Cramer of Charlotte was exploring ways to add moisture to the air in his textile mill. Cramer coined the term "air conditioning", using it in a patent claim he filed that year as an analogue to "water conditioning", then a well-known process for making textiles easier to process. He combined moisture with ventilation to "condition" and change the air in the factories, controlling the humidity so necessary in textile plants.
Willis Carrier adopted the term and incorporated it into the name of his company. Shortly thereafter, the first private home to have air conditioning was built in Minneapolis in , owned by Charles Gates. Pierre DuBose designed a network of ductwork and vents for his home Meadowmont , all disguised behind intricate and attractive Georgian-style open moldings.
In , Robert Sherman of Lynn, Massachusetts invented a portable, in-window air conditioner that cooled, heated, humidified, dehumidified, and filtered the air. The first air conditioners and refrigerators employed toxic or flammable gases, such as ammonia , methyl chloride , or propane , that could result in fatal accidents when they leaked.
Thomas Midgley, Jr. The refrigerant names include a number indicating the molecular composition e.
The blend most used in direct-expansion home and building comfort cooling is an HCFC known as chlorodifluoromethane R Dichlorodifluoromethane R was the most common blend used in automobiles in the U. R and R are no longer manufactured in the U. Modern refrigerants have been developed to be more environmentally safe than many of the early chlorofluorocarbon-based refrigerants used in the early- and mid-twentieth century. Moreover, policy and political influence by corporate executives resisted change. The environmental organization Greenpeace provided funding to a former East German refrigerator company to research an alternative ozone- and climate-safe refrigerant in The company developed a hydrocarbon mix of isopentane and isobutane , but as a condition of the contract with Greenpeace could not patent the technology, which led to its widespread adoption by other firms.
In , Germany made CFC refrigerators illegal. EPA, disparaging the approach as "that German technology". 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 variable refrigerant flow terminal or fan coil unit on its evaporator side and heat rejection equipment on its condenser side.
In very dry climates, evaporative coolers, sometimes referred to as swamp coolers or desert coolers, are popular for improving coolness during hot weather.
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An evaporative cooler is a device that draws outside air through a wet pad, such as a large sponge soaked with water. The sensible heat of the incoming air, as measured by a dry bulb thermometer , is reduced. The temperature of the incoming air is reduced, but it is also more humid, so the total heat sensible heat plus latent heat is unchanged.
Some of the sensible heat of the entering air is converted to latent heat by the evaporation of water in the wet cooler pads. If the entering air is dry enough, the results can be quite substantial. Evaporative coolers tend to feel as if they are not working during times of high humidity, when there is not much dry air with which the coolers can work to make the air as cool as possible for dwelling occupants. Unlike other types of air conditioners, evaporative coolers rely on the outside air to be channeled through cooler pads that cool the air before it reaches the inside of a house through its air duct system; this cooled outside air must be allowed to push the warmer air within the house out through an exhaust opening such as an open door or window.
Air conditioning can also be provided by a process called free cooling which uses pumps to circulate a coolant such as air, water, or a water- glycol mixture from a cold source, which in turn acts as a heat sink for the energy that is removed from the cooled space. Common storage media are cool outside air, deep aquifers, or a natural underground rock mass accessed via a cluster of small-diameter boreholes. Some systems with small storage capacity are hybrid systems, using free cooling early in the cooling season, and later employing a heat pump to chill the circulation coming from the storage.
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The heat pump is added because the temperature of the storage gradually increases during the cooling season, thereby declining its effectiveness. Free cooling systems can have very high efficiencies, and are sometimes combined with seasonal thermal energy storage STES so the cold of winter can be used for summer air conditioning. Free cooling and hybrid systems are mature technology. Since humans perspire to provide natural cooling by the evaporation of perspiration from the skin, reducing relative humidity can promote occupant comfort.
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 dewpoint of the surrounding air. Moisture from the air will condense on the coil and must be disposed of or recycled. Most modern air-conditioning systems feature a dehumidification cycle during which the compressor runs while the fan is slowed as much as possible [ citation needed ] to reduce the evaporator temperature and therefore condense more water.
When the temperature falls below a threshold, both the fan and compressor are shut off to mitigate further temperature drops; [ clarification needed ] this prevents moisture on the evaporator from being blown back into the room.
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Occasionally, to thaw any ice produced, the fan runs with the compressor shut down; this function is less effective when ambient temperatures are low. Inverter air conditioners use the inside coil temperature sensor to keep the evaporator as cold as possible.
