Document kmnqQE1Zzo8GKLexRyBYxy4qO

American Society of Heating and Ventilating Engineers Guide, 1935 EXAMPLE OF HEAT LOSS COMPUTATIONS Fig. 1. Elevation of Factory Building 1. Location..... ......................................... ................................................ Philadelphia, Pj_ 2. Lowest outside; temperature. (Table2).......................................................... _gp` 3. Base temperature: In this example a design temperature 10 F above lowest on record instead of 15 F is used. Hence the base temperature = (- 6 + 10) = + 4 F. 4. Direction of prevailing wind (during Dec., Jan., Feb.)..... ........ ........Northwest: 5. Breathing-line temperature (5 ft from floor)..............;.................................. 60fj 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 tem perature of the air under the roof = 1.22 X 60 = 73.2 F. 7. Inside temperature at walls: The air temperature at the mean height of the walls is greater than at the breathing line. 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 X 60 = 63.6 F. By similar assumptions and calculations, the mean . temperature of the glass will be found to be 64.2 F and that of the doors 61.2 F. 8. Average wind velocity (Table, 2).................................. ........................... lLO mph j 9. Over-all dimensions (See Fig. 1)........................................................120 x 50 x i6 ft | 10. Construction: Walls--12-in. brick, with J4-in. plaster applied directly to inside surface. Roof--3-in. stone concrete and built-up roofing. . Floor--5-in. stone concrete on 3-in. cinder concrete on dirt. Doors--One 12 ft x 12 ft wood door (2 in. thick) at each end. Windows--Fifteen, 9 ft x4 ft single glass double-hung windows on each side 11. Transmission coefficients: Walls--(Table 3, Chapter 5, Wall 2B)................ ...................... . U - .0.34 Roof--(Table 11, Chapter 5, Roofs 2A and 3A)_.......-.... ____ - U -- 0,77 Floor--(Table 10, Chapter 5, Floors 5A and 6A)................... . U =. 0.63 Doors--(Table 13B, Chapter 5)._.......................... ............ . U = 0.46 Windows--(Table 13A, Chapter 5)..... C................ 1...... 7 = 1.13 Infiltration Coefficients : 12. Windows--Average windows, non-weatherstripped, >f6-in. crack and %4-in. clearance. The leakage per foot of crack for an 11-mile wind velocity is 25.0 cfh. (Determined by interpolation of Table 2, Chapter. 6.) The heat equivalent per hour per degree per foot of crack is taken from Chapter 6. 25.0 X 0.018 = 0.45 Btu per deg Fahr per foot of crack. Doors--Assume infiltration loss through door crack twice that of windows or 2 X 0.45 = 0.90 Btu per deg Fahr per foot of crack. Walls--As shown by Table 1, Chapter 6, a plastered wall allows so little infiltration that in this problem it may be neglected. Calculations: See calculation sheet, Table 3. 13 Table 3. Calculation Sheet Showing Method of Estimating Heat Losses of Building Shown in Fig.. 1 Part of Doors (2-in. wood) . K la. Ctf -' West Wall: , . Brick. X-"! f>la3ler Glass (Single).. # in. Crack. Width in Feet Height IN Feet Net Sur face Area or Crack Length Coeffi cient 5102 II }1S2 1 pair doors 120 15x4 | Double Hung Windows (15) 656 144 60 1380 540 0.34 0.46 0.90 0.34 1.13 0.45 Temp. Diff. 59.6 57.2 57.2 59.6 60.2 60.2 Total Btu 13,293 3.789 1,544* 27.964 36.734 6.095* 18,626 70.793 Roof, 8-m. concrete and slag-. surfaced built-up roofing--.__1 Floor, 5-tn. stone concrete on 3-in, dnder concrete.^__ .... 6000 Grand Total of heat required for building in Btu per hour- 0.63 319.704 18,900 517,442 This building has ho partitions and whatever air enters through the cracks bn the windward side must . leave through the cracks on the leeward side. Therefore, only one-half of the total crack will be used in cotnpaUag infiltration for each side and each end of building. . VA 6 F temperatiire differential is commonly assumed to exist between the air on one side of a large, floor laid on the ground and the'ground. ' PROBLEMS IN PRACTICE V t The dry-bulb temperature and the relative humidity at the ceiling of a mixing room in a bakery are 80 F and 60 per cent, respectively. The roof is a 4-in. concrete deck covered with built-up roofing. If the lowest outside tem perature to be expected is --10 F, what thickness of rigid fiber insulation will be required to prevent condensation? From Table 11, Chapter 5, U for the uninsulated roof = 0.72. From Table 2, Chapter 5, k for rigid fiber insulation = 0.33. From the psychrometric chart, Chapter 1, the dew point of air at 80 F and 60 per cent relative humidity is 65 F. The ceiling temperature, therefore, must not drop below 65 F if condensation is to be prevented.