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570 CHAPTER 24 1954 Guide 3r 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 perceot. 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 alloIfwathnecessynseteemdedisw' oipllebraetemduicnhtegrrmeaittteer.ntly, fluid temperatures may drop to the; freezing protection point. At that temperature, the fluid may be Table 5. Physical Peoperties of.Anti-freeze Solutions Solution Freezing Protection. Temp., F. %Bt Volume 31.4 Item <1 X 10* Fluid Tempebatube, F 120 160 200 1.92 0.839 65.1 1.14 0.854 64.4 0.77 0.874 63.6 0.56 0.899 62.7 Ethylene Glyool 42.7 M X 10* 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 P X 10` 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 It x 10` 5.60 0.426 60.7 3.13 0.444 59:8 2.06 0.462 59.0 1.50 0.479 58.1 p In=tekrpinoelamteadticfrvoismcoRseitfye,re(fneceet9s.quarbedFrpoemr seScoocnodn)y(-eV.pa.cfuourmoiOl ailtC80o.F, a =" 0.000056 ft* per sec.) c ~ specific heat, Btu per (pound) (Fahrenheit degree). re * specific'weight, pounds per cubic foot. so viscous as to prevent the pump from discharging. If such conditions are expected the pump manufacturer should be consulted for advice in seAlenctointhgetrhealplouwmapn.ce must he made in sizing the pump for anti-freeze; the volume of fluid to be pumped must be increased because of its low specific heat. Table 5 lists typical specific heat values, but here again, on large jobs the manufacturer should be consulted for accurate data on hisproduct. 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. SaSfeintyce 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 arid the drinking water supply- Panel Heating 571 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 be kept below 285 F which corresponds to about 40 psig steam. Tempera tures above 300 F accelerate the deterioration of the inhibitors; Slab Construction___ It has been found satisfactory to use % pipe or tubing on 12-in. centers as a standard coil. If pumping-loads require a reduction in friction the pipe size may be increased to 1-in., but the slab depth must be increased ac cordingly. The piping should be supported in such a manner that there is a minimum of 2 in. of concrete aboye and below the pipe. This requires a 5-in. slab for %-in. pipe and 5%-in. for 1-in. pipe. If an insulating material is used; it is generally good practice to provide a moisture barrier between the insulation and the fill; A roofing material (such as a 55 lb. felt) is often used as a moisture barrier; The joints should be mopped, and the fill made smooth enough so that there will be no holes or gaps for moisture transfer. Also, the edges of the barrier should be flashed to the surface of the slab so that the ends are sealed. See Fig. 16. If the pipe must pass through an expansion joint,' a protective coating should be applied to the pipe for a foot or two on both sides of the joint. If the pipe is kept dry at all times in both summer and winter, no ex ternal corrosion problems will occur. Draining Proper drainage is necessary for both the slab surface and the coil. The slab must be sloped so that the water from the melted snow can nm off. Puddles are objectionable on sidewalks or drives. They cause splashing, and they retard heat flow from the embedded pipes. The pipes must be placed so that they may be drained. If the anti freeze becomes corrosive .it must be drained. It is not good practice to rely entirely on blowing of air through the system. Drifting Snow It is quite likely that some drifting will occur on every system that is adjacent to a wall or vertical surface. The designer should try to antici pate this condition and add extra piping in these areas. If possible, coils should be added in the vertical surface. Another expedient is to carry