Figure 4-5.—Forced-air heating system.following paragraphs. For a discussion of heatingprinciples (including theory, measurement of heat, andheat transfer) and a discussion of the principles of refriger-ation and air conditioning, you should read chapters 9and 10 of Utilitiesman 3, NAVEDTRA 12532.HEATING SYSTEMThe purpose of designing and installing a heatingsystem in a building is to provide proper heatdistribution to the various rooms or zones within thebuilding. This can be done by means of various types ofheating systems.Warm-Air Furnace SystemsA warm-air furnace can be any type of heatingdevice that circulates warmed air to locations where itis needed. One type, the wall heater, draws in cold airnear the floor, passes the air over a heating unit, and thenexhausts the warmed air to heat the surrounding areaAnother type is the gravity warm-air furnace. It is adirect-fired furnace that transfers heat by convection Inother words, warmed air circulating through the furnacerises through ductwork to the areas to be heated andthen, as the air cools, it descends to the furmace to bereheated Since the installation of this type of systemrequires abasement and large, unsightly ductwork, it isseldom used in new construction.A more commonly used type of warm-air furnace isthe forced-air furnace (fig. 4-5). In this type, an oil orgas burner heats the fins of a heat exchanger. The heatexchanger warms the cool air passing over it. Thewarmed air is then forced, by fan, through relatively4-5
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