Document 7OoJZd4OZ5NeE86xrdEnR6ZY8

284 -CHAPTER 13 Table 9. Total Equivalent Temperature Differentials fob CalcclatinqU; Heat Gain Through Sunlit and Shaded Roofs Sun Time Description op Roof-Construction* Light Construction Roofs--Exposed to Sun Woodb or 1" Wood0 -4- 1' or 2' Insulation 12 38 54 62 50 26 10 ,4 0 Medium Construction Roofs--Exposed to Son 2* Concrete or 2' Concrete + 1' or 2" Insulation or 2' Wood0 'O' 6 30 48 58 50 32 14 6 2`. 2" Gypsum or T Gypsum + 1" Insulation 1" Woodb or 1 2" Woodb or 1+ i" Rock Wool 2* Concrete or [in Furred Ceiling 2' Gypsum j f 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 4- 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 0 4 16 22 18 14 10 2 0 Heavy Construction Roof with 1* Water -2 -2 -4 10 14 16 14 10 6 Any Roof with 6' Water -2 0 0 6 10 10 8 4 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] Explanation: radiation and temperature difference I between outside and room air. Btu [ per (hr) (sq ft) of roof area j I (Equivalent temperature differential from above table (Heat transmission v JcoefficientforsiHO' A jmer Btu per (nx) 1(eq ft) (F deg) 1. Source. Calculated by Mackey and Wright method (see reference list) and adjusted after studyj?l HVE oriemal test data. Estimated for July in 40 dee north latitude. (For sol-air temperatures used minimum temperature at nignt is approximately to r latuijr range UJ temperature, iur; uieau *1 im --g. 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. Rote 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 fox ^ area of the roof, the area projected on a horizontal plane. . 4. Attic*. If the ceiling is insulated and if a fan is used in the attic for positive ventilation, the total perature differential for a roof exposed to the sun may be decreased 25 percent. .Cooling load 285 5. Corrections. For temperature difference token outdoor maximum design temperature .minus room ie dif ferent from tS 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 tbs 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 dek, add 1 deg for every 2 deg lower daily range; if the daily range is greater than 20 deg, substract 1 deg for every 3 deg higher daily range. For example, the daily range in Miami, Florida is 12 aeg or 8 deg less than 20 deg, therefore, the correction is -f 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 culuf is established by experience, as m rural areas or where there is little smoke. Wnen 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 radiatiqn)-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 10 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 All Months 20 AU Months except Nov, Dec, Jan 30 Mar, Apr, May, June. Julv. Aue. Sect 40 April. May. June. Julv. Aus 50 May, June; July South Latitude Lati- tude (deg) Months 0 All Months 10 All Months 20 All Months except Mav. June, Julv 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 (fx) may be approximated by the use of the following <*-< + 7s <* - V ty where t = temperature differential for the same roof in shade for desired time of day; obtained from Table fy -- maximum solar transmission through glass, Btu per (hr) (sq ft) for flat skylight in July, 40 deg north latitude {Note: this is maximum value irrespective of time). f* * same as Iy except use the maximum value for flat skylight, for month, and latitude desired for *. tv -- temperature differential for particular roof exposed to sun for the desired time of day from Table .__[*fote that this makes adjustment only for solar radiation and that there may be additional correction for outsoot temperature.) air temperature t,, is the temperature of the outdoor air, which, in the . ser,ce of all radiation exchanges, would give the same rate of heat entry into the surface as would exist with the actual combination of incident solar radiation, radiant energy exchange with the sky and other outdoor sur roundings, and convective heat exchange with the outdoor air. The sol-air temperature data5,610 as developed by Mackey and Wright or an industrial atmosphere were used as a basis for preparing Table 8 snowing summer design sol-air temperatures. Sol-air temperatures may also be estimated from experimental observation of surface temperatures i walls and roofs which appear in the literature.11'12 Both analytical and experimental studies have been made on the problem10 of heat flow through Jails and roofs. Those concerned with a further study of the details of oolmg-load estimates in particular relation to periodic heat flow will find U?i va^ue and interest in the reports of experimental studies of these Problems.10'11 12131415 The reader may also refer to the Cooling Load ,, jPter of The Guide 1952 for the theory of heat flow through walls and roofs