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American Society of Heating and Ventilating Engineers^CJuide, 1935 Table 10. Coefficients of Transmission (IT) for Pipes Insulated with Rock Wool Type Insulation j These coefficients are expressed in Btu-per hour per square foot of pipe surface per degree Fahrenheit difference in temperature between pipe and surrounding still air at 70 F Thickness or Insulation (Inches) 1 Nominal . Pipe Size (Inches) A ' SA 1 m 1A 2 2a 3 3A 4 i'A 5 6 8 10 12 120 F SOT 0.631 0.569 0.518 0.476 0.450 0.422 0.402 0.385 0.373 0.363 0.355 0.348 0.341 0.327 0.317 0.313 Hot Water 210 F | 150 F 80 F 180 F 227.1 F (5 Lb) Temperature Difference 110 140 r 157.1 0.644 0.581 0.529 0.486 0.460 0.431 0.411 0.394 0.381 0.371 0.363 0.356 0.348 0.335 0.324 0.320 0.658 0.593 0.541 0.497 0.470 0.441 0.420 0:402 0.389 0.379 0.371 0.364 0.356 0.342 0.331 0.327 0.672 0.606 0.552 0.507 0.480 0.450 0.428 0.411 0.398 0.387 0.379 0.371 0.363 0:349 0.338 0.334 0.680 0.613 0.559 0.513 0.485 0.456 0.434 0.415 0.402 0.392 0.383 0.376 0.368 0.353 0.343 0.338 Steam 297.7 F (50 Lb) 337.57* (lOOLb) 227.7-F 267.9 F' 0.712 0.730~ 0.642 0.659 0.585 0.600 0.537 0.551 0.508 0.522 0.478 0.490 . 0.455 0.466 0.435. 0.446 0.421 0.432 0.411 0.422 0.402 . .0.413 0.394 0.404 0.386 0.396 0.372 0.381 0.360 0.369 0.355 0.364 A 0.523 0.534 0.545 0.556 0.563 0.590 0.606 H 0.468 0.477 0.487 0.497 0.503 0.528 0.542 1 0.421 0.430 0.440 0.449 0.455 0.477 0.490 m 0.383 0.391 0.399 0.407 0.412 0.433 0.444 m 0.359 0.366 0.375 0.383 0.387 0.407 0.419 2 0.333 0.340 0.348 0.356 0.360 0.378 0.389 m 0.314 0.320 0.327 0.335 0.339 0.355 0.365 3 0.296 0.302 0.310 0.317 0.321 0.337 0.347 m 3A 0.286 0.291 0.298 0.304 0.307 0.323 0.332 4 0.278 0.284 0.290 0.296- -0.300 0.315 0.323 *A 0.270 0.276 0.282 0.287 0.291 0.305 0.313 5 0.263 0.269 0.275 0.280 0.284 0.298 0.305 6 0.257 0.262 0.267 0.273 0.277 0.290 0.297 8 . 0.244 0.249 0.254 0.260 0.263 0.276 0.283 10 0.235 0.240 0.245 0.250 0.253 0.265 0.272 12 0.230 0.234 0.239 0.245 0.247 0.260 0.267 A 0.461 0.471 0.481 0.491 0.496 0.520 0.534 3A 0.409: 0.418 0.427 0.436 0.441 0.463 0.475 .1 0.366 0.374 0.382 0.390 0.395 0.415 0.427 0.333 0.340 0.347 0.355 0.359 0.377 0.387 m 0.310 0.316 0.323 0.330 0.334 0.351 0.360 2 0.286 0.292 0.298 0.304 0.308 0.323 0.331 2A 0.268 0.274 0.279 0.285 0.289 0.302 0.310 3 0.252 0.257 0.262 0.268 0.272 0.284 0.292 2 3A 0.241 0.246 0.251 0.257 0.260 0.272 0.280 4 0.232 0.237 0.242 0.247 0.250 0.262 0.269 IA 0.225 0.230 0.235 0.240 0.243 0.255 0.262 5 0.218 0.223 0.228 0.233 0.236 0.247 0.253 6 0.213 0.217 0.221 0.226 0.228 0.239 0.245 8 0.200 0.204 0.208 0.213 0.215 0.225 0.231 10 0.189 0.193 0.197 0.201 0.204 0.214 0.220 12 ' : 0.185 0.190 0.194 0.198 0.200 0.210 0.216 630 Chapter 36--Insulation of Piping on F- the thickness of insulation for brine is approximately 234 in. where ^/temperature ranges from 0 deg to 25 F; and the thickness of insulation where the brine temperature ranges from -- 30 F to zero degrees is ap proximately 4 in. Insulation To Prevent Freezing If the surrounding air temperature remains sufficiently low for an Dle period of time, insulation cannot prevent the freezing of still water, nr of water flowing at such a velocity that the quantity of heat earned in the water is not sufficient to take care of the heat losses which will result and cause the temperature of the water to be lowered to the freezing ooint Insulation can materially prolong the time required for the water to give up its heat, and if the velocity of the water flowing in the pipe is maintained at a sufficiently high rate, freezing may be prevented. Table 11 may be used for making estimates of the thickness of insula tion necessary to take care of still water in pipes at various water and surrounding air temperature conditions. Because of the damage and service interruptions which may result from frozen water in pipes, it is essential that the most efficient insulation be utilized. This table is based on the use of hair felt or cork, having a conductivity of 0.30. The initial water temperature is assumed to be 10 deg above, and the sur rounding air temperature 50 deg below the freezing point of water (tem perature difference, 60 F). The last column of Table 11 gives the minimum quantity of water at initial temperature of 42 F which should be supplied every, hour for each linear foot of pipe, in order to prevent the temperature of the water from being lowered to the freezing point. The weights given in this column should be multiplied by the total length of the exposed pipe line expressed in feet. As an additional factor of safety, and in order to provide against temporary reductions in flow occasioned by reduced pressure, it is advisable to double the rates of flow listed in the table. It must be emphasized that the flow rates and periods of time designated apply only for the conditions stated. To estimate for other service conditions the following method of procedure may be used. If water enters the pipe at 52 F instead of 42 F, the time required to cool it to the freezing point will be prolonged to twice that given in the table, or the rate of flow of water may be reduced so that the quantity required will be one-half that shown in the last column of Table 11. However, if the water enters the pipe at 34 F it will be cooled to 32 F in one-fifth of the time given in the table. It will then be necessary to in crease the rate of flow so that five times the specified quantity of water will have to be supplied in order to prevent freezing. If the minimum air temperature is -- 38 F (temperature difference, 80 F), instead of -18 F, the time required to cool the water to the freezing point will be 60/80 of the time given in the table, or the necessary quantity of water to be supplied will be 80/60 of that given. In making calculations to arrive at the values given in Table 11, the loss of heat stored in the insulation, the effect of a varying temperature dif ference due to the cooling of pipe and water, and the resistance of the outer surface of the insulation to the transfer of heat to the air have all 631