Document ppO9RpygE146M0bvQekR5GBzw

410 CHAPTER 22 1948: Guide Mechanical Warm Air Systems 411 GROUP Branch Angles and Elbows (not including boots) This simplified method is applicable to structures having heat losses not in excess of approximately 150,000 Btu per hour. The capacities shown in Tables 3 and 4 are based upon the most reliable data pertaining to friction losses and temperature drops in ducts. They are also based upon a 100 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.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 Duct below joist- 30 {includes Return Intake) Qnc/udes Return^ Intake) Group 7. Registers (Inducting losses in stacthead and velocity pressure) TABLE 7. Equivalent Length for Registers. (See diagrams at right) Deflec Baseboard High Sidewall 'Register tion or Low For throw of air of Angle Sidewall less than over d. &qister 13 feet 13 feet O' 35 Eg. Ft 35 Eg. Ft. 10 Eg. Ft. 40 40!5 - - - SO - 22 45 ' 45 40- - 30' 60 - - 60 - - us - - 45" H5 U5 ' \ 230- Notes for Table 7. a) When turning' vanes are used m stack- head use 0.7 of values tn columns Zto4. h) Values shown in 2nd and 3rd columns in Table are for &in. height registers (Standard height), and those in 4th column are for 4in height registers. For 5in. height registers, multiply, values in Co! 2 and 3 by !3 For 0in. height registers, multiply values in Col. 2 and 3 by 0.8_____ For 2-way deflection registers, add the vertical arid horizontal deflection angles . together and multiply by 0.7. Select-, closest angle "a" in Col. I of Table 7 .Fig. 3. Equivalent Length of Fittings (Continued) 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 9 of Table 1, or column 8 of Table 2. AUTOMATIC CONTROLS Air stratification, high bonnet temperatures, excessive flue gas tem peratures, and heat overrun or lag in a properly designed system can be largely eliminated through proper care in the planning and installation of the control system 3; desirable controls usually employed are: 1. A thermostat located in a living room where maximum fluctuation in temperature can be expected, in order to secure frequent operation of fans, drafts, and ;bumers. The thermostat location should not be on an outside wall, in a bed room, bath room or