Document qVJZyXV102DJOkEVmEY4nQvM

American Society of Heating and Ventilating Engineers Guide, 1932 t? 50.03 u a Q$ ae Q7 A1 bt c d 1 a 1 r t t j /1 1 7 ( n i 7f 7 1/ tf j7 / 7t L1 A-V I I _ 1 ! / 77 / / f RmSrnpM Sash Suspended Q5 t> 7 Q4 03 j/ ! / U / k h/ 0? 7 T 7V V/ O' Same As C With Wool _Wamex-SreiP Appueo _ I a/ / j Mr- 0 so too Infiltration CF.HPcji Foot Of Crack Fig. 6. Infiltration through Sash Perimeter of Window, with and without Storm Sash--in. Crack and >62 in. Clearance AIR CHANGE METHOD OF ESTIMATING INFILTRATION The amount of air leakage is sometimes roughly estimated by assuming a certain number of air changes per hour for each room, the number of cha'nges assumed being dependent upon the type, vise and location of the room, as indicated in Table 3. Fig. 7. Infiltration through Sash Perimeter of Window with and without Storm Sash--% in. Crack and A in. Clearance 78 Chapter 4--Air Leakage from Buildings HEAT REQUIRED TO WARM AIR ENTERING BY INFILTRATION Because of the influx of cold air by infiltration, provision must be made for the heat required to warm this air to room temperature. The heat required is given by the following equation: where Hi = 0.24 Q d (l -- t,,) (3) H\ = Btu per hour required for heating air leaking into building from outside temperature l0 to inside temperature, t. Q = cubic feet of air entering per hour at inside temperature, t. d -- density (pounds per cubic foot) of air at inside temperature, t. t = inside temperature at the proper level. to -- outside air temperature for which heating system is designed. 0.24 = specific heat of air. X Fig. 8. Diagram Showing Part of Perimeter of Building (in heavy outline) for Which Allowance Should be Made on Account of Exposure to Prevailing Winds It is sufficiently accurate to take d = 0.075 lb in which case the equa tion reduces to Hi = 0.018 Q{t - t0) (4) While a heating reserve must, be provided to warm inleaking air on the windward side of a building, this does not necessarily mean that the heating plant must be provided with areserve capacity, since the inleaking air, warmed at once by adequate heating surface in exposed rooms, will move transversely and upwardly through the building, thus relieving other radiators of a part of their load. The actual loss of heat of a building caused by infiltration is not. to be confused with the necessity for pro viding additional heating capacity for a given space. Infiltration is a disturbing factor in the heating of a building, and its maximum effect (maximum in the sense of an average of wind velocity peaks during the heating season, above some reasonably chosen minimum) must be met by a properly distributed reserve of heating capacity, which reserve, how ever, is not in use at all places at the same time, nor in any one place at all times. Example. Consider a room with four 7 ft x 4. ft;double-hung weatherstripped wood windows with A in. crack, and calked frame. Assume a wind velocity of 20 mph and a temperature difference of 70 F. Neglecting chimney effect, what is the maximum heat loss of this room due to infiltration? 79