Document RJ5K86dkeN25y8pbX7DR11wyB

240 CHAPTER 18 1959 Guide is accessible. Splitter dampers for volume control are not niftommp.nHfirf, Return systems having more than one return intake may be equipped with balancing dampers. This is particularly desirable with systems in which the supply outlets are lo cated on the inside wall or in the ceiling of the conditioned rooms. 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 fire resistant fabric. Motors and mountings must be care fully selected for quiet operation. Electrical conduit and water piping must not be fastened to, nor make contact with the fan housing. Installation of a fan directly under a return air grille is usually avoided. SIMPLIFIED METHODS OF DESIGN Simplified methods of design have been developed for sev eral types of forced warm air beating systems. In general, the specific procedure chosen depends upon the type of system and the type of structure in which it is to be used. In most cases, more than one type of system may be used in a specific structure. It is therefore necessary to first choose the system desired and then determine the applicable design procedure. Perimeter-Loop Systems in Concrete Slab Con struction The perimeter-loop system,* shown in Fig. 4, conveys the warm air through embedded ducts to perimeter diffusers. The air is delivered from the furnace to feeder ducts which extend radially to the loop duct. The air flows through the loop duct to the diffusers. The ducts serve the dual purpose of conveying the warm air and of warming the floor. Al though the design of the concrete slab is not specifically the concern of the mechanical engineer, it is absolutely necessary that he understand the considerations involved lest im proper construction be used with consequent adverse effect on the performance of the hearing system. For information on slab construction, as well as duct placement, duct insula tion, etc., see Manual 4 of the National Warm Air Heating and Air Conditioning Association.* A' section of typically in stalled loop duct is shown in Fig. 5. Simplified design procedures are contained in Manual 4. One of these procedures subject to the following limitations: total heat los 100,000 Btub, maximum perimeter 210 ft, and maximum length of uninsulated feeder duct 30 ft for area served by one furnace; is the following: 1. Calculate the beat loss for each room using the methods explained in Chapter 12. For subfloor and edge losses* see Manual 3 of the National Warm Air Heating and Air Con ditioning Association. 2. Determine the required furnace-bonnet capacity from the heat Iosb of the building. 3. Locate the diffusers on the plan. For best heating results, if a room has a heat loss of more than 8,000 Btuh or if it has two or more exposed walls, use two or more diffusers. Propor tion the Btuh heat loss of each room among all diffusers in that room. 4. Locate, the feeder ducts. First, divide the heat loss of the structure by 15,000 to determine the probable number of feeders. Second, locate the ducts so that they connect with the perimeter-loop at areas of greatest heat loss or in rooms where warm floors are particularly desirable. Third, locate the feeder ducts so that no more than 3 diffusers are in the section of loop duct between any two feeders. (The final number of feeder ducts may be larger than that originally estimated.) 5. Determine the size of feeder ducts using Table 2. Assume that the Btuh required by each diffuser will be supplied by the feeder nearest it. uetermine the feeder duct diameter from its length and the total diffuser Btuh delivery carried by it. . 6. Determine the total diffuser free area required in each room ng Table 3. Measure the length of feeder duct under each room. Add to this one-half of the length of the loop duct, and determine the total diffuser free area required. Apportion this among all diffusers in the room. 7. The diameter of the loop duct should be uniform and equal to the diameter of the largest feeder duct. Perimeter-Radial Systems in Concrete Slab Con struction The perimeter-radial system, Fig. 6, is similar to the per imeter-loop system in that the supply ducts are embedded in the concrete slab. The feeder ducts of the radial system ex tend directly from the subfloor plenum to the perimeter dif fusers, and there is no loop duct around the perimeter of the floor. The feeders do provide floor-warming, but not to the same degree provided by the feeder and loop ducts of a perimeter-loop system. The same considerations of slab con struction and edge insulation apply to both systems. A simplified design procedure* using 6-in. diameter duct and subject to limitations of: 1,000 to 1,200 sq ft maximum area, not more than approximately 15 ft along perimeter between diffusers, and no radial duct substantially longer than 20 ft, is the following: 1. Calculate the heat loa of each room or area using the method explained in Chapter 12. For subfloor and edge losses, see* Manual 3 of the National Warm Air Heating and Air Conditioning Association. 