Document GXmKk5GXajo895N949dJoxvq

CHAPTER 20 . 1954 Guide, 16iz4e in the case of rectangular ducts. Warm air duets passing through cold paces or located in exposed walls, should have 1 to 2 in. of insulation. :'Special attention should be given to the problem of noise elimination. The metal duct connection to and from the furnace casing and fan housing should be broken by strips of canvas. Motors and mountings must be iarefully selected for quiet operation. Electrical conduit and water piping must not be fastened to, nor make contact with the fan housing. Instal lation of a fan directly under a return air grille is usually avoided. STANDARD COMBINATIONS OF PARTS ' The combinations of parts selected as standard by the National Warn Air Heating and Air Conditioning Association are shown in Tables 1 and 2. A method for selecting these combinations is indicated in the following section Simplified Method of Design. f SlOt WALL [ L"_______________ .._________ 3. 3. Recommended Type of Floor or Low Sidewall Installation on Out side Wall" ,: ' c Registers set to direct air upward along the w.al.l at.as.wide an angle as poss,ible. SIMPLIFIED METHOD OF DESIGN n A simplified method for selecting the combinations of branches, boots, and registers, is given3 in Manual 7 of the National Warm, AN ------ 1 iir Conditioning Association. In this method, the.sizes oft?6 CamKiicSnhjg. dSauUneiudtsAioai^rreiuCkowbo.tn.ad,initieodnwfinrogmAstwsooctiatb'iol'ens, g--im-v=in-~Wg+JtvIhO,oelu;iror nRB.tvt,u-i] canpacities.; , l ,lr' >per combination of parts for each branch can be determined if the follow- ; information is available. i information is avauauic. a. Location of room, that is, whether on first or second story. b. Actual horizontal length of duct from bonnet to boot, in feet. ,.-" cd.. BEtquuliovsaslefnrot mlenrgotohms itnofbeeethoefataeldl .fittings and of the register. Fig. 4 shows t Jues of equivalent lengths of fittings commonly used for domestic systems-' Forced Warm Air Systems 465 This simplified method is applicable to structures having heat losses not in excess of approximately 120,000 Btu per hour. The capacities shown in Tables 3 aiid 4 are based upon the most reliable data pertaining to fric tion losses and temperature drops in ducts.. They are also based upon a TOO deg temperature rise of the air, and a static pressure available for overcoming friction losses in the external duct system alone of 0.20 in. water gage. The use of this method assumes that the fan in the fanfurnace assembly will be capable not only of overcoming the resistance of the external duct system alone, but also the resistances imposed by the blower inlet, the filter, and the furnace casing. The combination numbers shown in the right hand column of Tables 3 and 4 correspond to those given Table 1. Warm Air Duct System Combinations of Parts Selected as Standard Combina tion No. >- Branch Pipe, Size In. Register Size, In. (See Figs. 1, 2, 3 and 4) Stack Size, In. Round Rec tangular Base-board High or Low Sidewall 2 34 5 Floor Registers* PERIMETER t_ 6 REPLACE MENT 7 Required Increase in .Width op Trunk Duct, In. 8 ` 41 10x334 5 3x8 10 x 6 4 x 12 8 x 10* i 42 10 X 334 6 4x8 10 x 6 4 x 12 8 x 10* 2 43 12 X 334 7 5x8 12 x 6 4 x 14 9 x 12* 3 44 14 x 334 8 6x8 14 x 6 6 x 14 9 x 12* 4 or longer 45 10 x 3M 9 8x8 (2) 10 x 6 (2) 4 x 12 10 x 12* 5 (2-Stacks) or (1) 24 x 6 46 12 x 3J4 10 10 x 8 (2) 12 x 6 (2) 4 x 14 12 x 14* 7 (2-Stacks) or (1) 30 x 6 Use these items only when the installation necessitates the use of existing floor openings. The sizes luted for floor registers correspond to the standard sixes for gravity warm air furnace systems, except for the ***& of the floor box collars. The use of standard blind boxes is suggested. A 12 x 51 in. stack may be on Combination 45, and a 14 x 51 in. stack on Combination 46 with floor registers. in Tables 1 and 2. Tables 3 and 4'are also applicable for the selection of the return air branches. A depth of 8 in. has been adopted as the standard for the trunk ducts. The width of a trunk duct serving two branches is determined by adding to the width of the remote branch the value shown in column 8 of Table 1, or column 8 of Table 2. DESIGN PROCEDURE FOR LARGE SYSTEMS4 For buildings having a heat loss in excess of 120,000 Btu per hour, the design procedure5 given in Manual 9 of the NWAll & ACA, may be used. Wrk sheets 9a, 9b, and 9c are available to simplify calculations.4 The Procedure consists of: L Calculation of design heat losses from individual spaces in the structure. The filiation of these losses 18 explained in Chapter 12.