Document 2a6LEwkoRpoGQmBvjdQyKyG7

480 CHAPTER 20 1956 Guide 'Ok- Table 2. Capacity and Sizing Table--Second Story For Warm Air and Return Air Stack, Branch, and'Registers Equiy. Length or Fittings and Registers Horizontal Length Furnace to Register ] naulated Ducts* Attic Ducts CoL a Col. b Col. c. Col. d Ud to 70 Eq. Ft. ----------------- 71 to 100 Eq. Ft. Up to 7 8-12 13-17 18-25 26-35 36-45 46-55 Up to 7 6-12 13-17 18-25 26-35 36-45 46-55 Up to 5 6-9 10-13 14--IS 16-25 26-35 36-45 46-55 Up to 5 6-9 10-13 14-18 19-25 26-35 36-45 46-55 101 to 130 Eq. Ft. Up to 7 6-12 13-17 18-25 Up to 5 6-9 10-13 14-18 26-35 36-45 46-65 19-25 26-35 36-45 .46-65 131 to 165 Eq. Ft. Up to 7 8-12 13-17 18-25 26-35 36-45 46-55 Up to 5 6-9 10-13 14-18 19-25 26-35 36-45 46-55 166 to 200 Eq. Ft. Up to 7 8-12 13-17 . 18-25 26-35 36-45 46-55 Up to 5 6-9 10-13 14-18 19-25 26-35 36-45 46-55 6,300 5,700 5,200 4,800 4,100 3,500 3,100 2,800 5,000 4,600 4,300 4,000 3,400 3,000 2,700 2,300 4,200 3,900 3,700 3.500 3,000 2,600 2,400 2,000 3,800 3,500 3,200 3.000 2,700 2,300 1,900 1,800 3,500 3.200 2.900 2.700 2,500 2,100 1,900 1,500 Combination Number Size Rectangular Branch Size Round Branch Size (Diam) Number of Joist Spaces and Minimum Depth-Return Air Rogi>frg; Low Wall. High Wall or Baseboard: Registers: Floor, Warm Air- 41 1 10x3% Second Story Room Heat-Loss--btuh Registers: Floor, Return Air 6x10 Trunk Duct Increase, Inches * Uninsulated ducts in heated spaces and insulated ducts in unheated spaces. b Note: For return air a 14x3% in. stud space may be used instead of 10x3% in. stack'. Where 12x3% in. or 14x3% in. stack is required, a 14x3% in. stud space may be used only when inside of stud space is smooth and without protruding plaster keys. The number of joist spaces for combination 47 is'based on 2x8 joists. One space may be used with 2x10 joists. The limiting factor for a duct combination is the stack capacity. Forced Warm Air Systems 481 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 1 and 2 are based upon the most reliable data pertaining to fric tion 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. Tables 1 and 2 are applicable for the selection of both warm air and return air branches. A depth of 8 in. has been adopted as the standard for trunk ducts, and where a branch joins the trunk the required increase shown in the last line of Table 1 or Table 2 refers to an 8-in. trunk duct. Where two branches form a trunk the farthest branch is considered to be the trunk and its equivalent width (for 8-in. depth) is increased as required. DESIGN PROCEDURE FOR LARGE SYSTEMS4 For buildings having a heat loss in excess of 120,000 Btu per hour, the design procedure6 given in Manual 9 of the NWAH & ACA, may be used. Work sheets 9a, 9b, and 9c are available to simplify calculations.4 The procedure consists of: 1. Calculation of design heat losses from individual spaces in the structure. The calculation of these losses is explained in Chapter 12. 2. Location of registers and return intakes on floor plan, showing types of registers, with distance from register to opposite wall and deflection of registers desired. 3. Laying out a proposed duct system for both warm air and return air sides of the system, and including details of types of fittings and the actual and equivalent lengths of each branch line from bonnet to register, without sizes. (See Fig. 4, Groups 1 through 6, for equivalent length of fittings.) 4. Determination of bonnet temperature. If the rating sheet for a furnace-blower unit specifies a fixed value of bonnet tem perature, locate this temperature in the left-hand column of Table 3. If not speci fied, use the following procedure: Use Table 3 for buildings having a heat loss between 120,000 and 350,000 Btu per hr, or Table 4 for buildings having a heat loss greater than 350,000 Btu per hr. Select shortest actual length, including vertical risers and read downward in nearest column in Tables 3 or 4 until lower heavy diagonal line is reached, but do not cross line. Run horizontally to first column of table and note bonnet temperature. Also select longest actual length including vertical risers, and read downward in nearest column in Tables 3 or 4 until upper heavy diagonal line is just crossed. Run horizontally to left to obtain value for bonnet temperature in first column. Select as the design bonnet temperature any value between these two limits. 5. Determination of air volume to be delivered through each register and the respective register air temperatures. Using Tables 3 or 4 and the design bonnet temperature selected, find the values of cfm per 1000 Btu for each duct length, and the corresponding register temperature. 6. Selection of register sizes and pressure losses to produce necessary throw, for the air volumes handled. Use Tables 5 or 6 to obtain required free area and pressure loss of register.