2. Determine the required furnace-bonnet capacity from the heat loss of the building. 3. Locate the diffusers on the plan. Allow at least one dif fuser for each exposed wall in each room or area of the build ing and preferably beneath window areas. For residential in stallations, limit each diffuser to a maximum of 7,000 Btuh. This is a preliminary estimate of the number of diffusers needed. 4. Measure the length and count the number of elbows in eaeff feeder duct. Determine Btuh capacity of each feeder duct from Table 4. Use Table 4 (Section A) for side-wall and floor diffusers and Table 4 (Section B) for baseboard diffusers. 5. If the total Btuh capacity of ail feeders to each room or area equals or exceeds the heat loss of that room or area, the number of feeders initially chosen is satisfactory. If the heat loss exceeds the Btuh capacity of the feeders, use and locate additional diffusers and feeder ducts. 6. The cfm values in Table 4 are used for designing the return-duct system. Perimeter-Radial System in Crawl Space or Base* ment Construction The perimeter concept of warm air heating has been ap plied to crawl-space and basement homes by locating the diffusers in the perimeter location and by warming the area underneath the floor of such structures. Although the con struction of the crawl space and the foundation wall is the responsibility of the architect and the general contractor, it is important that the engineer cheek the construction to make certain that it will not adversely affect the perform ance of the heating system. Details on crawl-space con struction are shown in Manual 4 of the National Warm Air Heating and Air Conditioning Association* The crawl space or basement should be heated to provide warm floors. A simplified design procedure* for an individual duct sys tem is summarized as follows: 1. Calculate the heat loss of each room or area using the Warm Air Heating Systems Table 3.... Minimum Diffuser Free Area Required for Perimeter-Loop Systems 241 Length of feeder Duct under Room Plus length of Perimeter Dvcf Undsr Room, Ft. Hoot loss of Room Stub 0-9 Ft. 10-19 a 20-29 a 30-39 Ft. 40-49 Ft. 50-59 Ft. 60-59 a 0 to 4,000 to 6,000 to 8,000 to 3,999 5,999 7,999 9,999 10,000 to 11,999 12,000 to 13,999 14,000 to 15,999 16,000 to 17,999 18.000 to 19,999 20,000 to 21,999 22,000 to 23,999 24,000 to 25,999 26,000 to 27,999 28,000 to 29,999 30,000 to 31,999 32,000 to 34,000 Total Diffuser Free Area Required for Room, Square Indies 20 32 27 23 18 43 39 34 29 25 20 55 50 45 41 36 32 27 66 61 57 52 48 . 43 38 77 72 68 63 59 - 54 60 88 84 79 75 70 66 61 100 95 91 86 82 77 72 111 106 102 97 93 88 84 122 118 113 109 104 100 95 134 129 125 120 116 111 106 145 140 136 131 127 122 118 156 151 - 147 142 138 ' 133 129 168 163 159 154 150 ' 145 141 179 174 170 165 161 156 152 190 185 182 176 173 167 164 Section B. Use this Table if length of Feeder which DeGvere Major Portloo of Warm Air to Room is from 10 to 20 Ft. 0 to 3,999 4,000 to 5,999 6,000 to 7,999 8,000 to 9,999 10,000 to 11,999 12,000 to-13,999 14,000 to 15,999 16,000 to 17,999 18,000 to 19,999 20,000 to 21,999 22,000 to 23,999 24,000 to 25,999 . 26,000 to 27,999 28,000 to 29,999 30,000 to 31,999 32,000 to 34,000 23 18 18 36 31 26 21 16 16 49 44 39 34 29 24 19 61 -- 56 51 46 41 36 31 73 68 63 58 53 48 43 86 81 76 71 66 61 50 99 94 89 84 79 74 69 111 106 ' 101 96 91 86 81 123 118 113 108 103 98 93 135 130 125 120 115 110 105 148 143 138 133 128 123 118 161 156 151 146 141 136 131 174 168 164 158 154 148 144 186 181 176 171 166 161 156 198 194 188 184 178 174 168 211 206 201 196 191 186 181 Section C Use Thb Table if length of Feeder which DeGvers Major Portion of Worm Air to Room b from 20 to 30 Ft. 0 to 4,000 to 6,000 to 8,000 to 3,999 5,999 7,999 9,999 10,000 to 11,999 12,000 to 13,999 14,000 to 15,999 16,000 to 17,999 18,000 to 19,999 20,000 to 21,999 22,000 to 23,999 ' 24,000 to 25,999 26,000 to 27,999 28,000 to 29,999 30,000 to 31,999 32,000 to 34,000 27 21 21 42 36 30 24 18 57 51 45 39 33 27 21 72 66 60 54 48 42 36 86 80 74 68 62 56 101 95 89 83 77 71 116 110 104 98 92 86 131 125 119 113 107 101 50 65 80 95 145 139 133 127 121 115 100 160 154 148 142 136 130 124 175 169 163 157 151 145 139 190 184 178 172 166 160 154 205 199 193 187 181 175 169 220 214 208 202 196 190 184 234 22S 222 216 210 204 198 249 243 237 231 225 219 213