Document QE6BBo1xwGNkvN9Evzpgxo86

American Society of Heating and Ventilating Engineers Guide, 1930 Economic Value of Weatherstripping Tables 39 and 40 show the heat losses in B.t.u. per hour per foot of crack for plain windows and weatherstripped windows to heat the incoming air from 0 to 70 deg. fahr. The tables also show the radiation in square feet that must be installed to take care of these heat losses. This radiation is based on a heat emission factor of 240 B.t.u. per square foot. For example, consider a double-hung window at a wind velocity of 15 miles per hour. For a plain non-stripped window, Table 39 shows that 0.65 sq. ft. of radiation is required to take care of the infiltration loss per foot of crack. This table shows for the weatherstripped window, a cor responding radiation requirement of 0.12 sq. ft. per foot of crack, indi cating that the application of good weatherstripping has brought about a reduction of 0.53 sq. ft. in the radiation required per foot of crack. Assuming the heating system costs $2.00 per square foot of radiation installed, and weatherstripping to cost $0.30 per lineal foot installed, there would result for each $0.30 invested in weatherstripping, a reduction of $1.06 in the initial cost of the heating system. For any particular instal lation the costs applying to that locality and for that particular type of construction should be used in making such a cost analysis. No attempt is made here to figure the reduction in operating cost due to the applica tion of weatherstripping, as this varies greatly depending on how tlie plant is operated. WIND MOVEMENT The effect of wind on the heating requirements of any building should be given consideration under two heads: 1. Wind movement increases the heat transmission of walls, glass, and roof, affecting poor walls to a much greater extent than good'walls. 2. Wind movement materially increases the infiltration (inleakage) of cold air through the cracks around doors and windows, and even through the building materials them selves, if such materials are at all porous. It is entirely possible that a building may require more heat on a windy day with a moderately low outside temperature than on a quiet day with a much lower outside temperature. It will, therefore, be evident that the wind movement in any locality must be given careful consideration in computing the probable heating requirements of a building, and for the purposes of calculation, not less than the average wind movement in any locality during December, January and February should always be pro vided for in computing (1) the heat transmission of a building, and (2) the heat required to take care of the infiltration of outside air. The first condition is readily taken care of, as already explained, by using a surface coefficient f0 for the outside wall surface which is based on the proper wind velocity (Table 5). In case specific data, are lacking for any locality, use an average wind velocity of approximately 15 miles per hour- In a similar manner, the heat allowance for infiltration through cracks (Tables 39 to 42), must be based on the average wind velocity for a given locality, and is explained in the next subdivision of this chapter. , 70 T able 40. I nfiltration through Double-Hung M etal Sash Windows per Foot of Crack Chapter 2--Heat Losses from Buildings 71