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Heating Ventilating Air Conditioning Guide 1939 Heating Load 3. 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 5.) '1 4. Measure up 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. 5. 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 and 2.) but inasmuch as the heating system proportioned for taking care T'/he heat losses will usually have a capacity about 100 per cent greater h n that required for average winter weather, and inasmuch as most h ^ldings may either be continuously heated or have more time allowed f U1 heating-up during the few minimum temperature days, no allowance is made except in the size of boilers or furnaces. INSIDE TEMPERATURES 6. 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 6.) The inside air temperature which must be maintained within a building and which should always be stated in the heating specifications is underr stood to be the dry-bulb temperature at the breathing line, 5 ft above the floor or the 30-in. line, and not less than 3 ft from the outside walls. 7. The sum of the heat losses by transmission (Item 5) through the outside wall and glass, as well as through any cold floors, ceilings or roof, plus the heat equivalent (Item 6) of the cold air entering by infiltration represents the total heat loss equivalent for any building. Item 7 represents the heat losses after the building is heated and under ; stable operating conditions in coldest weather. Additional heat is ? required for raising the temperature of the air, the building materials and I the material contents of the building to the specified standard inside j ftemperature. The rate at which this additional heat is required depends upon the { heat capacity of the structure and its material contents and upon the time in which these are to be heated. j Inside air temperatures, usually specified, vary in accordance with the use to which the building is to be put and Table 1 presents values which con form with good practice. The proper dry-bulb temperature to be maintained depends upon the relative humidity and air motion, as explained in Chapter 3. In other words, a person may feel warm or cool at the same dry-bulb temperature, depending on the relative humidity and air motion. The optimum winter effective temperature for sedentary persons, as determined at the A.S.H. V.E. Research Laboratory, is 66 deg.1 According to Fig. 6, Chapter 3, for so-called still air conditions, a relative humidity of approximately 50 per cent is required to produce an effective temperature of 66 deg when the dry-bulb temperature is 70 F. This additional heat may be figured and allowed for as conditions re- Table 1. Winter Inside Dry-Bulb Temperatures Usually Specified* i However, even where provision is made for artificial humidification,, the relative humidity is seldom maintained higher than 40 per cent during the extremely cold weather, and where no provision is made for humidifica tion, the relative humidity may be 20 per cent or less. Consequently, in using the figures listed in Table 1, consideration should be given to 1 Ttpi or Building DsoFahb Trre or Buildino Deo Fahb whether provision is to be made for humidification, and if so, the actual I relative humidity to be maintained. ! Schools Theaters-- 1 Temperature at Proper Level: In making the actual heat-loss compu i I Assembly rooms......................... Toilets and baths_____________ Wardrobe and locker rooms___ 70-72 68-72 55-65 70 65-68 Hotels-- 66\ 68-72 68-72 68 '$ -d 70 tations, however, for the various rooms in a building it is often necessary to modify the temperatures given in Table 1 so that the air temperature at the proper level will be used. By air temperature at the proper level is meant, in the case of walls, the air temperature at the mean height be tween floor and ceiling; in the case of glass, the air temperature at the 65-76 Playrooms........................... 60-65 Natatoriums.- ........................... 75 70 . Kitchens and laundries_________ 66 Ballrooms................. ....................... 65-68 Toilets and service rooms............. 68 5 n mean height of the glass; in the case of roof or ceiling, the air temperature at the mean height of the roof or ceiling above the floor of the heated room;and in the case of floors, the air temperature at the floor level. In Hospitals-- Private rooms.............. ,,........... Private rooms (surgical). -.... 70-72 70-80 70-95 68 66 Homes Stores PiTRi.ir RiTTi.niNns Steam ratws 70-72 65-68 68-72 120 110 5!1 II: the case of heated spaces adjacent to unheated spaces, it will usually be sufficient to assume the temperature in such spaces as the mean between the temperature of the inside heated spaces and the outside air tempera ture, excepting where the combined heat transmission coefficient of the roof and ceiling can be used, in which case the usual inside and outside 68 70-80 Foundries and boiler shops... Paint shops. 60-65 50-60 80 temperatures should be applied. (See discussion regarding the use of combined coefficients of pitched roofs, unheated attics and top-floor ceilings Chapter 5.) "The most comfortable dry-bulb temperature to be maintained depends on the relative humidity and air motion. These three factors considered together constitute what is termed the effective temperature. (See Chapter 3). 132 *See Chapter 3, p. 61. 133