08-11-2012, 12:59 PM
PRINCIPLES OF AIR CONDITIONING
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BASIC CONCEPTS
Central air conditioning is considered a luxury rather than an essential in most parts
of North America. Air conditioning systems are more common in the southern areas
and are more common in humid areas than in dry areas. There are probably more
air conditioners per capita in Florida than in California, for example. You probably
have a good sense already as to how common central air conditioning systems are
in your area.
THE MECHANICS
The most common type of air conditioning that we see is technically referred to as
direct expansion, mechanical, vapor-compression refrigeration system.
The goal with air conditioning is to capture heat in the house and throw it outside
(Figure 1.1). But how can we take heat from a space that is already cooler than outdoors
and dump it into the outdoor air? One of the ways we can think about it is to
look at a refrigerator. If we can keep the temperature inside your refrigerator at about
40°F and it is 70°F in the kitchen, somehow we are taking heat out of that cool air
and dumping it into a kitchen that is warmer. Central air conditioning and refrigerators
operate on exactly the same principle. The process works something like this.
Review
Indoors To recap, we can think about a cold, low-pressure liquid entering an evaporator coil.
The warm house air gets blown across the cool coil by the furnace fan. The house
air gives up its heat to the cold liquid, boiling the liquid off into a relatively cool
gas. The cooled air that passed over the coil is distributed through the house.
Outdoors The cool gas in the pipe moves outside and is squeezed by the compressor into
a high-temperature, high-pressure gas. This hot gas passes through the condenser
coil. Blowing outside air across the condenser cools the hot gas inside, releasing heat
to the outdoor air that has been stolen from the house. As the gas is cooled, it condenses
back to a liquid.