Document 06yn224j0MjqDmG7BvEX0332d

Amebican Society of Heating and Ventilating Engineers Guide, 1930 Chapter 21--Piping for Hot Water Heating Systems Maximum Water Temperature It is the custom to select 180 deg. as the maximum temperature of the water, leaving the heater. With this maximum temperature and a tem perature drop of 20 deg. through the radiator, the average water tempera ture in the radiator will be 170 deg. If the temperature of the room is to be'70 deg., the temperature difference, water to air will be 100 deg. The corresponding value of U (see Fig. 2) for a 38-in., 3-col. radiator, is 1.34 and the heat dissipated by the radiator per square foot per hour is 134 B.t.u. A steam radiator of similar size and design and supplied with low-pressure steam will dissipate about 240 B.t.u. per square foot per hour. Under these conditions a hot water heating system would require about 240 sq. ft. of radiation for every 134 sq. ft. required by the steam heating system. The first cost of the hot water system would,, conse quently, be considerably greater than that of the corresponding: steam Fig. 1.. Six Different Methods of Piping a Heating System of<Four Radiators 368 Temperature difference Water 7o Air Fig. 2. Suggested Values for the Heat Dissipation Coefficients U of Various Types of Hot Water Radiators system. This higher first cost of a hot water system is frequently the cause of the installation of a steam system. ' If, on the other hand, 220 deg. is selected as the temperature of the water leaving the heater, the average temperature of the water in the radiator will be about 210 deg., practically the same as that in low-pressure steam radiation, and the total radiation required for the hot water system will be about the same as that required for the corresponding steam system. The cost of the pipe system for hot water is probably a little higher than the cost of the pipe system for steam, but the cost of valves and traps for a steam system is greater than the cost of the valves-for a hot water system, so that, finally, the cost of a hot water heating system will equal, or it may" be lower, than the cost of a corresponding steam heating system, if..the water temperature selected is sufficiently high. The selection of 220 deg. as the maximum water temperature is entirely 369