characteristics, rules for future installation. To install an air conditioner, you need to take into account all the requirements thanks to which the equipment can be further operated in different modes.

You need to install an air conditioner, given the following nuances:

  • A heavy outdoor unit is not fixed to walls made of aerated concrete;
  • Fasteners on the ventilated part of the facade are using a damping seal. The choice of this particular material is due to the fact that it reduces noise vibration during operation of the external unit;
  • Fixing the support brackets is carried out directly to the wall, and not to the decorative lining or insulation.

The installation of an air conditioner depends on certain criteria, it starts with finding the ideal site for mounting the outdoor unit. To do this, there are several recommendations:

  • The external unit is necessarily in the area of free circulation of air flows.
  • It is important to organize free access for further maintenance and repair of the unit.
  • During operation, exhausted streams of hot air come from the equipment, therefore it must be positioned so that the fumes do not enter the windows of the lower floors.[4]

References[change | change source]

Related pages[change | change source]

Other websites[change | change source]

Energy Efficiency[change | change source]

Archived 2006-04-10 at the Wayback Machine

Sours: https://simple.wikipedia.org/wiki/Air_conditioner


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