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American Society of Heating and Ventilating Engineers Guide, 1936 with a constant register or delivery temperature maintained, provided that the rate of fuel consumption can be increased to provide the necessary heat. In other words, the capacity of a forced circulation system is limited by the ability of the chimney to produce a sufficient draft. Table 1. Summary of Data Applied to Warm Air Research Residence . Rooms From Chapter 7 Estimating Heat Losses Btu Heat Losses H Leader Area Sq In. Stack Area Leader . Sq In. .. Diameter 0.7 X LA Inches Stack Size Net ' Register Size Gross First Floor = 0.00977 Living--:-----Dining. . Breakfast___ Kitchen. 17250 6810 2300 9210 155 61 21 83 ___ 14 -- 9 _ _ 8 _______ 11 or 12 ________ 14 X 16 8 X 12 8 X 10 12 X 14 Sun.. __ 25710 Hall and stair 12570 230 113 .... Two 12 Two 12 X 14 _ 12 ________ 12 X 14 Second Floor = 0.00677 Owner's 15030 90 63 11 or 12 5 X 12 S'. W. Bed. 9800 59 41 9 3HX 12 Bath,,......... 2450 15 10 8 3 X 10 N. Bed._____ 14800 89 62 11 or 12 5 X 12 12 X 14 8 X 12 8 X 10 12 X 14 Third Floor E. Bed. _ .. W. Bed_____ 8220 8220 = 0.00577 41 41- 29 29 8 3 X 10 8 3 X 10 8.X 10 8 X 10 ________ BOOSTER FANS ' Booster fans often may be arranged to operate when gas or oil burners are running and to stop automatically when the burners shut down. The booster equipment is most effective in increasing output at low operating temperatures. According to tests, efficiencies may be advanced from 60 per cent for gravity to 70 per cent with boosters at low operating tem peratures, but at high operating temperatures gravity and booster efficiencies are almost identical?: . See University.of Illinois Eng. Exp. Sta.. Bulletin No. 141, p. 79. ' PROBLEMS IN PRACTICE 1 What may prohibit the use of a gravity warm .air system in a large house having several exposed wings? . Inagravity'warmair' system, excessive.vertical distances above the furnace cause.little trouble iri the design of the Wall stacks, but excessive horizontal distances from the furnace should be carefully considered in the design of the leaders. To work effectively, a gravity warm air system should be balanced and leaders over 12 ft in length should be avoided if possible.' Long leaders', if used, must be of ample size, well pitched, and well iiisulated. Large houses having-exposed wings may require leaders much longer than 12 ft-; infiltration may createsevere back-drafts in the exposed wings; and the basement ceiling height may not be sufficient to allow the leaders to have a pitch of more than one inch per foot. These conditions may make the exposed wings very difficult to heat with a gravity system because of its low air head differentials. 430 Chapter 24--Gravity Warm Air Furnace Systems 2 A third-story bedroom has a calculated heat loss of 12,000 Iftu pec. hour. a. What size leader pipe should be used for a 175 F register air temperature? b. What size stack? c. What size register? 12 000 a. Leader area = = 60 sq in. Use leader with diameter of 9 in. b. Stack area = 0.7 X 60 = 42 sq in. Use stack 3J^ in. by 12 in. - c. Register gross area - jjy = 85.7 sq in. Use register 8 in. by 12 in. 3 The calculated heat loss of a house is 130,000 Btu per hour. Find the grate area required for the furnace under the following conditions: Heating value of coal = 12,500 Btu per lb. Furnace efficiency = 55 per cent. Combustion rate = 7.5 lb per sq ft per hour. Ratio of heating surface to grate area of furnace Register temperature -- 175 F. Loss between furnace and registers = 20 per cent. Grate area = 01..620XX14142,5X00--13X0,070.50- = 399.5. sq .in. Grate diameter = 22.6 in. Use grate with diameter of 23 in. 20 to 1. 4 If in Question 3 the conditions were the same except that the ratio of heating surface to grate area of furnace was 24 to 1, what size grate would be required for the furnace? Grate area = 1.2 X 144 X 130,000 0.60 X 12,500 X 7.5 X Grate'diameter = 21.7 sq in. Select grate with diameter of 22 in. 1 1 + 0.02 (24 - 20) _ 399.5 1.08 370 sq in. 5 Name the items involved in the design of a furnace heating system. a. Heat loss from each room, Btu. b. Area and dimensions of warm-air pipes in basement, inches. c. Area and dimensions of vertical pipes, inches. d. Free and gross area and dimensions of warm-air registers, inches. e. Area and dimensions of recirculating or outside air ducts, inches. /. Free and gross area and dimensions of recirculating registers, inches. g. Size of furnace necessary to supply the warm air to overcome.the heat loss: h. Area and dimension of chimney and smoke pipe, inches. 6 Discuss the design features of. recirculating ducts. , a. Their area should be equal to or greater than that of the supply ducts. b. They should be streamlined, and have a minimum number of turns. c. All runs should be as short as possible.' d. Account should be taken of all cold walls and window areas in determining sizes and positions of return air inlets. e. The return line should be pitched downward toward the furnace. It . should be designed to minimize friction. /. The top of the shoe or boot should never be above the grate level. 431 X