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294 CHAPTER 15 1949 Guide Table 14. Total Equivalent Temperature Differentials for Calculating Heat Gain Through Sunlit and Shaded Roofs Sun Time Description op Root Construction* A.M. 8 | |10 12 P.M. 2 | 4 | 0 | 8 | 10 | 12 Light Construction Roots--Exposed to Sun 1* Wood6 or 1" Wood6 + 1* or 2* Insulation I 12 38 54| 62 50 26 10 4 0 Medium Construction Roofs--Exposed to Sun 2* Concrete or 2" Concrete + 1* or 2? Insulation or 2* Wood6 6 30 48 58 50 32 14 6 2 2a Gypsum or 29 Gypsum + 1" Insulation I* Wood6 or 1 2* Wood6 or 14* 4" Rock Wool 2" Concrete or [in Furred Ceiling 2" Gypsum J 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 Hbavy 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 0 4 16 22 18 14 10 2 Heavy Construction Roof with 1" Water -2 -2 -4 10 14 16 14 10 Any Roof with Water -2 0 0 6 10 10 8 4 0 6 0 Light Construction Heavy Construction Roofs with Roof Sprats--Exposed to Sun 0 4 12 18 16 14 10 2 -2 -2 2 8 12 14 12 10 0 6 Roofs in Shade Light Construction Medium Construction Heavy Construction -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 J in. felt roofing with or without slag. May also be used for shingle roof. 6 Nominal thickness of the wood. NOTES FOR TABLE 14 Total heat transmission from solar Heat transmission IExplanation: radiation and temperature difference between outside and room air. Btu per (hr) (sq ft) of roof area Equivalent ternperature differential from above X coefficient for sum mer Btu per (hr) table (eq 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 13.) 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 per cent of solar radiation, and reflects only 10 per cent. 2. Application. These values may be used for all normal air conditioning estimates; usually without correction, in latitude 0 de" to 60 deg north or south when the load is calculated for the hottest weather. Note 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 the 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 tem perature differential for a roof exposed to the sun may be decreased 25 per cent. Cooling Load 295 5. Corrections. For temperature difference when outdoor maximum design temperature minus room u dif ferent from IB deg. If the outdoor design temperature minus room temperature ts 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 to deg. If the daily range of temperature is less than 20 j__ jJjd i 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 deuly 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 exoept 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 per cent and reflect 50 per cent of the solar radiation) add to the temperature differential for roof in shade 55 per cent 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 per cent of this difference. For solar transmission in latitudes other than tfi 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 tude (deg) 20 30 40 50 Months All Months AU Months A1J Months except Nov, Dec, Jan Mar. Apr. May, June, July, Aug, Sept April, May, June, July,-Aug May, June, July Latitude (deg) 0 10 20 30 40 50 South Latitude x Months AU Months All Months All Months except May, June. July Sept. Oct, Nov, Dec, Jan, Feo, Mar Oct, Nov, Dec, Jan, Feb Nov, Dec, Jan For other mouths, the total temperature differential (fz) may be approximated by the use of the following formula: * = * + -r^ (It h f*) where U = temperature differential for the same wall in shade for desired time of day; obtained from Table 14. Jy ss 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). 1, = same'as Jy except use the maximum value for flat skylight, for month, and latitude desired for tx. tr -- temperature differential for particular roof exposed to sun for the desired time of day from Table 14. (Note that this makes adjustment only for solar radiation and that there may be additional correction for out door temperature.) on 6.0 and 1.65, it is recommended that the overall coefficient U, for walk, be taken directly from the tables in Chapter 6 in which they are based on an outside film conductance of 6.0, corresponding to a 15 mph wind velocity. Advantages of Equivalent Temperature Differential Method 1. The total,sensible heat flow is obtained by multiplying the, overall `heat transmission coefficient, U, and the equivalent temperature differen tial indicated in Tables 14 and 15. 2. The temperature differentials listed for a few representative types of construction may be used on all classes of walls and roofs, even though' the overall heat transmission coefficient is different, provided the structure has thermal and physical properties similar to one of those listed in Tables 14 and 15. 1 * * * 5 3. Adjustments can be made, according to instructions given in the foot notes for room and outdoor conditions different from those on which the tables are based. Examples of Use of Equivalent'Temperature Tables Example 6. Given: A roof is constructed of 6 in. of stone concrete with 2 in. of insulating board and tar feltroo&ng f in. thick; and is exposed to the sun. The loca tion is the central part of the United States. Find the rate of heat flow into building