For summer air conditioning, the air conditioned space is maintained at a temperature lower than the surrounding temperature. The moisture content may also have to be maintained at a level lower than the atmospheric level. So there has to be transfer of heat as well as ingression of moisture from the surroundings to the air conditioned space. Further, we have to take into account the heat generated by occupants, electric lights, fans and other appliances.
The air-conditioning plant is designed to maintain the specific internal air temperature and humidity when the expected heat gain and losses occur. The cooling load on refrigerating equipment seldom results from any one single source of heat. Rather, it is the summation of the heat that usually evolves from several different sources. Some of the more common sources of heat that supply the load on refrigerating equipment are as follows :-
-heat that leaks into the refrigerated space from the outside by conduction through the insulated walls.
-heat that enters the space by direct radiation through glass or other transparent materials.
-heat that is brought into the space by warm outside air entering the space through open doors or through cracks around windows and doors.
-heat given off by warm product as its temperature is lowered to the desired level.
-heat given off by people occupying the refrigerated space.
-heat given off by any heat-producing equipment located inside the space, such as electric motors, lights, electronic equipment, steam tables and materials handling equipment.