Document jyYJkRJK4EeoexkvG8KYkxwxQ

488 CHAPTER 19 1957 Guide Table 5. Heating Capacities and Cfm of Branch Ducts in Extended Plenum Perimeter Systems (Concluded) SECTION E. SIDE TAKEOFF TO 6-INCH ROUND PIPE FOR SIDEWALL AND FLOOR DIFFUSERS Extended Plenum Pressure OAt in.- Static at 160 F Furnace Plenum Pressure 0A6 in. Static at 170 F No. op Elbows Actual Length prom Extended Plenum to Diffuser---Feet 5 10 15 20 25 30 35 40 45 50 55 60 0 Btuh Cfm 8600 7930 7310 6740 6230 5800 123.2 120.0 116.8 114.0 111.4 109.1 1 Btuh Cfm 8560 7900 7290 6720 6200 5740 5340 117.4 114.5 112.1 109.2 107.0 104.8 102.8 2 Btuh Cfm 8510 7890 7300 6740 6230 5750 5310 4960 112.7 110.0 107.6 105.3 103.1 101.0 99.0 97^ 3 Btuh Cfm 8540 7900 7300 6780- 6270 5800 5360 4960 4610 108.2 105.8 103.6 101.5 99.6 97.8 95.9 94.0 92.5 4 Btuh am 8580 7970 7370 6820 .6330 5850 5410 5000 4620 4300 104.0 101.9 99.8 97.8 96.0 94.5 92.8 91.1 89.7 88.3 5 Btuh am 8720 8080 7490 6940 6440 5960 5490 5080 4690 4320 4020 100.2 98.3 96.7 94.8 93.0 91.4 90.0 88.7 87.2 85.0 84.7 6 Btuh 8900 8240 7630 7060 6550 6070 5600 5190 4800 4430 4100 3810 Cfm 97.0 95.1 03.4 91.9 90.2 88.8 87.3 86.2 85.0 83.8 82.6 81.5 Note: Where any of the first three runs from the extended plenum'exceeds 20 ft and 3 elbowB, count 3 extra elbows for that run. The Equivalent Length Values used and included in calculating this table are: Diffuser and Boot = 40 t; Each Elbow = 14 ft; Side Takeoff = 20 ft. Tapered Extended Plenum Starting Collar. SECTION F. TOP TAKEOFF TO 6-INCH ROUND PIPE FOR SIDEWALL AND FLOOR DIFFUSERS Extended Plenum Pressure 0.18 in. Static at 160 F Furnace Plenum Pressure 0.16 n. Static at ITOF Elbows Actual Length fbom Extended Plenum to Diffuses--Feet 5 10 15 20 25 30 35 40 45 50 55 60 0 Btuh Cfm 8430 7800 7210 6660 6170 5700 111.2 108.8 106.3 104.4 102.2 100.2 5270 98.4 4910 96.7 1 Btuh Cfm 8450 7840 7250 6700 6210 5730 5300 4900 4560 107.2 105.0 102.8 100.7 98.9 97.0 95.1 93.4 91.9 2 Btuh am 8530 7900 103.2 101.1 7320 99.0 6800 97.2 6280 95.4 5790 93.8 5350 92.1 4960 90.6 4590 89.0 4250 87-8 3 Btuh Cfm 8660 99.7 8020 97.8 7430 96.0 6900 94.2 6370 92.4 5900 90.8 5450 89.4 5030 88.0 4650 88.7 4300 85.3 3990 84.2 4 Btuh Cfm 8810 96.0 8180 94.4 7580 92.8 7010 91.2 6500 89.7 6000 88.0 5550 86.8 5150 85.7 4750 84.3 4400 83.1 4070 82.0 3780 81.1 5 - Btuh Cfm 8390 91.4 7770 90.0 7200 88.5 6650 87.2 6160 85.8 5700 84.5 5280 83.2 4890 82.4 4500' 4170 81.0 80.0 3840 79.0 3580 78.3 6 Btuh am 7980 87.5 7380 86.2 6840 85.0 6340 83.8 5880 82.5 5430 81.4 5020 80.2 4650 79.4 4290 78.3 3970 77.3 3660 76.3 3400 75.6 Note: Where any of the first three runs from the extended plenum exceeds 20 ft. and 3 elbows count.3 extra elbows for that run. The Equivalent length Values used and included in calculating this table are: Diffuser and Boot ft; Each Elbow = 14 ft; Top Takeoff = 50 ft. Tapered Extended Plenum Starting Collar. Warm Air Heating Systems 489 Table 6. Required Size of Extended Plenum Cfm Handled bt Plenum Plenum Dimen sions Inches Cfm Handled bt Plenum Plenum Dimen sions Inches Up to 300 301 to 400 401 to 500 .501 