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! |American Society of Heating and Ventilating Engineers Guide 935 Chapter 8--Cooling Load transmission through the glass caused by the difference betweer/J temperatures of the inside and outside air. Another reason for neg'- - this glass transmission load is that the curves in Fig. 1 were based on A3 maximum intensity of solar radiation observed at the A.S.H.V.E. Labi; tory during a three-year study, so results based on these curves wilu amply high. It will be noted that Table 4 gives the amount of J delivered through the window as 97 pier cent of the solar radiation, Jy is greater than is indicated by the figures for absorption, in the --' ^ paragraph. The explanation is that much of the radiation absorbent the glass is delivered to the.room. ? f air entering due to infiltration may be estimated from data The volume o j information on the amount of outside air required fven '"Sfon will be found in Chapter 2. for venu dtine from the outside air introduced may be esti- tom _ qj, m,, - e> (2) vhere . removed from outside air entering the building, Btu per hour. Bi ~ hef\7 f outside air entering the building, cubic feet per hour. = density of outside air, pounds of dry air per cubic foot of outside air, at the Fig. 1 shows that the maximum solar intensity on any surface limited duration. In the case of 'windows the total energy impinging . - heatcontent of mixture of outside dry air (at temperature to) and water vapor, the glass before and after the time of maximum intensity is fu^g heat tent0ofmbeture of inside dry air (at temperature t) and water vapor, reduced by increased shading of the glass from the frame, or wall, ft BUi per pound of dry air. cooling load due to solar radiation therefore does not have to be figuredj a steady load. Another point which should be noted is that the maxim solar radiation load on an east wall occurs early in the morning whenti outside temperature is low. | In a recent paper by the A.S.H.V.E. Research Laboratory7 it was sho| Heat and Moisture Sources F 6 to 9 Chapter 2, show the heat and moisture given off by human . invs under yarious conditions of activity. For average conditions where aMRon is normally at rest, as in a theater, or doing very light work, as in a restaurant or residence, the total amount of heat given off will average that ordinary double strength window glass transmits no measurafi | about 400 Btu per hour. Part of this is latent heat due to the evaporation amount of energy radiated from a source at 500 F or lower; that it trail I of,700 to 1200 grains of moisture per hour. Examples illustrating heat and mits only 6.0 and 12.3 per cent, of the total radiation from surfacesa moisture loss calculations for human beings are given in Chapter 2. 700 F and 1000 F, respectively; and that it transmits 65.7 per cent of ^ radiation from an arc lamp, 76.3 per cent of the radiation from an Table 5. Heat Gain Due to Various Devices, Btu per Hour candescent tungsten lamp, and 89.9 per cent of the radiation from tii sun. Thus, glass windows in a room constitute heat traps, which all rather free transmission of radiant energy into the room from the sunl Lights and electric appliances.-................ Motors, Ho hp....................... .................... Motors, 1 hp...........................~.................. warm objects in it, but do not allow the transmission of re-radiated ho Restaurant coffee urns, 10-gal capacity.. from these same objects. | & Dish warmers per 10 sq ft of shelf........... Restaurant range--4 burners and oven.. 3,415 per kilowatt 255 2,546 16,000 6,000 100,000 Some recent tests4 indicated that sunshine through window glass! g Residence gas range the most important factor to contend with in the cooling of an qf5g Giant burner..........................................- 12,000 building. At times it was shown to account for as much as 75 per cent'# IJ .. Medium burner................................. .-- the total cooling necessary. Because of the importance of the sunshiS ^ Ovext........................................................ 'Pilot- 9.000 1.000 per cu ft of space 250 load, cooling systems should be zoned so that the side of the building Electric Range which the sun is shining can be controlled separately from the other sida ;j|Sihall burner, 100 to 1350 watts.-- 3,415 to 4,600 of the building. If buildings are provided with awnings so that (8 window glass is shielded from sunshine, the amount of cooling require! -jgllaige burner, 1700 to 2200 watts... jXClven, 2000 to 3000 watts.......... ...... `"' Appliance connection, 660 watts..... 5,800 to 7,500 6,830 to 10,245 2,250 will be reduced and there will also be less difference in the cooling requins 'jj Warming compartment, 300 Watts- 1,025 ments of different sides of the building. The total cooling load foijj g building exposed to the sun on more than one side is of. course less dm jg* ----AJj spurces of heat must of course be considered in designing the con the sum of the maximum cooling loads in the individual rooms since | f ditioning system. The heat gain due to various devices is given in maximum solar radiation load on the different sides occurs at diffei Table 5. An example of cooling load calculation is given in Chapter 9. times. Heat and Moisture Leakage An allowance must be made for the heat and moisture in the outsideg introduced for ventilating purposes or entering the building th cracks, crevices, doors, and other places where infiltration might occl 'Radiation of Energy Through Glass, byj. L. Blackshaw and F. C. Houghten (A.S.H.V.E. JoS Section, Heating, Piping and Air Conditioning, October, 1933). PROBLEMS IN PRACTICE . 4 a*j'*What should be the dry- and wet-bulb temperatures in a restaurant f' *"*ti.the outdoor dry-bulb temperature is 95 F? ; AFhat is the most desirable indoor dry-bulb temperature and relative mnnidity in an office building in summer? - ^'bulb' 80 F; wet-bulb, 65 F- (Table 2, Chapter 2.) , *^76.5 IJ-and 50 per cent relative humidity. (Fig. 3, Chapter 2.) 152