Document 6b3rNM4G6bgwrJ6LBMoDR5db9

American Society of Heating arid Ventilating Engineers Guide, 1937 Chapter 9--Central Systems for Heating and Humidifying water sprays will become partially saturated (adiabatically) having a moisture con1 toer pound of air equal to saturated air at 41 F. If the incoming air is warmed to tenl Rg F [requiring a two-section-depth heating unit) it will be cooled in the washer to 64 F, with a temperature drop of 88 - 64 = 24 deg. the humidifying efficiency of the washer were 100 per cent, the air would become ,. batically saturated at 52 F after a temperature drop of 88 -- 52 =. 36 F. The aJ 0f the washer is, however, only 67 per cent, so that the actual temperature drop STo 67 X 36 deg or 24 deg, as used. The heat to be supplied the reheater is in this case Hi = 0.24 (ij -- 64) M Btu per hour and the heat to be supplied to the tempering coil and preheater is Hi = 0.24 (88 -- fc) M. The total heat required by the apparatus is Hi '+ Hi, no heat being supplied to the washer. Case D. (Fig. 6) The maximum relative humidity that may be maintained within the building without the precipitation of moisture on single glazed sash when the outside temperature is 30 F ^ approximately 35 per cent. If the inside temperature t is 70 F, 35 per cent relative humidity corresponds to a dew-point temperature of 41 F. (See psychrometric chart.) The installation shown in Fig. 6 contemplates the use of a tempering coil, an'air washer provided with a water heater, and a reheater. The tempering coil, one section in depth, warms the incoming air to approximately 35 F to prevent freezing any of the spray wpter; The air passing through the spray chamber is saturated and leaves at a tempera ture of h = 41 F: The heat to be supplied the reheater is: Hi = 0.24 (h -- 41) M Btu per hour. The heat to be supplied the tempering coil is: . Hi = 0.24 (35 -- to)M Btu per hour. ...The amount of heat, per pound of air circulated, to be supplied the humidifying washer of humidifier is the difference between the heat content of the assumed' dry air entering the washer at a temperature of tv == 35 F and that of the leaving saturated air at <1 = 41 F (Table 6, Chapter 1), or: 15.657 -- 8.397 = 7.26 Btu per pound of dry air. ,Tho amount of heat required for the washer is: f l; ' l: ` Hi = 7.26 M Btu per hour. / \ -v -i. ' . - . The-totaUci.mount of. heat required by the apparatus is, therefore: Hi + Hi + Hi Btu per hour. If 4f^sh'er Having a Humidifying efficiency of 67 per cent without water heater is eroployed'ii wiU be necessary to heat the outside air drawn into the apparatus by means of the tempering, and preheater coils to such a temperature that the air in passing through 180 Fig. 7. Outside Air Circulated; Constant Temperature and Relative Humidity Maintained in Each Room (Case B) Case E. (Fig. 7) The temperature ty will ordinarily be different f6r each room. With H and M fixed, 0.24 (ty -- t)M = H, or H h = o.24 M + ` In order to provide the proper temperature for each room, a booster coil is generally installed in each supply duct near the outlet to control the out let temperature ty. The amount of steam supplied to these booster units is usually controlled automatically by individual thermostats. The heat required by the booster coils depends on the temperature range through which the air is heated and the quantity of air, or H, = 0.24 (ty - h - h)M ", (13) Heat to be Supplied " The amount of heat to be supplied (H1) is equal to the sum of the heat requirements of the various heating units and the water heater of the washer, if any, plus the allowance for piping tax. . (See preceding Cases A to E.) 181