Document jOm9KejOKxpx4Epx96rbK53p

404 CHAPTER 21 1948: Guide Table 8. Return Air--CarryingCapacity--Btu Serviced ! Return Air Com bination No..-. . Duct Dia In. 31 32 .. 33 34 35 36 37 38 10 12 .. 14 16 18 ,20. 22 24 .Type, A Btu per Hr Types B and C Btu per Hr . Type D . Btu per Hr . Type E Btu-per Hr 11,300 16,300 ; 9,500 .7,800 : 5,000 13,700 . 11,300 7,200 22,200 29,000 18,700. 15,300 24,400 i 20,000 9,800 12,800 36,700 : : 30,800 45,300 38,000 .25,300 31,300 16,200 20,000 54,800 ' 65,200 46,000 54,800 ' 37,800 24,100 .45,000... 28,700 . Type F Btu per Hr, ' Return Ant Com bination .. No- 7,800 11,300 15,300 20,000 25,300 31,300 37,800 45,000 . 31 32 33 34 35 36 37 38 The selected types of return air ducts and fittings are shown in Fig. a. Up to 20' Type B Same as Type E except_ that col lar and shoe are sne as for Type A. Type 0 . .Type E - ` Typ* F ''''"Note:- ForTypes C, D, E, and F retuni-air duct systems, reduce the carrying capacity shown in Table 8 . by 1 per cent for each 4.ft additional length in the horuontal ran. .. . Fig. 5: Typical Arrangements of Return^Air Duct Systems Design Procedure i!: The.steps to be taken in designing a gravity warm air duct system are: . 1. Calculate the heat loss from each room as explained in Chapters 6, 8 and 14. 2. Prepare: a layout.showing'(a) furnace, (ft) chimney connection, (c) warm air registers (whether floor, baseboard or wall),-(d) return air grilles. : 3. Indicate on each.warm air run (using symbols shown in Fig. 6): (a) whether the ; foom to be heated is on the:firstror second story, (ft) the approximate length of leader pipe in the basement, (c) the number of right angle elbows required, including the elbow at the boot connection (see Fig. 2), (d) whether the register is to be located in the floor, in the baseboard, or in the wall.................. 4. Show the number and proposed locations of return air grilles, and the. type of return air system (see Fig. 5). ...... Gravity Warm Air Systems 405 5. From Table 6, for first story, or from Table 7 for second story, select the combi nation number for the warm air system which will supply the heat required to each'room, with the number of elbows and length of leader pipe'previously determined. Then, using the combination number as found, read directly in Tables 1, 2, or 3 the leader, stack, and register sizes required. . 6. From Table 8 select the combinatidn number for the return air system to coiTespond with the Btu serviced and the type of return air system. Then from Table 4 select the duct and grille sizes, etc., corresponding to the same combination number:............. ........ 7. Select.a furnace having a register delivery, in-Btu per hour, equal t.o the total heat loss from'the structure. Design Examples ' ' Examples 1 and 2 will illustrate the use of the tables in selecting warm air and return system sizes. Example 1. For a room which has a heat loss of 22,500 Btu perhour select the size of first story warm air system. ' There are three elbows and the leader is approximately 10 ft long. (/Solution: Since,22,500 Btu is.beyond the capacities shown in Table 6, it is necessary to select two units of 11,250 each. From Table 6 in 10 ft leader column and in-section for three elbows find 11,400 as nearest capacity which corresponds to Combination Num ber 4 in first column. Refer to Combination Number 4 in Table 1 and find that the leader should beT2 in. in diame- ' ? ter and should be used with a , 12 x 14 in. floor register or a 13 x 11 in. baseboard register with a in.a. v umcatcd t j VACC 5K incextension.. . -! JL9.' I. INSULATCq | RCC, BOX' Example 2. VVhat ^'the size, of a return system, of Type D which'is'to service' 35,000 Btu perhour? - : --f Solution: From Table 8 find; Combination Number 37 which will service 37,800 Btu..per hour. Refer to Table 4 to find that ' Combination . Number 37 will require ^`22-inj; diameter duct, a shoe area of 420 sq in., a metal grille 18 x 30 in., a duct 42 x 10 in. or 36 x 12 in. If joist- lining is used the minimum depth ^hould,be l5 in. for two 2-joist, spaces 14 in. wide, or 10 in. for three joist spaces, , .... Fig. 6. Typical BXsement Line DraWii^G'' -REFERENCES , ,' *--The engineering data were obtained from University of Illinois, Engineering Experiment-Station Bulletins Nos. 141 188 189 and:246; Warm Air-Furnaces,and Heating.Systems, by A".C. Willard. A-PKratz^ V. S. Day, ahd .S. Konzo. See also Gravity Code, and Manual for Gravity Warm 'Air' Heating Systems, published by the i$atiornal''Wwnn.Air Heatingand `Air ConditiopingAssociationi: .x.'.l - '*--Simplified Procedure forSelecting Capacities of Duct'Systems for Gravity Warro^Air Heating Plants, by A. P. Kratz and S. Konzo {University of Illinois, .Engineering. Experiment Station Circular 45,: Dec,, 1942). ;* .................... ^ j" \ ' - v', ' . r*--Gravity Code and Manual for Gravity.Warm Air Heating Systems, Second Edition, i945 National Warm Air Heating and Air Conditioning Association, \