Document 0q83Bb2ONpJLVr3yD25XQ3onx

476 CHAPTER 20 1955 Guide ; CR0UP 7 registers (including losses in stackhead and velocity PRESSURE I i i} 4I i \ ' ^able 4A. Equivalent Length foh .Registers Deflection Angle A Baseboard,. High or Low . Sidewall Registers Floor Registers with Bor only 4r 25 15 22 30 40 45 60 45 115. Fig. 4. Equivalent Length of Fittings (Concluded) - I nmaurp is not high enough to accommodate the pressure loss " fhrhiifelJthe registers use a higher bonnet pressure. If the register pre- surrifcnUcanTirge^tma/be neiessary to ^uce itby either using . two registers in place of one, or using.smaller deflection angles. i" " b Obtain actual duct loss by subtracting total register pressure loss, as i ). . determined from Tables 5 or 6, from maximum bonnet pressure. ! r- c. Obtain the pressure drop, in each duct per 100 ft by use of Table . .#4 Determine duct size by means of air friction chart (sudh as Fig. 1, or Fig. , Chapter 32), volume (cfm), and pressure drop per 100 ft of duet. ; B. Return air branches. ^, a. Select a low value of actual duct loss obtained from step b under item a i for the suction loss of return duct system. ... .f r b. Proceed in sizing return air branches by the same method described for j - the warm air branches. ! j C. Tmrik ducts for 'warm air and return air sides of system a 'Add air volumes'of branches to be handled by each trunk duct. friction loss per 100 ft of trunk duct is determined by taking tne e mnallS of the two values for friction loss for the two ducts meeting at the junction. ,. ! c. Determine trunk duct size by using an air friction chart, volume (elm; ' and pressure drop per 100 ft of trunk duct. 8. Selection of Blower. , | A/-Determine total cfm air delivery (the sum of all branch cfm values;. ; B. Determinp. static pressure requirement. ' ' ' ,,KSure i # a...For furnace-blower combination units it is the sum of bonnet- pressure ' ' "and siiction pressure. ' .... , i.^nnct b. For blowers separately selected from the furnace it isi the: sumo wagh. pressure, suction pressure, filter loss, casing loss, losses through ers, coils, and other devices. 9. Selection of Furnace. A. Determine register delivery (the sum of room Btu losses). B Determine bonnet capacity. . , . n8Q Bonnet capacity = (total cfm) X (temperature rise) X 1-Q89. ^ C. Determine allowance for pick-up load. For buildings whichareheate ^ termittently, such as churches and auditonums, it is custom J turt. from 10 to 25 percent extra furnace capacity for warming of the 7'a u i.k 3. Se l e c t io n o r B o n n e t T e m p e r a t u r e , R e g is t e r T e m p e r a t u r e a n d R e g is t e r D e l iv e r y (CFM )** (For B u ild in g s H aving a Heat Loss between 120,000 and 850,000 B T U /H r .) Register D elivery Volum e-in C F M per WOO B T U per H r. 87 4 2 .7 90 3 8 .6 93 3 4 .0 97 3 0 .5 io b 2 8 .0 1 1 0. 22 1' 8:; cq s. T- 1- oeo~ t oo3 in co oCQ CQ <l8^< i< CO OOO 05 CO . 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