Air conditioning





An air conditioner (AC) is an appliance or mechanism designed to modify air
temperature, generally cooling it down. It was invented by Willis Haviland
Carrier (1876 - 1950) around 1902.

Air conditioning units may also reduce the humidity of the air processed by
the system. Since drier air aids evaporative cooling of people, this
improves the comfort provided.

From a mechanical engineering viewpoint, a modern air conditioner is a
specialized form of a heat engine. It is designed for maximum efficiency
when work is being applied to cool a living or storage volume by pumping
heat from a low temperature heat source to a higher temperature heat sink.
In electric units this is typically done by using an electric motor to drive
a compressor. The compressor compresses a working fluid. During compression
the working fluid is heated to a higher temperature than the higher
temperature heat sink. The working fluid is circulated to outside coils
where it cools to ambient air temperature. The working fluid is then
expanded (which lowers the temperature of the fluid via adiabatic cooling)
and circulated through an interior coil. The interior coil absorbs heat
energy from the interior air and transfers it to the working fluid which
then proceeds to the compressor to repeat the cycle.

In the past, "swamp cooling" was popular for improving comfort during hot
weather. It is a simpler system where air is blown over a moist mesh to cool
the air evaporatively, and it worked best in hot, dry climates.

Freon was commonly used as a working fluid due to its superior heat
conducting and capacitance properties. Unfortunately, it has become very
controversial as evidence has accumulated that it reachs the upper
atmosphere when it escapes. The chemistry is poorly understood but consensus
seems to have been growing that fluorocarbons act as a catalyst in the
presence of ultraviolet radiation and may be doing severe damage to the
ozone layer.

Air conditioner size is often measured in "tons". A "ton" is the ability to
remove 12,000 BTUs per hour. Residential central air conditioners can be 1-5
tons.

The sale of the appliance depends on seasons and weather. The sale usually
lifts a little or a lot in summer and particularly during heat waves.

The use of compressive AC is a major draw on electrical supplies in warm
climates where there are many units installed.