to 600 601 to 700 8x8 10x8 12 x 8 14 x 8 16 x 8 701 to 800 801 to 900 901 to 1000 1001 to 1100 1101 to 1200 20 x8 22x8 24 x 8 26x8 28 x 8 Design of Return Duct System for Perimeter Installations With perimeter systems designed in accordance with the foregoing sim plified procedures, there is a circulating head of only 0.05 in. water avail able on the return side of the system. It is therefore necessary that the return ducts be adequately sized and be as short and straight as practica ble. The return grilles may be centrally located, and the ducts may be located in the attic or other unheated spaces provided they, are adequately insulated. Return air may be taken from basements and crawl spaces, but should not be taken from confined spaces in which the furnace is located. The following simplified procedure6 may be used: 1. Lay out the return-air duct system. Measure the length and count the num ber of 90 deg turns in each return duct. 2. Total the heat loss of the area served by each return duct. 3. Determine the required duct free area from the length of duct, the number of 90 deg turns, and the heat loss using Table 7. Also determine the free area of the return grille from Table 7. Other Perimeter Systems Each of the foregoing procedures can be used with approved furnaces which are capable of delivering their rated cfm air volume against a total Table 7. Required Size of Return Air Grille and Duct For Pressure Drop Allowance of 0.06 In. of Water Actual Ft. Q No. OF 90 Deg m < Purns 3H *< O Btuh Up to 10 Ft 23456 11 to 20 Ft 21 to 30 Ft 23456 1 23456 Duct Free Area 31 to 40 Ft 2 3 45 6 16 5,000 14 17 20 23 26 28 15 19 22 25 27 28 17 20 23 25 27 29 18 21 24 27 28 30 10,000 27 32 37 42 46 46 26 34 39 43 47 48 31 36 41 45 48 51 33 38 43 47 46 51 15,000 37 44 5(1 55 60 64 40 46 52 57 61 65 43 48 54 58 63 67 45 51 56 61 64 67 20,000 46 54 61 66 73 78 49 67 63 69 75 79 53 60 65 71 77 82 55 62 68 74 78 83 79 25,000 54 64 72 79 86 92 58 68 75 82 88 94 62 71 78 84 91 96 66 74 80 87 92 98 30,000 62 73 82 89 97 104 67 76 85 93 100 106 71 80 88 95 102 108 75 84 91 99 104 110 126 35,000 69 82 92 101 111 119 74 85 95 106 114 121 79 91 99 108 117 124 84 94 103 113 116 126 40,000 77 90 100 110 121 130 82 94 105 116 124 132 87 99 109 118 128 137 92 103 113 123 130 140 158 50,000 89 105 119 132 146 158 95 111 124 138 150 161 102 117 129 142 155 166 108 123 135 148 158 170 60,000 100 122 m 154 170 181 111 129 145 161 174 184 119 137 151 165 178 189 126 143 158 172 181 193 70,000 117 139 158 174 191 203 127 147 164 182 195 206 136 155 171 186 200 213 144 162 178 193 203 216 128 155 175 191 208 222 140 164 182 198 214 225 161 172 188 203 219 231 160 179 195 211.222 235 284 90,000 141 168 188 205 225 244 153 177 *195 213 232 248 164 166 201 218 240 256 173 193 209 229244 262 154 180 200 221 247 265 166 189 209 233 252 270 176 198 217 239 258 277 185 206 227|250265 285 Ksther to dS*ere-a ""hip*6 number of return air ducta join together, add the individual duct free areas toaeermine the free area of duct to be used from that point to the return air plenum of furnace.