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Heating Ventilating Air Conditioning Guide 1938 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 Sire Net Register Sire Gross First Floor Dining.--------Breakfast___ Kitchen. Sun__ Hall and stair Second Moor Owner's ___ S. W. BedBath .. _ N. Bed_____ Third Floor E. Bed. W. Bed_____ 6810 2300 9210 25710 12570 15030 9800 2450 14800 8220 8220 = 0.009H 155 61 21 83 230 113 = 0.00677 90 59 15 89 = 0.00577 41 41 __ ,, , . _ _ 63 41 10 62 29 29 14 9 8 11 or 12 Two 12 12 ......... ______ 14 X 16 8 X 12 8 X 10 12 X 14 Two 12 X 14 12 X 14 11 or 12 5 X 12 9 3H X 12 8 3 X 10 11 or 12 5 X 12 12 X 14 8 X 12 8 X 10 12 X 14 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 identical9. University of Illinois, Engineering Experiment Station Bulletin No. 141, p. 79, and No. 246. PROBLEMS m PRACTICE 1 What may prohibit the use of a gravity warm air system in a large house having several exposed wings? In a gravity warm air system, excessive vertical distances above the furnace cause little trouble in 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 insulated. Large houses having exposed wings may require leaders much longer than 12 ft; infiltration may create severe 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. 2 # A first story dining room has a calculated heat loss of 12,000 Btu per hour. a. What size leader pipe should be used for 175 F register air temperature?' b. What size register? 390 (V t I Chapter 19. Gravity Warm Air Furnace Systems a. Leader area = 12 000 = 108.1 sq in. Use leader with diameter of 12 in. b. Register gross area = 108 = 154 sq in. Use 12 in. by 14 in. register. 3 # A third-story bedroom has a calculated heat loss of 12,000 Btu per 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 in. by 12 in. c. Register gross area = j^y = 85.7 sq in. Use register 8 in. by 12 in. 4 0 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 = 12,790 Btu per pound. Furnace efficiency = 55 per cent. Combustion rate = 7.5 lb per sq ft per hr. Ratio of heating surface to grate area of furnace = 20 to 1. Register temperature = 175 F. Loss between furnace and registers = 25 per cent. See Equations 9 and 10: Grate area = 0.004205 X 130,000 = 547 sq in. Grate diameter = 26.3 in. Use grate with diameter of 26 in. 5 If in Question 4 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 = 0.004205 X 130,000 1 + 0.02 (24-20) Grate diameter = 25.4 in. Select grate with-diameter of 25 in. 547 1.08 = 506 sq in. 6 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. 7 Discuss the design features of recirculating ducts. . Their area should be equal to or greater than that of the supply ducts. . 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. 391 X