Document ppZMnLnrbnzKj5gkjMRn1ejkw

.286 CHAPTER 15 1949 Guide Table'10. Summer Design Sol-Air Temperatures for New Yobs, N. Y. (North Latitude 4046'; Elevation 180 Ft) Mean Sun Time b Ratio: ---- fo 12 midnight 1 a.m. 2 3 4 5 6 7 8 10 11 12 noon 1 p.m. 2 3 4 5 6 7 8 9 10 11 24-hr avg, fa Sol-Air Temperature, to Fahrenheit Decrees Any Surface^ Horizontal North East South 0 0.25 0.25 0.25 0.25 79 78 . 7777 76 76 76 80 82 86 88 90 92 93 94 94 94 93 90 88 85 83 82 81 84.8 79 78 77 77 76 76 81 96 ' 110 . 127 137 148 155 154 152 144 136 121 106 93 85 83 82 81 106.4 79 78 77. 77 - 76 76 80 85 . 85 ` 90 92 94 97. 98 99 99 99 103 106 102 85 83 82 81 88.5 79 78 77 77 76 76 89 106 114 120 114 106 97 98 99 99 99 97 93 90 85 83 82 81 92.3 79 78 77 77 76 76 77 82 86 97 104 111 115 117 112 102 99 97 93 ' 90 85 83 82 . 81 90.7 West 0.25 79 78 77 77 ' 76 76 77 82 85 90 92 94 98 108 126 136 145 - 140 134 115 85 83 82 81 96.5 6 -- surface absorptivity, dimensionless. /o " unit convective conductance, Btu per (hr) (sq ft) (F deg) b Values in this column are magnitudes of to, the outdoor air temperature. Table 11. Summer Design Sol-Air Temperatures for Lincoln, Nebr. (North Latitude 4050'; Elevation 1225 Ft) Mean . .Sun Time b Ratio: --1-- /o 12 midnight 1 a.m. 2 3 4 5 6 7 8 9 10 11 12 noon I p.m. *2 3 4 5 6 7 8 -9 10 11 24-hr avg. fa Sol-Air Temperature, fa Fahrenheit Degrees Any Surface^ Horizontal North East South 0 0.25 0.25 0.25 0.25 89 88 86 84 84 82 81 82 88 93 96 100 102 404 ' 106 107 107 ; 106 105 102 98 94 92 .. 90 89 88 86 84 84 82 87 103 124 143 160 172 178 180 178 170 ' 158 142 126 109 99 94 92 90 94.4 121.6 89 88 . 86 8484 82 88 93 94 98 102 106 108 110 112 . 113 112 113 117 113 08 94 92 90 98.6 89 88 86 : 84 - 84 . \ 82 100 125 137 142 . 138 129 . 115 110 112 113 112 110 108 104 98 94 . 92 90 105.9 89 88 86 84 84 82 82 85 92 104 . 115 125 130 132 131 126 117 110 108 104 98 94 92 90 . . 102.1 . West :. 0.25 .89 88 86 84 . 84 82 82` 85 92 98 102 106 108 119 137 150 158' 157 149 128 98 94 ; 92 90 . 106.6 * 6 = surface absorptivity, dimensionless. ft, a unit convective conductance, Btu per (hr) (sq ft) (F deg). bValues in thla column are magnitudes of to, the outdoor air temperature. Cooling Load 287 2..To adjust tihe data in Tables 10 and 11 for variations in t>: a. Establish the magnitude of i',, at the locality in question. b. Determine the difference (t'0 -- <,). c. Add (algebraically) the difference'(i. -- fa).to the data tabulated. 3. To adjust the data in Tables 10 and 11 to other magnitudes of 6//. than 0.25: a For New York or Lincoln, merely interpolate or extrapolate the tabulated data by direct proportion, using the column for b/f,, = 0. b. For other localities, first determine t\ = t'o + b/f0 I't for 5//. = 0 and 6//. = 0 25. Then interpolate or extrapolate by direct proportion as before. Sol-air data for a particular locality may be adjusted for different azimuths of the vertical surface in question in a similar maimer; although, all things considered, a simple interpolation between the four points of the compass should serve for all but the most accurate calculations. An example of the use of the tables in determining sol-air temperature is given. Example S. Find the summer design sol-air temperature in New York, N. Y., for a west wall which has a solar absorptivity of 0.7, at a sun time of 3:00 p. m. b 0.7 Use/. = 4; then -- for this wall is -- or 0.175. From Table 10: for -- Jo polation for this wall: 0, t. = 94 F; for -- / 0.25, t. 136 F; and by linear inter- t. = 94 + (136 - 94) = 94 + 29 = 123 F. 0.25 Sol-air temperatures are especially helpful in the calculation of periodic heat transfer, as will be illustrated in the material which follows. PRINCIPLES OF PERIODIC HEAT FLOW Calculation principles for periodic heat flow are dealt with briefly injthis section; in the section which follows, practical tables are given to facilitate rapid design estimates. In addition to the rate of heat entry into the outside building surface these tables take into account the following factors: 1. The thermal conductivity of material. 2. The density, specific heat and character of material. 3. Thickness of material. 4. Room air temperature. 5. - Unit convective conductance between the inside surface and room air; and radiant heat transfer between the inside surfaces and other surfaces in the room: Time Lag The fundamental analysis of periodic heat flow is complicated when compared with steady-state calculations on account of the time-variable storage of heat from point to point through a wall or roof. The cyclic variation of outdoor conditions produces a related cyclic variation of tem perature and heat flow throughout each structural section exposed to the weather. The cyclic variations undergo a progressive shift in phase and