Document 3oj6XVgBLNjb44NzOzb3NENE

146 - Chapter 7 1945 Guide In Equation 2, / = 1 for 6are windows because the tests from which Table 7- was obtained showed that approximately all of the solar radiation impinging on a bare window became a part of the heat load in the room. This was because almpst all of the heat absorbed by the glass flowed into the room by conduction.- Other tests10 have indicated that in the case of a building having floors of high heat capacity such as concrete floors on which the solar radiation falls, some of the heat entering a bare window is absorbed by the floor and does not immediately become a part of the cooling load, but is delivered back to the air in the building at a slow rate. The maximum solar intensity on any surface is of limited duration as shown in Fig. 1. In the case of windows the total energy impinging on the glass before and after the time of maximum intensity is further reduced Table 8. Heat Gain Through Glass Blocks3 Solas Radiation Heat Gain (Disect plus Sky) Btu per Sq Ft per Hour Side Easto Westc N. Latitude Degrees 40 40 30 South 35 40 Total Heat Gain 5 (Solar Radiation plus Normal Transmission) Btu per Sq Ft per Hour Easto Westc South 45 40 40 30 35 40 45 San Outside Time TempF 7KX> 74 65.0 8:00 76 63.0 9:00 79 40.0 10:00 83 24.0 11:00 87 15.5 12:00 90 10.0 1.-00 93 7.0 2:00 3:00 4:00 94 95 95 6.0 5.0 4.5 5:00 6:00 7:00 93 91 89 4.0 2.5 1.5 0.0 5.0 6.0 7.0 10.0 15.5 24.0 40.0 65.0 63.0 23.5 0.0 1.0 3.0 5.5 8.5 12.0 14.0 12.0 8.5 5.5 3.0 1.0 0.0 2.8 4.4 7.1 11.3 15.2 17.4 15.2 11.3 7.1 4.4 2.8 0.7 3.0 6.5 10.2 14.7 18.7 21.0 18.7 14.7 10.2 6.5 3.0 0.7 0.0 5.0 11.0 13.4 17.1 21.8 24.8 21.8 17.1 .13.4 11.0 5.0 3:0 0.7 61.0 77.5 73.5 57.5 45.0 36.5 30.0 24.0 19.5 15.5 12.5 10.5 8.0 --4.5 -2.0 0.0 2.0 5.0 5.0 7.0 6.5 11.0 15.0 7.5 10.5 22.0 16.5 21.5 25.0 22.0 28.0 31.8 35.0 55.0 77.0 26.0 24.0 20.0 32.0 29.8 25.5 85.5 55.0 18.5 15.0 9.5 3.5 20.0 13.5 7.0 -0.5 4.0 10.0 .18.0 25.5 33.8 38.5 39.0 36.5 31.5 25.2 18.0 11.0 1.0 5.0 12.0 20.8 .32.0 40.8 46.0 47.0 45.0 40.5 33.5 25.5 18.0 *For August 1. b Inside temperature, 78 F. cFor east and west walls th&e values can be applied to all latitudes between 30 and 45 deg N without . excessive errors. by increased shading of the glass from the frame, or wall. The cooling load due to solar radiation therefore does not have to be calculated as a steady load. Another point which should be noted is that the maximum solar radiation load on the east wall occurs early in the morning when the outside temperature is low. Tests have been made which indicate that solar radiation through window glass is the most important factor to contend with in the cooling of an office building. At times it was shown to account for as rriuch as 75 per cent of the total internal sensible cooling necessary. Because of the importance of the sun load, cooling systems should be zoned so that the side of the building on which the sun is shining can be controlled separately from the other sides of the building. If buildings are provided with awnings so that the window glass is shielded, from sunshine, the WA.S.H.V.E. Research Report No. 1002--Cooling Requirements of Single Rooms in a Modern Office Building, by F. C. Houghten, Cart Gutberlet, and Albert J. Wabl (A.S.H.V.E. Transactions Vol 41. 1935, p. 53). Cooling Load ' 147 amount of cooling required will be reduced and there will also be less difference in the cooling requirements of different sides of the building., The total cooling load for a building exposed to the sun on more than one side is of course less than the sum of the maximum cooling loads in the individual rooms since the maximum solar radiation load on the different sides occurs at different times. In determining the total cooling load for a building if the time when the maximum load occurs is not obvious, the load should be calculated for various times of day to determine the times at which the sum of the loads on the different sides of the building is a maximum. The direct solar and scattered sky radiation penetration through glass block panels is given in Table 8 for various times of the day for south, east and west exposures for different latitudes on August 1'. This table also gives the total heat gain into an air conditioned space when 78 F is maintained indoors, resulting from the effect of both radiation and air to air transmission. These values result from A.S.H.V.E. Laboratory data11 and apply for expected design radiation intensity, and for a design day having a maximum temperature of 95 F. The resulting heat gains are averages for four typical glass block designs, two having smooth exterior faces, and the other two having exterior ribbed faces. Heat Emission of Occupants The heat and moisture given off by human beings under different states of activity are shown in various tables and figures of Chapter 2 which _ covers the physical and physiological principles of air conditioning. It will be observed from these data that the rate of sensible and latent heat emission by human beings varies greatly depending upon state of activity. In many applications this component becomes a large per centage of total load. Metabolic rates are markedly variable for some extreme environmental conditions and this is another important factor which must be considered in cooling load computations. Heat Introduced by Outside Air An allowance must be made for the heat and moisture in the outside air introduced for ventilation purposes and entering the building through cracks, doors, and other places where infiltration might occur. The volume of air entering due to infiltration may be estimated from data given in Chapters 5 and 6. Information on the amount of outside air required for ventilation will be found in Chapter 2. The possible peak load caused by infiltration and ventilation require ments must be carefully considered. In general, as the ventilation in creases the infiltration will tend to decrease. The external pressure on the windward side of the building is often greater than the pressure within and under this condition there will still be infiltration even with large ventilation quantities. Frequently this does not appreciably affect the refrigeration calculation as infiltration can usually be compensated for by decreasing ventilation. Infiltration, however, does affect the required apparatus dew-point, particularly in rooms of one exposure. The heat gain resulting from outside air introduced may be determined by Equation 3: H = -^-(Ao-Ai) (3) llLoc. Cit. Note 1.