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10. Radiation.

10a. Coefficient of Transmission for Radiation.-Various tests have been made to determine the rate of transmisson for radiation under varying conditions of temperature. The best data are those given by J. R. Allen of the University of Minnesota from which Table 12 has been compiled. The factor K was calculated in each case above or below 150 deg. difference in temperature by applying a 0.2% correction. This table is applicable to hot water or steam systems, and gives transmission rates for all types of radiators and temperature differences.

Assume that a 3-column 38-in. radiator has a difference of 230-50 deg. = 180 deg. K, from actual test (150 deg. difference), has a value of 1.55 B.t.u. per sq. ft. per hr. per deg. difference. For 180 deg. difference the factor K will be 1.55+ 0.002 x (180-150) X 1.55 1.64 B.t.u. per sq. it. per deg. difference (see Table 12). Then 1.64 X 180 deg. = 295 B.t.u. per sq. ft.

U

=

The standard for rating direct radiation as used in manufacturers' catalogues, is 70-deg. F. room temperature, and 220 deg. F. inside the radiator, or 150 deg. F. difference between the room and the heating medium for steam. From Table 12 for a 3-column 38-in. radiator, U= 233 B.t.u. which, divided by 970 B.t.u. (the latent heat at atmospheric pressure) gives 0.24 lb. of steam condensed per sq. ft. per hr. Hot water boilers and radiators are rated for an average temperature of water of 170 deg. F. and 70 deg. F. in the room, or 150 B.t.u. For a 2-column 38-in. radiator

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The actual standard unit used in rating steam boilers is 4-lb. condensation per hr. per sq. ft. of radiationor 250 B.t.u. Hot water boilers are rated on the basis of 150 B.t.u. per sq. ft. of radiation per hr. If the temperature were the same for the medium, hot water would require no more radiation than steam.

106. Determination of Radiation.-Refer to typical plan, Fig. 7, and heat loss schedule, Table 13. The determination of the radiation should be independent of the medium

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where steam or water is used, as the only determining factor is the difference in the radiator and room temperatures. The first tabulation "A" is computed for the medium at a temperature of 210 deg. for 3-column 38-in. radiators and for coils on the fourth floor. The transmission factors for the radiators and coils are 213 B.t.u. and 274 B.t.u. per sq. ft. per hr. respectively, for 140-deg. difference as shown in Table 12. The total radiation required is 5452 sq., ft. and the radiating units needed for this tabulation are indicated on the plan (Fig. 7). The tabulation "A"" is calculated for 3-column 38-in. radiators on the fourth floor instead of coils, making 5788 sq. ft. of total radiation required. In the "B" schedule, water of 170-deg. average temperature was assumed and 2 column 38-in,. radiators (8221 sq. ft. required). In schedule "C" the temperature of the medium was assumed at 220 deg., or 4 lb. steam pressure, difference of 150 deg (5300 sq. ft. required). If the heat losses are reduced to square feet of radiation at 0.25 lb. condensation (250 B.t.u.), there would be 4930 sq. ft.

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Pipe coils.

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Wall radiator horizontal and 1 column 22 in..

1.72 138 1.76 158 1.80 180 1.84 2021.88 226 1.92 250 1.96 274 2.00 300 2.04 326 2.08 354 2.12 382 2.16 410 1.68 134 1.72 155 1.76 176 1.794 197 1.83 220 1.87 243 1.91 267 1.95 293 1.99 318 2.03 345 2.07 3732.11 401 Wall radiator vertical and 1 column 26 in. 1.63 130 1.67 150 1.71 171 1.75 193 1.79 215 1.82 237 1.86 260 1.90 285 1.94 310 1.98 337 2.01 362 2.05 390 1.59 127 1.63 147 1.67 167 1.7 187 1.74 209 1.78 231 1.81 253 1.85 278 1.89 302 1.92 326 1.96 353 2.00 380 1.55 124 1.584 143 1.62 162 1.656 182 1.69 203 1.73 225 1.76 246 1.8 270 1.84 294 1.87 318 1.91 344 1.94 369

1 column 32 in..

column 38 in.-2 column 22 in.

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1.51 121 1.54 139 1.58 158 1.61 177 1.64 197 1.68 218 1.72 241 1.75 263 1.79 286 1.82 309 1.86 335 1.89 359:

1.46 117 1.50 135 1.53 153 1.56 172 1.60 192 1.63 212 1.67 234 1.70 255 1.73 277 1.77 301 1.80 324 1.84 350
1.425 114 1.455 131 1.485 149 1.515 1671.55 186 1.59 207 1.62 226 1.65 248 1.71 274 1.75 297 1.77 319 1.815 345

1.38 110 1.41 1271.44 144 1.47 162 1.5 180 1.54 200 1.57 220 1.60 240 1.63 261 1.66 282 1.70 306 1.73 329
1.33 106 1.36 122 1.40 140 1.43 157 1.46 175 1.49 194 1.52 213 1.55 233 1.58 253 1.61 274 1.64 295 1.67 317
135 1.38 152 1.41 169 1.44 187 1.47 206 1.50 225 1.53 245 1.56 265 1.59 286 1.62 308

1.29 103 1.32 119 1.35

1.25 100 1.28 1151.31

131 1.33 146 1.36 163 1.39 181 1.42 199 1.45 217 1.48 237 1.51 257 1.54 277 1.57 298

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