Document baRXOzpJD6Qaonnn9VZxRBZLg

American Society of Heating and"Ventilating Engineers Guide, 1931 occupancy, may be substituted for a portion of the heating installation. In no case should the actual heating installation (exclusive of heat sources) be reduced below that required to maintain at least 40 deg. fahr. in the building. The allowances indicated in Table 4 may be made when re quired. For more detailed information'see Table 5. Motors and the machinery which they drive, if both are located in the room, convert all of the electrical energy supplied into heat, which is 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 B.t.u. supplied per hour = horsePwer x 2,546, and Efficiency of motor in the second case B.t.u. per hr. = b.hp. X 2,546, in which 2,546 is the B.t.u. 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. 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. (Table 3)___________ ___ _______-- 6 deg. fahr. 3. Base temperature: In this example a design temperature 10 deg. fahr. above lowest on record instead of 15 deg. fahr. is used. Hence the base temperature = (-- 6 + 10) = + 4 deg. fahr. 4. Direction of prevailing wind (during Dec., Jan., Feb.)_____________Northwest 6. Breathing-line temperature (5 ft. from floor) _____ _______________60 deg. fahr. 6. Inside air temperature at roof: The air temperature just below roof is higher than at the breathing line. Height of roof is 16 ft., or it is 16 -- 5 = 11 ft. above breathing line. Allowing 2 per cent per foot above 5 ft., or 2 X 11 =22 per cent, makes the temperature of the air under the roof = 1.22 X 60 = 73.3 deg. fahr. 7. Inside temperature at walls: The air temperature at the mean height of the walls is greater than at the breathing fine. The mean height of the walls is 8 ft. and allowing 2 per cent per foot above 5 ft., the average mean temperature of the walls is'' 1.06 + 60 = 63.6 deg. fahr. By similar assumptions and calculations, the mean temperature of the glass will be found to be 64.2 deg. fahr. and that of the doors 61.2 deg. fahr. 8. Average wind velocity (Table 3)....... ............................... ......... 11.0 miles per hour 9. Overall dimensions (See Fig. 1)............ ................ ______________ 120 x 50 x 16 ft. Chapter 5--Heat Loss Calculations Fig. 1. Elevation of Factory Building -r.,,, _ a Calculation Sheet Showing Method of Estimating Heat Losses of Table ' Building Shown in Fig. 1 Part or Building Expo SURE Width Height in Feet Net Surface Area or Crack Length Co effi cient Temp. Diff. Net B.t.u. Exposure Total Factor B.t.u. Brick. H in. plaster------ Doors (2 in. yiWino. oCdr)a- ck- 50 N 12 12 N 1 pair doors 656 0.277 59.6 10.820 144 0.382 57.2 3.150 60 3.34 57.2 11,440 1.15 1.15 12.460 3.620 6.580 Brick. K in* plaster---- Glass. (Single)- % in. Crack . - W 120 16 W 15x4 9 w Double Hung Windows (15) 1380 540 0.277 59.6 1.13 60.2 22,800 36,800 1.15 1.15 x 1.15 26,200 42,400 26.000 South Wall-- East Wall- Same See as N Above Same See as W Above 19.690 H- 82,200 Roof, 3 in. Concrete and Slag-surfaced built-up roofing. No Ceiling 50 120 0.610 254,000 None 254,000 Floor, 5 in. Stone Concrete On on 3 in. Dirt 50 120 Cinder Concrete. 6000 0.521 None 15.630 Grand Total of heat required for building in B.t.u. per hour at +4 deg. with ll:mile northwest wind____________----------------------------------------------------------------------------------------------------J 488.780 oNotes.--(1) This building has 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 88. (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 59.6 = 51.500 B.t.u. Based on infiltration through one-half the total crackage in all walls, the heat to be supplied per hour is from Table 6, 6,580 + 26,000 + 5.720 + 22,600 = 60,900 B.t.u. 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. 91