Invented by
Willis Haviland Carrier in 1902 (hence the famous
Carrier brand of AC machines),
air conditioning was a major factor in the massive increase of
population in
Texas,
Florida and the
Southwest, as well as other
tropical regions worldwide. The process of turning
air into a
temperature more comfortable for
human habitation makes
life all the better, decreases
frustration (it's been proven scientifically), and makes living in
hot areas much more appealing. Frankly, if it wasn't for
air conditioning, I would refuse to live in
Shanghai.
The central feature of an air conditioning system is the air conditioning plant. Fresh air, together with a proportion of the air returned from the air-conditioned rooms (recirculated air) is drawn into a mixing chamber, the relative quantities of fresh air and recirculated air being controlled by valves. This air is cleaned by means of filters. These usually have glass-wool filter elements in which dust is retained.
After filtering, the air is preheated. This is done by means of heating pipes through which steam or hot water is passed and which are provided with fins which serve to increase their heat-exchange surface area.The air to be preheated flows along these fins and absorbs heat from them. Excess moisture is removed from a portion of the air by cooling. The warmer the air is, the more water vapor it can absorb.
This air is then mixed with the air coming straight from the preheater so as to obtain an air mixture of the desired temperature. If the moisture content of the mixture is too low, finely atomised water is added by spray nozzles. This causes some cooling of the air, and for this reason the air is passed through a reheater which is essentially similar to the preheater and which gives the air its desired final temperature.