Cyclopedia of heating, plumbing and sanitation; a complete reference work . olumes ol Air by Either Steam or Hoi Wat* r. depends upon its form, tin1 difference in temperature between thesteam and the surrounding air, and the velocity with which the airpasses over the heater. Under ordinary conditions in dwelling-housework, a good form of indirect radiator will give off about 2 B. T. square foot per hour foreach degree difference in tem-perature between the strainand the enteringair. Assum-ing a .-team pressure of 2pounds and an outside tem-perature of zero, we shouldhave a difference in
Cyclopedia of heating, plumbing and sanitation; a complete reference work . olumes ol Air by Either Steam or Hoi Wat* r. depends upon its form, tin1 difference in temperature between thesteam and the surrounding air, and the velocity with which the airpasses over the heater. Under ordinary conditions in dwelling-housework, a good form of indirect radiator will give off about 2 B. T. square foot per hour foreach degree difference in tem-perature between the strainand the enteringair. Assum-ing a .-team pressure of 2pounds and an outside tem-perature of zero, we shouldhave a difference in tempera-ture of about 220 degrees,which, under the conditionsstated, would give an efficiencyof 220 X 2 = 440 B. T. hour for each square footof radiation. By making a similar computation for 10 degrees be-low zero, we find the efficiency to be 400. In the same manner wemay calculate the efficiency for varying conditions of steam pressureand outside temperature. In the case of schoolhouses and similarbuildings where large volumes of air are warmed to a moderate tem-. Fig. 57. End View of Several School PinRadiator Sections Connected Together. 84 HEATING AND VENTILATION 75 perature, a somewhat higher efficiency is obtained, owing to the in-creased velocity of the air over the heaters. Where efficiencies of 4 Wand 460 are used for dwellings, we may substitute 600 and 620 forschoolhouses. This corresponds approximately to B. T. I . persquare foot per hour for a difference of 1 degree between the air and steam. The principles involved in indirect steam heating are similarto those already described in furnace heating. Pan of the heat givenoff by the radiator must be used in warming up the air-supply to thetemperature of the room, and part for offsetting the loss by conductionthrough walls and The method of computing the heatingsurface required, depends upon the volume of air to be supplied to theroom. In the case of a schoolroom or hall, where the air quantity SID
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