Document dDmObkmp7V6eKgg0GDBDp63n6

320 CHAPTER 13 1957 Guide the same that a single table suffices. Note, however, that corrections must be made for certain hours for east and west facing walls of some patterns. Example 10: Find the total instantaneous heat gain through an east wall of 8-in. hollow glass block of Type V pattern at 8 a.m. and 50 deg north latitude. The design temperatures are 80 F indoors and 95 F maximum outdoor dry-bulb, clear atmosphere. Solution: The gain due to transmitted solar radiation is found from Table 20 for Type I pattern. The factor for Type V is found from Table 22. The convection and radiation gain is found from Table 21 (note the footnote). The total instantaneous heat gain is, from Equation 2a, q = 86 X 0.65 + 26 X 1.4 = 92.3 Btu per (hr)(sq ft). Effect of Deviations from Design Conditions If the indoor temperature differs from 80 F, or the design outdoor drybulb temperature differs from 95 F, corrections can be made to the convec tion and radiation gain values for flat glass, rolled figured glass, and glass block according to the schedule in Table 23. The effect of the humid industrial type atmosphere is to cause a con siderable reduction in heat gain, if all factors except solar intensity remain the same. Reference 22 gives heat gain values for four orientations at 40 deg north latitude on August 1 for several types of flat glass and glass block, and solar intensities typical of humid industrial atmospheres. These data show that the following approximate reductions, based on total gain for the day, can be expected: 20 percent for all types of glass and glass block in east or west facing walls; 10 percent for south facing flat glass; 5 percent for south facing glass block walls. Shading of Glass Areas--Design Tables The effects and possibilities of shading should be carefully investigated whenever the heat gain from glass is a large portion of the cooling load. Vertical glass, which is not mounted in the plane of the building surface, is partially shaded by the setback. If a vertical window of. height l and width w be set back from the plane of the building a distance s, the fraction of the total area of the window which receives direct solar radiation is: where n tan 0 nr, tan 0 tan y G, = 1 ------------- r, tan y H------------------------- cos y cos y (5) n = e/I, r, = s/w, 0 = solar altitude, and y is the wall solar azimuth (see Fig. l)- Values of /S and y for various latitudes and August I are given in Table;/ - 6. Special cases not covered by the tabulated data may be solved analy;x tically;24 however, the design conditions chosen will yield a satisfactory j approximation if used without correction for any time during the summer.; : period. Example 11: Estimate the total instantaneous rate of heat gain for a west win-. dow 3 ft wide by 5 ft high, with a setback of 6 in., for August 1 and 40 deg nortB'-.;; latitude at 3:00 pm (sun time). S Solution: From Table 13, the instaneous rate of heat Min, due to transmitted!/ : : direct and diffuse solar radiation, is 180 Btu per hr. From Table 6,0 is 45.5 deg atWjyj'. Cooling Load 321 y is 16 direct deg. solar From Equation radiation is: 5, the fraction of the total window area that is receiving cos 16 u.167 tan 16 = 1 - 0.108 - 0.048 + 0.005 = 0.851 cos 16 In this instance the convection and radiation heat gain is due principally to temperature difference, so that shading has but a small effect on that portion of the absorbed radiation. Hence, the factor 0.851 is applied o, "" instantaneous Solar Heat Gain Through Single Thickness op Common Window Glass Ttfe op Shading Canvas awning sides open Canvas awning top and sides tight against building Inside roller shade, fully drawn* Inside roller shade, fully drawn* Inside roller shade, fully drawn* Inside roller shade, half drawn* Inside roller shade, half drawn* Inside roller shade, half drawn*- . Inside Venetian blind, slats set at 45 degr Inside Venetian blind, slats set at 45 deg* Inside Venetian blind, slats set at 45 deg Inside Venetian blind, slats set at 45 deg* Outside Venetian blind, slats' set at 45 deg* Outside Venetian blind, slats fully covering window set at 45 deg*' extended t i awning Outside Venetian blind, slats set at 45 deg, extended a covering of window* awning Finish on Side Exposed to Sun Fraction op Gain Through Unbhaded Window Dark or medium Dark or medium White, cream Medium Dark White, cream Medium Dark White, cream' Diffuse reflecting aluminum metal Medium Dark White, cream White, cream White, cream 0.25 0.35 0.81 0.45* 0.75* 0.15f 0.15 0.43 Darkd* 1 g screen solar altitude 10 deg vuwjoe soauing screen solar altitude 20 deg Outside shading screen solar altitude 30 deg Outside shading screen solar altitude, above 40 deg . tint* 1 0.52 0.46 0.40 0.35 0.25 0.24 i 0.15 i 0.22 * Holler shades are assumed to be opaque. Some white shades may transmit considerable solar radia tion. For white translucent shades fully drawn use 0.55 and for hall drawn use 0.77. to preVveennettidainrebcltinrdasysarferofmullpyadssrainwgnbaentwdeceonvselrawtsi.nd.oIfws.latIstaisreafsuslulmy ecdlotsheadt(tshlaeteocsceut paatn9t0wduelga.)dujusestssalamtes fact?2 w used for roller shade fully drawn. ,, Commercial shade with wide slats. The sun may shine on window through sides of shade, Estimate ^a^Poeed portion of glass as unshaded. , ....... Commercial shade, bronze. Metal slate 0.05 inches wide 17 per inch and set at 17 deg angle with hori zontal. At solar altitudes-below 40 deg some direct solar rays are allowed to pass between slate, and this amount becomes progressively greater at low solar altit.nHoo cornea nrnrmm; , w 40 some direct solar j 1 ely *r"`r at iov solar altitude, m first paper in Reference 9. tha,,t t--hemdiiffuAstueiieradiavtiaolnuei.s niNototsehaadlseodatosmthaell: msaxmuei iteoxutexun--jt--ia-r-su-m<t-h--e-o-n-de-_i-rx-e-a-cc-tt radiation. The total instantaneous heat gain therefore is: 5 = 3 X 5 (0.851 X 180 + 26) = 2690 Btu per (hr)(sq ft) A window such as the one used in Example 11 would customarily be pro vided with an additional shading means for use particularly when directly sunlit. Conventional shading devices include awnings, shades, and screens f various types. Much experimental and analytical work conducted at the A.S.H.A.E.