Document YGXwpKkRZGam5DORQkmaOjz6O

American Society of Heating and Ventilating Engineers Guide, 1935^ b. At a floor 150 ft above the ground M, = VW~- 175 X 60 = 11.0 mph 10 A room contains three 2 ft-8 in. by 5 ft-6 in. plain double-hung wood w' dows with Jfg-in. crack and %4-in. clearance. Assume a wind velocity^ 20 mph and a temperature difference of 75 F. Neglecting chimney effect, is the maximum heat loss due to infiltration? 0,1 From Table 2, heat loss per foot of crack per degree temperature difference is l.i per hour. Length of crack for the three windows is 57 ft. The maximum heat loss d? to infiltration, is equal to 1.067 X 57 X 75 or 4561 Btu per hour. '. 11 Find the infiltration through a wall with 16-in. shingles on 1 in. by.4;. boards with 20 mph wind velocity. Give the pressure drop through the wall -Referring to Curve 3C,-Fig..l,.the value on-the horizontal scale corresponding-to 20 mi is approximately 102 cfh per square foot of wall. - The pressure drop through the wall is 0.193 in. of water (see left hand vertical scale) 12 t What will be the infiltration through air-dried end and side-matched sheathing for 15 mph wind velocity? Referring to Curve 10C, Fig. 2, the value on the horizontal scale corresponding 15 mph is 50 cfh per square foot of wall. 13 From Table 2, find the infiltration (cubic feet per hour per foot of crack] for an average double-hung window, not weather stripped, with a 20 mpl wind velocity. 59.3 cu ft per foot of crack per hour. 14 Using the value found in Question 11, what will be the heat requirement in a building with a total crack (all windows and doors) of 180 ft if the wind velocity is 15 mph, the outside temperature is 0 F, and the inside temperatun is 70 F? Using one half of the total crack, the volume of air is: 90 X 59.3 = 5337 cu ft H = 0.018 X 5337 X (70 - 0) = 6724.6 Btu. (See Equation 4.) 130 Chapter 7 HEATING LOAD V .^^ CovernineHeat Demand, Procedure, Temperatures, Movement, Heat Sources Other Than Heating Plant, wina Frumnle. Condensation TO design any system of heating, the maximum probable heat demand must be accurately estimated in order that the apparatus installed hall be capable of maintaining the desired temperature at all times. .The factors which govern this maximum heat demand--most of which are seldom if ever, in equilibrium--include the following: 1. Outside temperature. 2. Rain or snow. 3. Sunshine or cloudiness. 4. Wind velocity. 5. Heat transmission of exposed parts of building. 6. Infiltration of air through cracks, crevices and open doors and windows. 7. Heat capacity of materials. 8. Rate of absorption of solar radiation by exposed materials. 9. Inside temperatures. 10. Stratification of air. 11. Type of heating system. 12,. Ventilation requirements. 13. Period and nature of occupancy. . 14. Temperature regulation. Outside Conditions 1 (The Weather) Building Construction Inside Conditions The inside conditions vary from time to time, the physical properties of the building construction may change with age, and the outside conditions are changing constantly. Just what the worst combination of all of these variable factors is likely to be in i.any particular case is therefore con jectural. Because of the nature of the problem, extreme precision. in estimating heat losses at any time, while desirable, is hard of attainment. The procedure to be followed "in determining the heat loss from any building can be divided into, seven, consecutive steps, as follows: 1. Determine on the inside air temperature, at the breathing line or the 30-in.;line, which is to be maintained in the building during the coldest weather. (See Table 1.)' ' ( 2. Determine on an outside air temperature for design purposes, based on the: minimum temperatures recorded in the locality in question, which will provide for all but the most severe weather conditions. Such conditions as may exist for only a few_ consecutwe_hours are readily taken care of by the heat capacity of the building itself. 131