We already know that one B. T. U. will raise the temperature of 1 cubic foot of air 55 degrees, or it will raise 100 cubic feet 1/100 of 55 or 55/100 of 1 degree, therefore to raise 100 cubic feet 1 degree it will take 1/ 55/100 or 100/55 B. T. U., and to raise 100 cubic feet through 100 degrees it would take 100/55 X 100 B. T. U. In other words, the B. T. U. required to raise any given volume of air through any number of degrees in temperature is equal to

Volume of air in cubic ft. X Degrees raised / 55

150 H.P. DE LAVAL TURBINE BL0WER.

Example - How many B. T. U. are required to raise 100,000 cubic feet of air 70 degrees ?

100,000 X 70 = 127,272 +

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To compute the H. P. required for the ventilation of a building we multiply the total air supply in cubic feet per hour by the number of degrees through which it is to be raised, and divide the result by 55. This gives the B. T. U. per hour, which divided by 33,000 will give the H. P. required. In using this rule always take the air supply in cubic feet per hour.

Example. - A high school has 10 class rooms, each occupied by 50 pupils. Air is to be delivered to the rooms at a temperature of 70 degrees. What will be the total H. P. required to heat and ventilate the building when it is 10 degrees below zero if the heat loss through walls and windows is 1,320,000 B. T. U. per hour?

Cubic feet of air = 3000 X 10 X 50 = 1,500,000

To heat this quantity we need

1,500,000 X 80 = 2,181,800 B. T. U. 55

Total B. T. U. = 1,500,000 + 2,181,800 = 3,501,800

Boiler H. P. = 3,501,800/ 33,000 = 106. Ans.