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280 CHAPTER 12 1951 Guide Table 12. Total Equivalent Temperature Differentials for Calculating Heat Gain Through Sunlit and Shaded Roofs Sun Tub Description op Root Construction A.M. 8 | 10 | 12 P.M. 2 |4 |8 |8 10 | 12 Light Construction Roots--Exposbd to 8 on 1# Wood1* or 1* Wood* + V or 2" Insulation 12 38 54 62 50 26 10 4 0 > Hbdium Construction Roots--Exposed to Sun 2" Concrete or 2# Concrete + X" or 2? Insulation or 2* Wood* 6 30 48 58 60 32 14 6 2* Gypsum or 2w Gypsum + V Insulation \* Wood* or ] 2" Wood* or 1 + 4" Rock Wool 29 Concrete or jin Furred Ceiling 2" Gypsum j 0 20 40 52 54 42 20 10 4m Concrete or 4' Concrete with 2* Insulation 0 20 38 50 62 40 22 12 2 6 6 Hbavt Construction Roots--Exposbd to Sun 6' Concrete 6" Concrete + 2" Insulation 4 6 24 38 46 44 32 18 12 6 6 20 34 42 44 34 20 14 Roots Cotsbbd wtth Watbb--Exposbd to Sun Light Construction Roof with 1' Water Heavy Construction Roof with 19 Water Any Roof with 6* Water 1\ tOtsSO 4 16 22 18 14 10 2 -2 -4 10 14 16 14 10 . 0 0 6: 10 10 8 4 0 6 0 Light Construction Heavy Construction Roofb with Root Sprats--Exposbd to Sun 0 4 12 is; 16 14 10 2 -2 -2 2 8 12 14 12 10 0 6 Light Construction Medium Construction Heavy Construction Roots in 8hade -4 0 6 12 14 12 8 2 0 -4 -2 2 8 12 12 10 6 2 -2 -2 0 4 8 10 10 8 4 * Includes i in. felt roofing with or without slag. May also be used for shingle roof. b Nominal thicWifn of the wood. NOTES FOR TABLE 12 Explanation: Total heat transmission from solar radiation and temperature difference between outside and room air. Btu per (hr) (sq ft) of roof area Equivalent temperature differential from above table Heat transmission coefficient for sum mer Btu per (hr) (sq ft) F deg 1. Source. Calculated by Mackey and Wright method (see reference list) and adjusted after studying ASHVE original test data. Estimated for July in 40 deg north latitude. (For sol-air temperatures used in calculations see Table 11.) For typical design day where the maximum outdoor temperature is 95 F and minimum temperature at night is approximately 75 F (daily range of temperature, 20 F) mean 24 hr tem perature 84 F for a room temperature of 80 F. All roofs have been assumed a dark color which absorbs 90 percent of solar radiation, ana reflects only 10 percent. 2. Application. These values may be used for all normal air conditioning estimates; usually without correction, in latitude 0 deg to 60 deg north or south when the load is calculated for the hottest weather. Note 6 explains how to adjust the temperature differential for other room and outdoor temperatures. 3. Ptaxed Roofs. If the roof is peaked and the heat gain is primarily uue to solar radiation, use for the area of the roof, the area projected on a horizontal plane. 4. Attic*. If the oeiling is insulated and if a fan is used in the attic for positive ventilation, the total tern' perature differential for a roof exposed to the sun may be decreased 85 percent. Cooling Load 281 j~---j-iinnt For temperature difference token outdoor maximum design temperature minus room it dif'f^reOln^'t f^roVmoisojacw'g.` sif-_Wth. e_bouetdnno*o.vrth_deejrsdiirgfafn_earteennmMcpeeirsagturereatmerin(ourswlreoeosi)m*thkteamn,, pm1e5 rdaetgur.ae.4d'i.sd4 dtthkifef.eerexcnetsfsrotom(othresubbastreaocft iL' dSiiSSw torn) "" bo" diantito. v nuidoor daUp range of temperature other than SO deg. If the daily range of temperature is less than 20 ddldffl fox every 2 deg lower daily range; if the daily range is greater than 20 deg, subtract 1 deg for kj,rW daily range. For example, the daily range in Miami, Florida is 12 deg or 8 deg lees than i + 4 d* at rfl horns o! the day. T-nkl Colon Credit should not be taken for light colored roofs except where the permanence of the light i t^Litabliahed by experience, as in rural areas or where there is little smoke. When the exterior surface ? Jxmsed to the sun is a light color, such as white or aluminum (which absorb approximately 50 percent percent of the solar radiation) add to the temperature differential for roof in shade 55 percent f,"j^MHiMbetween the roof in sun and roof in shade. When the roof exposed to the sun is a medium roloTsuih^riSbtPey* blue or green, or bright red, add 80 percent of this difference. ,^nr transmission in latitudet other (ion 40 deg north, and in other months. The table values of ternP'fgturedifferentials will be approximately correct for a roof in the following months: North Latutoi lati tude (deg) Months 0 All Months 10 30 30 40 All Months _ All Months except Nov, Dec. Jan Mar, Apr, May, June. July, Aug, Sept April, May, June, July, Aug 50 May, June, July lati tude (deg) 0 10 20 30 40 50 South Latrudb Months' All Months All Months All Months except May, June. July Sept, Oct, Nov, Dee, Jan, Feo, Mar Oct, Nov, Dec, Jan, Feb Nov, Deo, Jan For other months, the total temperature differential (tx) may be approximated by the use of the following formula: (l " W . iy `. . akere ( " temperature differential for the same wall in shade for desired time of day; obtained from Table i2. .......... r- - /m solar transmission through glass, Btu per (hr) (sq ft) for flat skylight in July, 40 deg r north latitude (Note; this is maximum value irrespective of time). Is a fraTM* as ly except use the maximum value for flat skylight, for month, and latitude desired for t*. ... --*--....... -- .It temperature differential for particular roof exposed to sun for the desired time of day from Table 12 (Hate this makei adjustment only for solor radiation and that there mag be additional correction feo out door temperature.) Tables 12 and 13 are based on an equation re-arranged from Equation 5 to read: , A7---td (6) Let tm + X <t * -- fm) = {Pl a net equivalent outdoor temperature for com bined periodic and mean heat flow. Magnitudes of fp will vary cyclically with time. Then, l-U(tr-td (7) which is a simple form analogous to the steady state equations of .Chapters 5 and 9. The rate of heat flow is obtained by multiplying the overall heat transmission coefficient of the structure by the equivalent temperature differential obtained from the tables. Tables 12 and 13 were developed by using an outside surface conductance of 4.0 and an inside film conductance of 1.65 Btu (hr) (sq ft) (F deg). A reduction was made in the temperature differentials for roofs amounting to some 20 percent of solar radiation as explained by Stewart.1* This was to compensate for several factors, one of which is the radiant heat lost to the