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American Society `of Heating and Ventilating Engineers Guide, 1932 retained in the room if the product being manufactured is not removed until its temperature is the same as the room temperature. If power is transmitted to the machinery from the outside, then only the heat equivalent of the brake horsepower supplied is used. In the first case the Btu supplied per hour = p^?t0r horsepower x 2,546, and Efficiency of motor in the second case Btu per hour = bhp. X 2,546, in which 2,546 is the Btu equivalent of 1 hp-hour. In high-powered mills this is the chief source of heating and is frequently sufficient to overheat the building even in zero weather, thus requiring cooling by ventilation the year round. The heat (in Btu per hour) from electric lamps is obtained by multi plying the watts per lamp by the number of lamps and by 3.415. One cubic foot of producer gas gives off about 150 Btu per hour; one cubic foot of illuminating gas gives off about 535 Btu per hour, and one cubic foot of natural gas gives off about 1000 Btu per hour. A Welsbach burner averages 3 cu ft of gas per hour and a fish tail burner, 5 cu ft per hour. The rate of heat dissipation to the atmosphere by persons depends upon the height and weight of the individuals and state of activity, and for other than moderate temperatures, it varies somewhat with the effective temperature (see Fig. 1, Chapter 28). As an engine for performing mechanical work, the human body is extremely inefficient, and hence the major part of the energy transformation within the body as determined by metabolism is dissipated as heat. Table 2, Chapter 28, gives the metabolic rates at moderate temperatures for an average size man for various degrees of activity in Btu per square foot per hour. This is fche^ total rate of heat dissipation from the body which is divided into sensible v and latent heat.loss in percentages, varying widely with the temperature and humidity of the atmosphere. See Figs. 5, 6 and 7, Chapter 28'. For intermittent heating allow 10 per cent additional for rooms heated . in the day time only, and for longer intervals of several days or more, add 25 per cent in determining minimum heating requirements, and size of plant. EXAMPLES OF HEAT LOSS COMPUTATIONS Factory Building. (See Fig. 1.) 1. Location........................................................................ ......................................Philadelphia, Pa. 2. Lowest outside temperature. (Table3)..................... .......................................-- 6F 3. Base temperature: In this example a design temperature 10 deg F above lowest on record in stead of 15 deg F is used. Hence the base temperature = (- 6 + 10) = + 4 deg F. 4. Direction of prevailing wind (during Dec., Jan., Feb.)........................Northwest 5. Breathing-line temperature (5 ft from floor)........ ...................................... .....60 F 18 Chapter 2--Estimating Heat Losses Fig. 1. Elevation of Factory Building Table 4. Calculation Sheet Showing Method of Estimating Heat Losses of Building Shown in Fig. 1 Part op Building Expo sure Feet Height in Feet Net Surface Area or Crack Length Co effi cient Temp. Diff. Net Btu Exposure Total Factor Btu Brick. H in plaster____ Doors (2 in. Wood).. H in. Crack___ Brick, H in plaster.. Glass. (Single)H in. Crack___ South Wall- 16 N 12 12 N 1 pair doors W W Same as N 120 16 15x4 9 Double Hung Windows (15) See Above 656 144 60 1380 540 0.382 3.34 59.6 57.2 57.2 0.277 1.13 59.6 60.2 60.2 10,820 3.150 11,440 1.15 1.15 Hex 1.15 3,620 6.580 22,800 36.800 45,200 1.15 26,200 1.15 42,400 Hx 1.15 26,000 H* 19,690 East Wall__ Same See as W Above Ha 82,200 Roof, 3 in. Concrete and Slag-surfaced built-up roofing. No Ceiling 0.610 254,000 None 254.000 Floor, 5 in. Stone Concrete On on 3 in. Dirt 50 120 Cinder Concrete. 6000 0.521 15,630 None 15,630 Grand Total of beat required for building in Btu per hour at + 4 deg with 11-mile northwest wind.*_______________________________________________ _____________ 488,780 *Nbtcs.--(1) This building ha9 no partitions and whatever air enters through the cracks on the wind ward side must leave through the cracks on the leeward side. Therefore, only one-half of the total crack will be used in computing infiltration for each side and each end of building. (2) An exposure allowance of 15 per cent is also to be added to the wall and glass transmission losses and to the infiltration losses on the two adjacent sides of the building most nearly facing the prevailing wind ' as stated on page 17. ` (3) It is also possible to compute the heat required to take care of infiltration on the basis of half of an air change per hour as given in Table 3, Chapter 4 for a factory with minimum conditions. Volume -- 50 X 120 X16 = 96,000 cu ft and heat required per hour is 96.000 X H X 0.075 X 0.24 X 59.Q = 51.500 Btu Based on'infiltration through one-half the total crackage in all walls, the heat to be supplied Der hour is from Table.4, 6,580 + 26,000 + 5,720 + 22,600 = 60,900 Btu The value based on crackage should be used, but if building is to be heated intermittently, not less than one air change per hour should be allowed. 19