Document e5oED4g4qVNOK4Mqya3MJDY9

American Society of Heating and Ventilating Engineers Guide, 1930 called stacks. The heated air is finally discharged into the rooms through registers which are set in register boxes placed either in the floor or in the side wall, usually at or near the baseboard. The air supply to the furnace may be taken (1) entirely from inside the building through one or more recirculating ducts; (2) entirely from Fig. 1. Value of Square Inch of Leader Pipe Area for First, Second, and- Third Floors outside the building, in which case no air is recirculated, or (3) through a combination of the inside and the outside air supply systems. Furnace heating plants may be: (1) of the gravity circulating type in which the motive-head-producing' flow depends upon the difference in weight between the heated air leaving the casing and pipes and the cooler air entering the bottom of the casing, or (2) of the fan circulating type in which a fan may supply all or part of the motive-head producing flbw. In most house installations, the former type of system is in general use. EIGHT DESIGN RULES The design of a furnace heating system involves the determination of the following items: 128 , Chapter 5--Heating with Warm Air Furnaces by Gravity a. Heat loss in B.t.u. from each room in the buildirtg. b. Area and diameter in inches of warm-air pipes in basement (known as leaders). c. Area and dimensions in inches of vertical pipes (known as wall stacks). d. Free and gross area and dimensions in inches of warm-air registers. e. Area and dimensions of (1) recirculating or (2) outside air supply ducts in inches. There may be one or more of each of these. f. Free and gross area and dimensions in inches of recirculating registers. g. Size of furnace necessary to supply the warm air required to overcome the heat loss from the building. This "size" should include square inches of leader pipe area which furnace must supply. It is also desirable to call for a minimum bottom fire-pot diameter in inches, which is the nominal grate diameter. h. Area and dimensions in inches of chimney lining and smoke pipe. If an unlined chimney is to be used, that fact should be made clear. CALCULATING HEAT LOSSES The heat which will be required for each room in the building depends on (1) the heat transmission losses through walls and glass as well as through floors and ceilings when the latter two are next to unheated spaces, and (2) the infiltration of cold air through the cracks around outside windows and <?oors. Calculations for the heat required in B.t.u. per hour should be made as indicated in Chapter 2, Heat Losses from Buildings. LEADER PIPE SIZES In a gravity circulating warm-air furnace system the size of the leader to a given room depends on the temperature of the warm air entering the room at the register. A reasonable air temperature at the registers must, therefore, be agreed upon before the system can be designed. The National Warm Air Heating Association has approved an air temperature of 175 deg. fahr. at the registers as satisfactory. At this temperature, the heat-carrying capacity (heat available above 70 deg. fahr.) per square inch of leader pipe per hour for first, second or third floors is shown by Fig. l at 175 deg. fahr. to be 105, 170 and 208 B.t.u. respectively. For average calculations, the values 111, 166 and 200 will simplify the work and may be satisfactorily substituted for these heat-carrying capacities. If H represents the total heat to be supplied any room, the resulting equations are: Leader areas for first floor, square inches = = approximately 0.0091? (1) H Leader areas for second floor, square inches = jgg = approximately 0.006H (2) Leader areas for third floor, square inches = = approximately 0.005ff "(3) In designing for a lower warm-air register temperature, say 160 deg. fahr., the factors 111,. 166 and 200 become 80, 140 and 166 (Fig. 1 at 160 deg. fahr.), and the resulting equations are: 129