When the evaporator is too cold, [ clarification needed ] the compressor is slowed or stopped with the indoor fan running. A specialized air conditioner that is used only for dehumidifying is called a dehumidifier. It also uses a refrigeration cycle , but differs from a standard air conditioner in that both the evaporator and the condenser are placed in the same air path. A standard air conditioner transfers heat energy out of the room because its condenser coil releases heat outside. However, since all components of the dehumidifier are in the same room, no heat energy is removed.
Instead, the electric power consumed by the dehumidifier remains in the room as heat, so the room is actually heated , just as by an electric heater that draws the same amount of power. In addition, if water is condensed in the room, the amount of heat previously needed to evaporate that water also is re-released in the room the latent heat of vaporization.
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The dehumidification process is the inverse of adding water to the room with an evaporative cooler , and instead releases heat. Therefore, an in-room dehumidifier always will warm the room and reduce the relative humidity indirectly, as well as reducing the humidity directly by condensing and removing water. Inside the unit, the air passes over the evaporator coil first, and is cooled and dehumidified.
The now dehumidified, cold air then passes over the condenser coil where it is warmed up again. Then the air is released back into the room. The unit produces warm, dehumidified air and can usually be placed freely in the environment room that is to be conditioned. Dehumidifiers are commonly used in cold, damp climates to prevent mold growth indoors, especially in basements.
They are also used to protect sensitive equipment from the adverse effects of excessive humidity in tropical countries. In a thermodynamically closed system , any power dissipated into the system that is being maintained at a set temperature which is a standard mode of operation for modern air conditioners requires that the rate of energy removal by the air conditioner increase. This increase has the effect that, for each unit of energy input into the system say to power a light bulb in the closed system , the air conditioner removes that energy.
Air conditioner equipment power in the U. The value is defined as 12, BTU per hour, or watts. For residential homes, some countries set minimum requirements for energy efficiency. In the United States, the efficiency of air conditioners is often but not always rated by the seasonal energy efficiency ratio SEER. The higher the SEER rating, the more energy efficient is the air conditioner. The electrical energy consumed per year can be calculated as the average power multiplied by the annual operating time:. Assuming hours of operation during a typical cooling season i.
The EER is the efficiency rating for the equipment at a particular pair of external and internal temperatures, while SEER is calculated over a whole range of external temperatures i. The COP is a ratio with the same metric units of energy joules in both the numerator and denominator. They cancel out, leaving a dimensionless quantity. The United States now requires that residential systems manufactured in have a minimum SEER rating of 13 although window-box systems are exempt from this law, so their SEER is still around Window unit air conditioners are installed in an open window.
The interior air is cooled as a fan blows it over the evaporator. On the exterior the heat drawn from the interior is dissipated into the environment as a second fan blows outside air over the condenser. A large house or building may have several such units, allowing each room to be cooled separately.
In , General Electric introduced a popular portable in-window air conditioner designed for convenience and portability. Packaged terminal air conditioner PTAC systems are also known as wall-split air conditioning systems. PTACs, which are frequently used in hotels, have two separate units terminal packages , the evaporative unit on the interior and the condensing unit on the exterior, with an opening passing through the wall and connecting them.
This minimizes the interior system footprint and allows each room to be adjusted independently. PTAC systems may be adapted to provide heating in cold weather, either directly by using an electric strip, gas, or other heater, or by reversing the refrigerant flow to heat the interior and draw heat from the exterior air, converting the air conditioner into a heat pump.
While room air conditioning provides maximum flexibility, when used to cool many rooms at a time it is generally more expensive than central air conditioning. The first practical semi-portable air conditioning unit was invented by engineers at Chrysler Motors and offered for sale starting in Split-system air conditioners come in two forms: mini-split and central systems.
In both types, the inside-environment evaporative heat exchanger is separated by some distance from the outside-environment condensing unit heat exchanger. A mini-split system typically supplies air conditioned and heated air to a single or a few rooms of a building. Multi-zone systems typically offer a variety of indoor unit styles including wall-mounted, ceiling-mounted, ceiling recessed, and horizontal ducted.
Multi-zone systems provide extended cooling and heating capacity up to 60, Btu's. Large systems are known as VRF Variable refrigerant flow systems. Mini split ductless systems were invented by Daikin in , and VRF systems were also invented by Daikin in Advantages of the ductless system include smaller size and flexibility for zoning or heating and cooling individual rooms.
The inside wall space required is significantly reduced. Also, the compressor and heat exchanger can be located farther away from the inside space, rather than merely on the other side of the same unit as in a PTAC or window air conditioner. Flexible exterior hoses lead from the outside unit to the interior one s ; these are often enclosed with metal to look like common drainpipes from the roof.
In addition, ductless systems offer higher efficiency, reaching above 30 SEER. The primary disadvantage of ductless air conditioners is their cost. An additional possible disadvantage is that the cost of installing mini splits can be higher than some systems.