How Air Conditioners Work
Although the term “Air Conditioning” applies to any means of regulating or
changing the temperature, humidity, or disinfecting the indoor air for either
mechanical processes or human comfort, this article refers to the air
conditioning units used to dehumidify and cool the air.
Air conditioners are units or machines that cool the air by extracting heat from
an area. This is usually accomplished by means a refrigeration cycle which
forces heat from an area (such as the interior of a refrigerator or a warm room)
into an even warmer heat sink (the kitchen or the exterior of a home). The coils
of an air conditioner collect the heat from the giving source and transfer it to
the heat sink, thus cooling the internal area. This is usually achieved with the
use of a refrigerant, or cooling liquid that evaporates as it collects heat and
releases the heat into a separate area as it cools. The liquid is then recycled
back into the coils of the warm room to repeat the process.
Air conditioners also decrease the humidity of a room via the processes of
condensation. As the air inside a room cools, water vapor condenses on the
cooling coils and the units usually transfer this water to either a collection
device or deposit it directly outdoors as they deposit the heat from the coils.
Dehumidifiers work in the same way by condensing water vapor and transferring it
to a collection device or drainage tube, but a heat exchanger is used to keep
the temperature of the room consistent.
Refrigerants and cooling liquids are needed for most air conditioners and the
most common of all is Freon, a chemical produced by Dupont and other companies.
In recent years this gas, a chlorofluorocarbon, has been linked to the breakdown
of the ozone layer due to the chemical reactions of its chlorine atom in the
atmosphere. Over the next few decades, Freon will be phased out of the market
and other coolants will replace it as a common refrigerant. These other coolants
fall into the category of hydrofluorocarbons and contain no chlorine atoms.
Many homes, hotels, and buildings use window or wall air conditioners to
cool an area. These units typically cool air inside the room and use the outside
air as both a heat sink for the air and drainage for condensation. These units
also allow air flow between the exterior of the building and the specified room
through the use of a fan. Because of the limitations of these air conditioners, however,
they cannot properly cool large areas. Buildings or homes typically use many of
these wall units to regulate overall temperature and air quality.
Evaporation coolers (otherwise known as swamp coolers or Persian coolers) are
simple units that use evaporation to cool a room. These are typically used in
hot dry climates where humidity is very low. Evaporation units pull outside air
through a moist surface like a sponge and transfer the resulting humidity to the
room. The warm energy of the inside air transfers to the water vapor and cools
the air.
Some larger facilities have absorptive coolers that run cold water through ducks
as a means of hydronic cooling. These coolers are run from gas turbines that
produce electricity as well as heat for commercial and industrial buildings.
Most facilities and homes, however, use central air conditioning to cool the
interior space. The air conditioners use a duct and vent system to move air throughout the
structure and back to the main air conditioning unit somewhere outside of the
building. With the help of filters in the vents, central air removes dust and
allergens from the air while it cools the space. These air conditioners are also
significantly quieter than traditional window units since they reside outside
the living areas.
Buildings equipped with HVAC systems (heating, ventilation, and air conditioners
combined into one system) typically use thermostats so that individuals can
properly control the temperature. Thermostats are usually set to either the
heating or the cooling unit. For example, if the thermostat is set to control
the heating elements of the system, it will not cool the building should it get
too hot. Despite this downfall, thermostats are the easiest means by which to
regulate HVAC systems.
Air Conditioners waste about 40% of the energy they use. This wasted energy is
the heat generated during use. During peak summer months, cities sometimes
require additional energy in order to meet demands due to air conditioner usage.
Due to this energy waste, some countries require residential air conditioners to
meet certain specified standards for energy efficiency. This rating, known as
the Seasonal Energy Efficiency Ratio (SEER), measures the cooling output (in
BTU) of the machine against the watt-hours (Wh) over the same period of time.
The higher the SEER rating, the more efficient the machine.
The calculation looks like: SEER = BTU/Wh
Most units in the United States have SEER measurements of 9 or higher and new
units are required to have a minimum SEER rating of 13. In most large buildings,
this improvement in energy efficiency results in lower energy bills.
The effectiveness of air conditioners can decrease with significant increases in
the temperature of the heat sink. For example, most air conditioners fail to
work as well when the outside air (heat sink) reaches 120 degrees. Under these
conditions, the air cannot absorb any more heat. Air conditioning units that use
the ground as a heat sink and source do not have this problem since the ground
temperature does not fluctuate as much throughout the year.
Home insulation also increases the effectiveness of air conditioners.