Document NyYoEOegmxrjNLqJagdG909D

CHAPTER 13 1956 Guide Table 9 Total Equivalent Temperature Differentials for Calculating Heat Gain Through Sunlit and oiiaueu Ropfs Description op Roof Construction 1" Woodb or 1" Woodb + 1" or 2" Insulation P.M. 28 | 10 12 4 6 8 10 12 oofs--Exposed to Sun 12J 38 54 62 50 26 10 4 0 Cooling Load 293 5. Corrections. For temperature difference when outdoor maximum design temperature minus room is^dif-' ferent from 15 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 0 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, substract 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 40 deg north, and in other months. The table values of tem perature differentials will be approximately correct for a roof in the following months: Medium Construction Roofs--Exposed to Sun North Latitude South Latitude .'2" 2" Concrete Concrete or + 1" or 2" Insulation or .2* Woodb 6 30 48 58 50 32 14 , 2 Lati tude (deg) * Months Lati tude (deg) . ' Months 2" Gypsum or 2' Gypsum + 1" Insulation 1* Woodb or 1 2" Woodb or i+ V 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 I0 20 38 50 52 40 22 12 1 l Heave Construction Roofs--Exposed to Sun 0 All Months 10 All 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 iS All Months Ail 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 orraula: fx = fa + iy (tv -- fa) 6' Concrete 6" Concrete + 2' Insulation 46 42 Roofs Covered with Water--Exposed to Sun Light Construction Roof with 1* Water Heavy Construction Roof with 1" Water Any Roof with 6' Water 4' 16! -2 -4 00 44 32 44 34 14 10 16 14 10 8 12 14 2 10 4 where fa = temperature differential for the same roof in shade for desired time of day; obtained from Table 9. ly ~ maximum solar transmission through glass, Btu per (hr) (sq ft) for fiat skylight in Aug., 40 deg * north latitude (Note: this is maximum value irrespective of time). It =* same as 7y except use the maximum value for fiat skylight, for month, and latitude desired for fx. ' fv = temperature differential for particular roof exposed to sun for the desired time of day from Table (Note tkat this makes adjustment only for solar radiation and that there may be additional correction for out door temperature.) Roofs with Roof Sprays--Exposed to Sun Light Construction Heavy Construction 0 4| 12 18 -2 -2 2 8 16 12 14 14 10 12 2 10 Roofs in Shade Light Construction Medium Construction Heavy Construction 0 --2l -2' a Includes fin. felt roofing with or without slag. May also be used for shingle roof. ^Nominal thickness 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 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 at 2:00 p.m. during July for an outdoor design temperature 95 F, and an inside tem perature 80 F. Solution: From Table 9 in 2 p.m. column for 6 in. concrete plus 2 in. insulation, find the total equivalent temperature differential 34 deg. The overall heat trans mission coefficient for summer is taken from Table 11 and is found to be 0.13. The heat flow rate equals 34 X 0.13 = 4.42 Btu per (hr) (sq ft). of the wood. NOTES FOR TABLE 9 Total heat transmission from solar] [radiation and temperature differencel between outside and room air. Btu | per (hr) (sq ft) of roof area Equivalent temperaturel ^ idifferential from above! table Heat transmission] coefficient for sum-1 mer Btu per (r)| (sq ft) (F deg) Example 6: For the conditions of Example 5, find the rate of heat flow into build ing at 2:00 p.m. during July for design temperatures of 105 F (outdoor) and 78 F (in door). Daily range of temperature 30 deg, t.e., outdoor temperature minimum of '5 F which occurs at 4:00 or 5:00 a.m.; this being 30 deg less than the maximum. Solution: Make correction in equivalent temperature differential in accordance with Note 5 in Table 9 as follows: ' 'li AuasnSedHdmAiniEnciomarlciuguminlaattielomtnespstesuernaewtuTr.aebaUletU8nU.i)gMhHFis.oUarp.tvyp.pr_oi_cx_ai_ml__da_et_es__ilgy_n75dFay(wdahielyrerathnegemoaf xteimmupmeraotuutrdeo,o2r0tFem) mpeeraantu2r4ehr-t-e-m The correction for 27 deg design temperature difference is (27 -- 15) *= + 12. perature 84 F for a room temperature of 80 F. All roofs have been assumed a dark coior which absorbs w perc2.enAtpopf lsicoalatirorna. diTahtieosne, avnaldueresflmecatsy obnelyus1e0d pfeorrceanllt.normal air conditioning estimates; usually without' (30_20\ ----- ^-- ) = -- 5. correction, in latitude 0 deg to 50 deg north or south when the load is`calculated for the hottest weather. Note 5ex3p.laPinesakbeodwRtoooafsd. juIsft tthhee treomofpiserpaetuarkeeddiaffnedretnhteiahl feoartogtahienr irsoopmrimanadriloyudtduoeotrotesmolpaer rraatduiraetsio. n, use for the area of the roof, the ares 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 Net total correction is + 12 -- 5 = +7. The heat flow rate at 2:00 p.m. is (34 + 7) X 0.13 = 5.32 Btu per (hr) (sq ft). perature differential for a roof exposed to the sun may be decreased 25 percent.