Page:Steam heating and ventilation (IA steamheatingvent00monrrich).pdf/75

 The table also gives the amount of surface which was installed in each of the four rooms, and which has given perfect satisfaction throughout two or three severe winters. The radiator used was the two-column cast-iron radiator, 32 inches high, except in room 2, which had a 26-inch flue radiator. The radiation in room 2 was made slightly less than the amount calculated, because a large portion of the wall surface was a 25-inch brick wall, for which the multiplier for $$W\,$$ might be taken about 0.15 instead of 0.25.

It might be stated that in using the formula given, $$t_1\,$$ is to be taken 10 degrees above the lowest recorded temperature, and the factor, $$J\,$$, should be taken from 1.05 to 1.15 for severe exposures, and may also be increased 0.1 for ordinary brick buildings with wooden floor joists, and 0.2 for wooden buildings. The factor $$a\,$$ is to be taken at 1.7 for ordinary conditions of exhaust-steam heating. It may be increased somewhat for heating at higher pressures and for buildings with low-pressure heating and no power, in which steam pressure of 10 or 15 pounds may be carried, it may be made equal to 1.8. In such cases, also, the temperature, $$T\,$$, may be taken at 235 degrees. The factor a should be decreased where the radiators are of an unfavorable pattern or are unfavorably located, according to their relative heat-giving power, under such conditions as has been pointed out in Chapter III. The last part of the formula need be calculated but once for each building. The factor a may be taken as high as 2.8 in some greenhouses and in some factories in which wrought-iron pipe coils are used, which are quite an effective type of surface. Unless the coils are especially favorably located, however, the factor should be somewhat less than 2.8.

In the general application of the formula given above it will be noted that the expression $$(t - t_1 ) (1.3 G + 0.25 W + 0.008 C)\,$$ represents the total heat given off by the room, and it is equal to $$R (T - t) a\,$$, which is the heat given off by the radiation surface.

Mr. Wolff in his practice calculates the heat lost per hour from each room according to his diagrams previously given, with the allowance for exposure as shown thereon. He then (divides this amount by the number of British thermal units given off per