Document emJq8GkJ83aZm7ebqO7ooBK2M

628 CHAPTER 23 195? Guide' CQiAit (24) where C = pump capacity, pounds per hour. ' Af = area of slab, square feet. qt = total heat requirement (slab output, g0, plus back and edge losses) Btu per (hour) (square foot). Cm = specific heat at temperature tm, Btu per (pound) (Fahrenheit degree). Ai = temperature drop through circuit, Fahrenheit degrees. KINEMATIC VISCOSITY, SO. FT/SEC fx 10s) Fig. 21. Friction Correction Factor for Viscosity (For Nr, > 3000) For a temperature drop of At = 20 F, Equation 24 becomes G= lGOtPmCm (25) where G = gallons per minute. Wm = mean specific weight at temperature tm, pounds per cubic foot. An approximate solution for systems using pipe sizes other than 1-in. IPS can be obtained by using Table 10 or Fig. 21. Table 10 is for use; when the flow is in the laminar zone. Fig. 21 is for flow in the turbulent -. zone. For flows where Reynolds number falls between 2000 and. 3000, no reliable prediction for pressure loss can be made. It is generally safe to assume the flow to be increased to a Reynolds number of 3000 with the. pressure loss estimated at that flow rate. Figure 20 is based on a pipe size of 1 in. IPS. If another pipe size is used and the flow is laminar, the correction factor K from Table 10 can be used. Panel Healing 629 Table 6. Heat Output and Fluid Temperature for Snow Melting Systems s Rate or Snowfall Ba t. = 01? Velocity V 5 10 15 tt = 10 F Velocity V 5 10 15 U = 20 F Velocity V 5 10 15 U = 30 F Velocity V 5 10 15 0.08 1.0 Qo 151 205 260 127 168 209 102 128 154 75 84 94 108 135 162 97 117 138 85 97 110 70 75 79 0.0 Qo 66 66 66 64 64 64 62 62 62 60 60 60 66 66 66 65 65 65 64 64 64 63 63 63 0.16 1.0 Qo 218 273 327 193 233 274 165 191 217 135 144 154 142 169 198 129 149 170 117 129 142 100 105 109 0.0 Qo 133 133 133 129 129 129 125 125 125 121 121 121 99 99 99 97 97 97 95 95 95 93 93 93 0.25 1.0 Qo 292 347 401 265 305 346 235 261 287 203 212 221 im 179 206 234 165 186 206 151 163 176 134 139 144 0.0 Qo 208 208 208 202 202 202' 195 195 195 188 188 188 137 137 137 134 134 134 131 131 131 127 127 127 Note: This table is based on a relative humidity of 80 percent for all air temperatures. * = Hate of snowfall, inches of water equivalent per.hour (See Table 5). Rh = Free area ratio. Qo = Slab output, Btu per (hour) (square foot). t* = Air temperature, Fahrenheit. 83 Fluid temperature, Fahrenheit. Based on construction as shown in Fig. 19. = Wind velocity, miles per hour. For example, assume a viscosity of 300 SSU, a flow of 5 gpm and a %-in. inn ,pipe' Fig. 20 shows that for 1-in. IPS, friction loss would be 15.50 ft/ 100 ft. Table 10 gives K = 2.62 for %-in. pipe; therefore, friction loss would be 15.5 X 2.62 = 40.6 ft/100 ft. If the flow is in the transition zone or is turbulent, then Fig. 2 of Chapter 21 can be used in conjunction with Fig. 21. For example, assume a vis- 0.0001 sq ft/sec. (56.5 SSU), a flow rate of 14 gpm and a 1%-in. . pipe size. Fig. 2, Chapter 21, shows a head loss for water to be 190 nunneries per foot or 1.58 ft/100 ft,' ' Figure 21 gives a correction factor K , ,,V'5 for a viscosity of 0.0001 sq ft/sec; hence, the pressure loss is 1.58 X 1.75 = 2.77 ft/100 ft. INSTALLATION There are certain precautions that must be taken during installation, hey concern internal corrosion, flammability, toxicity, cleaning, joints, "Uu hookup. A comprehensive discussion of these precautions mav be round in Reference 17. Safety Since ethylene glycol and petroleum distillates are slightly toxic, , the ystem should be installed and maintained independently. There should no permanent connection between the snow melting system and the unnking water supply. Ethylene glycol is not considered flammable. In fact, aqueous soluns of less than 60 percent glycol are used for fire sprinkler systems.