Document pBm3QV7JQXok6LyOvNVMae8Dk

272 CHAPTER 12 1950 Guide Table 14. Total Equivalent. Temperature Differentials fob Calculating Heat Gain Through Sunlit and Shaded Roofs Sum Tub Dcscbiftxon or Roor Construction* A.M. 8 10 | u P.M. 2 | 4 | 8 | 10 Light Combtbpctiom Roots--Exposbd to Sun 12 1' Woodb or 1' Wood* + 1' or 2* Insulation 12 38 54 62 60 26 10 4 0 Ubuxuk Construction Roots--Exposxd to Sun 2- Concrete or 2' Concrete + 1' or 2* Insulation or 2' Woodb 6 30 48 68 50 32 14 6 2 2* Gypsum or 2* Gypsum + 1' Insulation 1' Wood6 or I 2" Woodb or 1 + 4* Rock Wool 2* Concrete or fin Furred Ceiling 2* Gypsum J 0 20 40 62 54 42 20 10 6 4* Concrete or 4' Concrete with 2* Insulation 0 20 38 60 52 40 22 12 6 Hsavt Construction Roofs--Exposbd to Sum 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 COVHBED WTTH WATER--EXPOSHD TO 8UN 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 6' Water -2 0 0 6 10 10 8 4 0 6 0 Light Construction . Heavy Construction Roots with Root Sprats--Exposbd to Sun 0 4 12 18 16 14 10 2 -2 -2 2 8 12 14 12 10 0 6 Roots m Shade 1. 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 .a Includes I in. felt roofing with or without slag. May also be used for shingle roof. ** Nominal thickness of the wood. NOTES FOR TABLE 14 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* I mer Btu per (hr) ( (eq ft) F deg . Source. by Mackey and Wright method (see reference list) and adjusted after studying IMJ _I 1 a__a J.t. T?_i;--f..ln i> Aft nn*4li lafiin/ia fEVip RaI.aip tamnaratiiPM iiQaH In parature 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 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. Peaked Booft. 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. Attice. If the ia 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 osnt. Cooling Load 273 6 Correction*. For temperature difference when outdoor maximum design temperature minus room is dif ferent from 16 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 16 deg add the excess to (or subtract lbs deficiency from) the above differentials. For outdoor daily range of temperature other than tO deg. If the daily range of temperature is I** than {ft dM, 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 Florida is 12 deg or 8 deg thtn 20 deg, therefore, the correction is + 4 deg at all hours of the day. Light Colors. Credit should not be taken for light oolored 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 per cent and reflect 50 per cent of the solar radiation) add to the temperature differential for roof in shade 65 per cent of the difference between the roof in sun and roof in shade. When the roof exposed to the sun is a medium pflinr such as light grey, blue or green, or bright red, add 80 per eent of this difference. For solar transmission in latitudes other than 40 deg north; and in other months. The table values of tern- posture differentials will be approximately correct for a roof in the following : North Latttudb I*ti* tude (deg) 0 10 20 80 40 60 Months All Months All Months All Months except Nov, Deo. 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 Latttudb Months All Months All Months All Months except May, June, July Sept, Oct. Nov, Deo, Jan. Feb, Mm* Oct, Nov, Deo, Jan, Feb Nov, Dec, Jan Far other months, the total temperature differential (lx) may be approximated by the use of the following formula: h " + v (I? " W l7 vhers U * temperature differential for the same wall in shade for desired *mt of day; obtained from Table 14. lf w, iMTimnm solar transmission through glass, Btu per (hr) (sq ft) for flat skylight in' July, 40 deg north latitude (Note: this is value irrespective of time). It * mrm as If except use the maximum value tor flat skylight, for month, and latitude desired far lz> tv " temperature differential for particular roof exposed to sun fox 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 walls, be taken directly from the tables in Chapter 9 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. 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 felt roofing | 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