Document 96GKVN4N1gJRwx09LNL9eLNp

m 582 CHAPTER 24 1955 Guide fa - 0 F fa - 10 F - 20 F fa = 30 F Rate of Snowfall $ Velocity V -- . .Velocity v Velocity 0 5 10 15 5 10 15 5 10 15' 5 10 15 0.08 1.0 151 108 205 135 260 162 127 97 168 117 209 138 102 85 128 97 154 no 75 70 84 75 94 79 0.0 66 66 66 64 64 64 62 62 62 60 60 60 66 66 66 65 65 65 64 64 64 63 63 63 1.6 > 218 273 327 193 233 274 165 191 217 135 144 154 142 169 198 129 149 170 117 129 142 100 105 109 0.0 133 133 133 129 129 129 125 125 125 121 121 121 fm 99 99 99 97 97 97 95 95 95 93 93 93 1.0 292 347 401 1 265 305 346 235 261 287 203 212 221 fm 179 206 234 165 186 206 151 163 176 134 139 144 0.0 208 208 208 202 202 202 195 195 195 188 188 188 tm 137 137 137 134 134 134 131 131 131 127 127 127 Note: This table is based on a relative numiauy oi ou perwm. iU( au m, vc**iK'-***'* -- Rate of snowfall, inches of water equivalent per hour (See Table 3). 4> = Free area ratio. -- Slab output, Btu per (hour) (square foot). -- Air temperature, Fahrenheit. tm ~ Fluid temperature, Fahrenheit. Based on construction as shown in Fig- 16. v = Wind velocity, miles per hour. approximate data for ethylene glycol without an inhibitor and for a light oil, see Table 5. For small installations requiring less than 1 hp pump capacity, it may be satisfactory to compute the pump head required from friction loss tables for hot water heating systems, as given in Chapter 22, and to cor rect for the effect of the anti-freeze solution. Generally, hydraulic tables are prepared for water at 60 F and, 10 to 15 year old pipe. Since the circuit will be closed and the pipe will not scale or deteriorate, the age allowance on the pipe will probably be a sufficient allowance for the anti-freeze. If there is no age allowance, but the table is for 60 F water, then the following allowances for heated anti-freeze solutions will be adequate: 1. For fluid temperatures less than 100 F, add 15 percent. 2. For fluid temperatures between 100 and 130 F, add 10 percent. 3. For fluid temperatures above 130 F, no allowance. If friction data for higher temperature water are used as a basis, the allowances needed will be much greater. If the system is operated intermittently, fluid temperatures may drop to the freezing protection point. At that temperature, the fluid may be so viscous as to prevent the pump from discharging. If such conditions are expected the pump manufacturer should be consulted for advice w selecting the pump. Another allowance must be made in sizing the pump for anti-freeze; the volume of fluid to be pumped must be increased because of its 1?"' specific heat. Table 5 lists typical specific heat values, but here again, Panel Heating 583 on large jobs the manufacturer should be consulted for accurate data on his product. INSTALLATION There are certain precautions that must be taken during installation. They concern internal corrosion, flammability, toxicity, cleaning, joints, and hookup. A comprehensive discussion of these precautions may be found in Reference 8.' Safety Since ethylene glycol is slightly toxic, the system should be installed and maintained independently. There should be no permanent connec tion between the snow melting system and the drinking water supply. Table 5. Physical Phoferties of Anti-freeze Solutions Solution Freezing Protection Temp., F. % By Volume- Item Fluid Temperature, F 80 120 160 200 ** X 10* 1.92 1.14 0.77 0.56 0 31.4 e 0.839 0.854 0.874 0.899 to 65.1 64.4 63.6 62.7 Ethylene Glycol* --20 42.7 P X 10` e to 2.55 0.813 66.0 1.46 0.832 65.3 0.95 0.856 64.4 0.68 0.883 63.4 --40 51.2 ** X 10* to 3.16 0.788 66.8 1.77 0.809 65.9 1.14 0.835 65.0 0.80 0.866 64.0 Light Oilb -40 100 n X I0` c to 5.60 0.426 60.7 3.13 0.444 59.8 2.06 0.462 59.0 -- l- . rrom oocony-vacuum ou Uo. c- ty' ('?et ?er 8"n<b (Air. for oil at 80 F, ,, = 0.000056 ft> per sec.) specific heat, Btu per (pound) (Fahrenheit degree). w -- specific weight, pounds per cubic foot. . 1.50 0.479 58.1 Ethylene glycol is not considered flammable. In fact, aqueous solu tions of less than 60 percent glycol are used for fire sprinkler systems. These solutions do not freeze, and they are effective fire extinguishing agents. Petroleum distillates suitable for fluids in snow melting systems are classified as non-flammable, but have a flash point between 260 and 280 F. When using fluids of this type, care should be taken to collect any oil dripping from the packing seal on the pump. Internal Corrosion Ethylene glycol solutions tend to become corrosive in service; therefore, rust inhibitors are generally included. Even with an inhibitor, the solu tion should be tested annually to determine any change in acidity. If the test indicates that the inhibitor has been exhausted, the entire system should be drained and a fresh solution installed. To increase the life of the inhibitor, the heat exchanger surfaces should