Document 5kJyzdxw29z3BNEg3Xxr5K94D

Heating Ventilating Air Conditioning Guide 1939 tures of the various parts of a wall are controlled by the type and amount of insulation used and the vapor densities in the corresponding sections are controlled by the type of vapor barriers installed. The transmission of heat and vapor through a wall should be considered together, and in most cases the proper combination of insulation and vapor barriers will eliminate the possibilities of condensation within walls. A consideration often overlooked in problems of condensation within walls is that a vapor barrier should be placed on the warm side and not on the cold side of a wall. HEAT LOSS COMPUTATION EXAMPLE Fig. 1. Elevation of Factory Building 1. Location----------------------- -------------------- ----------------------------------------- Philadelphia, Pa. 2. Lowest outside temperature. (Table 2)...-- 6F 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)....60 F 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. Insidb 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)i____________________ 11.0 mph 9. jOver-all dimensions (See Fig. 1):______ u_____ .Cl20 x 50 x 16 ft 10. Construction: Walls--12-in. brick, with J-in. plaster applied directly to inside surface. Roof--3-in. stone concrete and built-up roofing. Chapter 7. Heating Load 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 x 4 ft single glass double-hung windows on each side. Transmission coefficients. 11. Walls--(Table 3, Chapter 5, Wall 2B)---------------------------------- M Roof--(Table H, Chapter 5, Roofs 2A and 3A)-------------------- ..U floor_(Table 10, Chapter 5, Floors 5A and 6A)....... ............... ..U Doors--(Table 13B, Chapter 5).................................................. -U Windows--(Table 13A, Chapter 5)............................................. ..U 0.34 0.77 0.63 0.46 1.13 12. Infiltration Coefficients: Windows--Average windows, non-weatherstripped, He-in- .crack and a/ .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 --tati-pn from Chanter 6. 25.0 X 0.018 0.45 Btu per deg Fahrenheit 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 Fahrenheit 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. 13. Calculations: See calculation sheet, Table 3. Table 3. Calculation Sheet Showing Method of Estimating Heat Losses of Building Shown in Fig. 1 Part or Building North Wall: Brick. H-i- plaster------------Doors (2-in. wood)-.......... ...... H in. Crack__________ __ -- West Wall: Brick. W-in. plaster Glass (Single).................. ...... % in. Crack_ . _______ .. South Wnil Kant Wall Roof. 3-in. concrete and slagsurfaced built-up roofing.___ Floor, 5-in. stone concrete on Wa cinder concrete________ Width in Feet Height in Feet Net Sur face Area or Crack Length 50 16 12 12 1 pair doors 656 144 60 120 16 15 x 4 9 Double Hung WindovFS (15) 1380 540 450 Same as North Wall Same as West Wall 50 120 6000 50 120 6000 Coeffi cient 0.34 0.46 0.90 0.34 1.13 0.45 0.77 0.63 Cran'd Total of heat required for building in Btu per hour__ Temp. Difp. . Total Btu 59.6 57.2 57.2 59.6 60.2 60.2 69.2 5b 13,293 3,789 1,544a 27,964 36,734 6,095a 18,626 70,793 319.704 18.000 517,442 This building has no partitions and whatever air enters through the cracks on the windward aide must leave through the cracks on the leeward side. Therefore, only one-half of the total crack will he used in . computing infiltration for each side and each end of building. . bA 5 F temperature differential is commonly assumed to exist between the air on one side of a large hoot laid on the ground and the ground. 141