Heating Systems 319
Figure 12-7. A simplified heat-pump circuit diagramAir Conditioning Systems
The increased use of air conditioning systems provides greater com-
fort in homes, industrial plants, and commercial facilities. Most air condi-
tioning units are used for the purpose of controlling the inside tempera-
ture of buildings, so as to make working and living conditions more com-
fortable. However, many units are used to cool the insides of various types
of equipment. Both air temperature and relative humidity are changed by
air conditioning units. In the design of air conditioning systems, all heat-
producing items in the immediate environment must be considered. Body
heat, electrical appliances, and lights represent some common sources of
heat. The diffusion of heat takes place through floors, walls, ceilings, and
the windows of buildings. A simplified diagram of a room air condition-
ing unit is shown in Figure 12-8.Considerations for Heating Loads
Heating systems used for residential, commercial, and industrial ap-
plications are usually referred to as HVAC systems. This means heating
ventilation and air conditioning system. The electrical power requirement
for HV AC systems is a major concern for electrical system design for a
building. Electrical HVAC systems provide individual thermostatic tem-
perature control, have long equipment life, and are safe to use. A well-
insulated building is necessary to reduce heat loss for economical use of
HVAC systems.