work on basically the same principle as kitchen
refrigerators, only without the insulated outer shell.
Contrary to popular perception,
conditioning is not
about adding cool air
to the room, but more about drawing heat away from it. The
end result is a space with significantly less heat, which
makes it feel cooler to occupants.
advantage of the effects of evaporation, much like a swab of
alcohol makes a person's skin feel cooler as the liquid
evaporates. The alcohol doesn't lower the person's skin
temperature, but rather draws away heat from the
air as it turns to
contain a special chemical called a refrigerant,
which has the unique ability to change from a gas to a
liquid in a short amount of time. A refrigerant called
freon is commonly used in
although there are other commercial refrigerants available.
The refrigerant is pumped into the
at the factory, along with a small amount of lubricating oil
for the compressor.
The parts of a
form a closed system consisting of a compressor, a
condenser, an expansion valve and a thermostat. Motorized
fans move the conditioned
air, while thin metal fins allow heat to dissipate
quickly, from or too the tubes containing the refrigerant
with the refrigerant entering the compressor, usually
located at the bottom of the external unit. At this point,
the refrigerant is a cool gas. As the gas enters the
compressor's inner chamber, the compressor squeezes the
refrigerant and the gas becomes a very hot liquid under high
pressure. This hot liquid goes through a series of
condensing coils placed outside of the room being cooled.
The heat dissipates into the outside
air, much like a
car's radiator dissipates heat from the engine coolant. Once
the refrigerant reaches the end of these coils, it is
significantly cooler and in liquid form.
This liquid is
still under high pressure, like the contents of an aerosol
can. In the case of air
liquid refrigerant is forced through a very tiny opening
called an expansion valve. This would be the same as the
sprayer on the aerosol can. The liquid refrigerant comes out
of the other end of the expansion as a very fine mist.
Because the refrigerant evaporates at a much lower
temperature than water, it begins to evaporate while
traveling through another set of coils. It is this
evaporation action that draws heat out of the surrounding
air, including the
air contained in
the room. The air
fan blows across metal fins placed over these coils, causing
the effect of cooling in the room.
At this point, the
liquid refrigerant becomes a cold gas again and re-enters
the compressor, where the entire process begins again until
a thermostat registers a specific temperature and shuts off
the compressor. When the room warms up, the thermostat
senses the added heat and the compressor kicks back on to
create more of the hot pressurized gas. At some point, the
temperature of the room may equal the cooling power of the
air conditioner and
the compressor will shut off again. The
systems of most houses do benefit from energy-saving steps
such as using window shades and keeping doors closed, since
they don't have to work as hard to keep the room at an
acceptable level of cool.
valve to change over to heat pump mode
condenser unit with compressor
Interconnecting refrigerant pipe