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304 CHAPTER 13 1958 Guide; ; Table 9. Total Equivalent Temperature Differentials fob Calculating Heat Gain Through Sunlit and Shaded Roofs Sun Time Description op Roop Construction* A.M. 8 I 10 1 12 2 I4 P.M. | 8 | |10 12 Light Construction Roofs--Exposed to Sun 1" Woodb or 1* Woodb + 1* or 2" iDsulation 12 38 54 62 50 26 10 40 Medium Construction Roofs--Exposed to Sun 2" Concrete or 2* Concrete + 1* or 2" Insulation or 2' Woodb 6 30 48 58 50 32 14 6 2 2' Gypsum or 2' Gypsum + 1# Insulation 1' Woodb or 2" Woodb or 4- 4" Rock Wool 2* Concrete or in Furred Ceiling 2" Gypsum 0 20 40 52 54" 42 20 10 6 4' Concrete or 4' Concrete with 2' Insulation 0 20 38 50 52 40 22 12 6 Heavy Construction Roofs--Exposed 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 Roofs Covered with Water--Exposed to Sun Light Construction Roof with 1' Water Heavy Construction Roof with 1* Water Any Roof with 6' Water 0 4 16 22 18 14 10 2 -2 -2 -4 10 14 16 14 10 -2 0 0 6 10 10 8 4 0 6 0 Light Construction Heavy Construction Roofs with Roof Sprays--Exposed to Sun 0 4 12 18 16 14 10 2 -2 -2 2 8 12 14 12 10 0 6 Light Construction Medium Construction Heavy Construction Roofs in Shade -4 0 -4 -2 -2 --2 6 12 14 12 8 2 8 12 12 10 0 4 8 10 10 20 62 84 * Includes I in. felt roofing with or without slag. May also be used for shingle roof. bNominal thickness of the wood. NOTES FOR TABLE 9 (Total heat transmission from solar radiation and temperaturedifference between outdoor and room air. Btu per (hr) (sq ft) of roof area Heat transmission v Icoefficientforsum* * lmer Btu per (nr) l(sq ft) (F deg) 1. Source. Calculated by Mackey and Wright method (see reference list) and adjusted after studying ASHAE original test data. Estimated for about August 1 in 40 deg north latitude. (For sol-air temperature* used in calculations see Table 8.) For typical design day where the maximum outdoor temperature is S&r. and minimum temperature at night is approximately 75 F (daily range of temperature, 20 F) mean 24 hr tear perature 84 F for a room temperature of 80 F. All roofs have been assumed a dark color which absorbs percent of solar radiation, and reflects only 10 percent. 2. Application. These values may be used for all normal air conditioning estimates; usually withou correction, in latitude 0 deg to 50 deg north or south when the load is calculated for the hottest weather. N 5 explains how to adjust the temperature differential for other room and outdoor temperatures. 3. Peaked Roofs. If the roof is peaked and the heat gain is primarily due to solar radiation, use for ^e. area of the roof, the area projected on a horizontal plane. ' 4. Attics. If the ceiling is insulated and if a fan is used in the attic for positive ventilation, the total teffl . perature differential for a roof exposed to the sun may be decreased 25 percent. 1 Cooling Load 305 5. Corrections. For temperature difference uhen outdoor maximum design iemperaiure minus room is dif ferent from IS deg. If the outdoor design temperature minus room temperature is different from the base of 15 deg, correct as follows: When the difference is greater (or less) than 15 deg add the excess to (or subtract the deficiency from) the above differentials. For outdoor daily range of temperature other than SO deg. If the daily range of temperature is less than 20 deg, add 1 deg for every 2 deg lower daily range; if the daily range is greater than 20 deg, subtract 1 deg for every 2 deg higher daily range. For example, the daily range in Miami, Florida is 12 deg or 8 deg less than 20 deg, therefore, the correction is + 4 deg at all hours of the day. Light Colors. Credit should not be taken for light colored roofs except where the permanence of the light color is established by experience, as in rural areas or where there is little smoke. When the exterior surface of roof exposed to the sun is a light color, such as white or aluminum (which absorb approximately 50 percent and reflect 50 percent of the solar radiation) add to the temperature differential for roof in shade 55 percent of the difference between the roof in sun and roof in shade. When the roof exposed to the sun is a medium color such as light grey, blue or green, or bright red, add 80 percent of this difference. For solar transmission in latitudes other than !fl deg north, and in other months. The table values of tem perature differentials will be approximately correct for a roof in the following months: North Latitude Latitude (deg) Months > 0 All Months 10 AU Months 20 All Months except Nov, Dec, Jan 30 Mar, Apr, May, June, July. Aug. Sept 40 April. May. June. July. Aue 50 May, June, July South Latitude Lati- tude (deg) Months 0 All Months 10 All Months 20 All Months except May, June, July 30 Sept, Oct, Nov, Dec. Jan. Feb. Mar 40 Oct, Nov, Dec, Jan, Feb 50 Nov, Dec, Jan For other months, the total temperature differential (tx) may be approximated by the use of the following formula: tx ~ t* + (< -- ta) ty where = temperature differential for the same roof in shade for desired time of day; obtained from Table iy -- maximum solar transmission through glass, Btu per (hr) (sq ft) for flat skylight in Aug., 40 deg north latitude (Note: this is maximum value irrespective of time). /* = same as 7y except use the maximum value for flat skylight, for month, and latitude desired for tx. *V = ^emPera*ure differential for particular roof exposed to sun for the desired time of day from Table (Note that this makes adjustment only for solar radiation and that there may be additional correction for out door temperature.) Examples of Use of Equivalent Temperature Tables Example 5: Given: A roof is constructed of 6 in. of stone concrete with 2 in. of insulating board and tar felt roofing | in. thick, and is exposed to the sun. The loca- at9 nri e ce2tral Part the United States. Find the rate of heat flow into building perature 80 July for an outdoor design temperature 95 F, and an inside tem- Trom.TabIe 2 p.m. column for 6 in. concrete plus 2 in. insulation, mice* 6 * .e9uivalent temperature differential 34 deg. The overall heat transhoo/fl11 coeclent for summer is taken from Table 11 and is found to be 0.13. The neat How rate equals 34 X 0.13 = 4.42 Btu per (hr) (sq ft). F?r the conditions of Example 5, find the rate of heat flow into build- door) * n J^y tor design temperatures of 105 F (outdoor) and 78 F (in- 7c pv, . range of temperature 30 deg, t.e., outdoor temperature minimum of S l CCUrs or 5-00 a.m.; this being 30 deg less than the maximum. .^%ke correction in equivalent temperature differential in accordance ^th Note 5 in Table 9 as follows: e correction for 27 deg design temperature difference is (27 -- 15) = + 12. The correction for 30 deg daily range is ^ --= -- 5. Th* Ltal correction is + 12 - 5 = + 7. e heat flow rate at 2:00 p.m. is (34 + 7) X 0.13 = 5.32 Btu per (hr) (sq ft).