Document 2JByye72r0kqzna3RxkvX13Ep

HEATING VENTILATING AIR CONDITIONING CUIDE 1943 pancy, may be substituted for a portion of the heating installation. In no case should the actual heating installation (exclusive of heat sources) be reduced below that required to maintain at least 40 F in the building. Electric Motors and Machinery Motors and the machinery which they drive, if both are located in the room, convert all of the electrical energy supplied into heat, which is retained in the room if the product being manufactured is not removed until its temperature is the same as the room temperature. If power is transmitted to the machinery from the outside, then only the heat equivalent of the brake horsepower supplied is used. In the first case the Btu supplied per hour = Motor horsepower ^ 2546, and Efficiency of motor in the second case Btu per hour = bhp X 2546, in which 2546 is the Btu equivalent of 1 hp-hr. In. some mills this is the chief source of heating and it is frequently sufficient to overheat the building even in zero weather, thus requiring cooling by ventilation the year round' The heat (in Btu per hour) from electric lampis is obtained by multi plying the watts per lamp by the number of lamps and by 3.413. One cubic foot of producer gas gives off about 150 Btu per hour; one,cubic foot of illuminating gas about 535 Btu per hour; and one cubic foot of natural gas about 1000 Btu per hour. A Welsbach burner averages 3 cu ft of gas per hour and a fish-tail burner, 5 cu ft per hour. For information concerning the heat supplied by persons, refer to data given in Chapter 2. GENERAL PROCEDURE The eight steps required for calculating heat losses of a structure are. 1. Determine on an outside air temperature for design purposes, based on the mini mum temperatures recorded in the locality in question, which will provide for alt but the most severe weather conditions. Such conditions as may exist for only a few consecu tive hours are readily taken care of by the heat capacity of the building itself.- (See Fig. 1). 2. 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). 3. Estimate temperatures in adjacent unheated spaces and the attic. The attic temperature need not be estimated if the combined roof and ceiling coefficient is used. 4. Select or compute the heat transmission coefficients for outside walls and glass; also for inside walls, floors, or top-floor ceilings, if these are next to unheated space; include roof if next to heated space. (See Chapter 4). 5. Measure amount of net outside wall, glass and roof next to heated spaces, as well, as any cold walls, floors or ceilings next to unheated space. Such measurements are made from building plans, or from the actual building, using inside dimensions. 6. Compute the heat transmission losses for each kind of wall, glass, floor, ceiling and roof in the building by. multiplying the heat transmission coefficient in each case by the area of the surface in square feet and the temperature difference between the inside and outside air. (See Items 1, 2, and 3). . 7. Select unit values and compute the heat equivalent of the infiltration of cold air taking place around outside doors and windows. These unit values depend on the kind or width of crack and wind velocity, and when multiplied by the length of crack and the temperature difference between the inside and outside air, the result expresses the heat required to warm up the cold air leaking into the building per hour. (See Chapter 5). 140 CHAPTER 6. HEATINC LOAD 8. The sum of the heat losses by transmission (Item 6) through the outside wall and glass, as well as through any cold floors, ceilings or roof, plus the heat equivalent (Item 7) of the cold air entering by infiltration represents the total heat loss equivalent for any building. INTERMITTENTLY HEATED BUILDINGS Item 8 represents the heat losses after the building is heated and under stable operating conditions in coldest weather. In the case of intermit tently heated buildings additional heat is required for raising the tem perature of the air, the building materials and the material contents of the building to the specified inside temperature. The rate at which this additional heat must be supplied depends upon the heat capacity of the structure and its material contents and upon the time in which these are to be heated5. This additional heat may be figured and allowed for as conditions re quire, but inasmuch as the heating system proportioned for taking care of the heat losses will usually have a capacity about 100 per cent greater than that required for average winter weather, and inasmuch as most buildings may either be continuously heated or have more time allowed for heating-up during the few minimum temperature days, no allowance is usually made except in the size of boilers or furnaces. For churches, auditoriums and.other intermittently heated buildings, additional capacity should be provided. RESIDENCE HEAT LOSS PROBLEMS Example S. Calculate the heat loss of residence shown in Fig. 2 located in the vicinity of Chicago. Assume inside and outside design temperatures to be 70 F and --10 F respectively. The attic is unheated. Assume ground temperature to'be 50 F under basement and garage floors and 32 F adjoining basement walls. Estimate in filtration by crack method, assuming average wind velocity to be 12.5 mph during December, January.and February. No wall, ceiling or roof insulation is to be figured in this problem, but all first and,second floor windows are to have storm sash. The building is constructed as follows (transmission coefficients (U) in parentheses): Walls: Brick veneer, building paper, wood sheathing, studding, metal lath and plaster (0.28). Walls of dormer over garage, same except wood siding in place of brick veneer (0.26). Attic Walls: Brick veneer, building paper, wood sheathing on studding (0.42). Basement Walls: 10 in. concrete (0.10). Roof: Asphalt shingles on wood sheathing on rafters (0.56). Ceiling (Second floor): Metal lath and plaster (0.69). Windows: Double-hung wood windows with storm sash (0.45). Steel casement sash in basement (1.13). Floor (Bedroom D): Maple finish flooring on yellow pine sub-flooring; metal lath and plaster ceiling below (0.25). Floor (Basement and Garage): 4 in. stone concrete on 3 in. cinder concrete (0.10). Solution: The calculations for this problem are given in Table 3, and a summary of the results in Table 4. The values in column F of Table 3 were obtained by multiplying together the figures in columns C, D and E. The heat losses are calculated to the nearest 10 Btu. See reference notes for Table 3 for further explanation of data. Attention is called to the summary of heat losses (Table 4) of the uninsulated residence (Fig. 2). As storm windows are usexl in this instance the glass and door trans- *Heat Requirement Tables for Intermittently Heated Buildings, (Engineering Experiment Station Bulletin, No. 450, A. and M. College of Texas, College Station, Texas), contains a set of tables applicable to either intermittent heating or cooling. ' Further information may be found in a paper, A Method of Com piling Tables for Intermittent Heating, by Elmer G. Smith (A.S.H.V.E. Journal Section, Heating, Piping and Air Conditioning, June. 1942, p. 386). 141