Document VGaJ7yk1363p8GDd08vbrXDyZ

298 CHAPTER 13 1958 Guide Table 4. Values of Id., Direct Solar Radiation Received at Normal Incidence at the Earth's Surface, and Values or Ie, Diffuse or Sky Solar Radia tion, Received by Variously Oriented Surfaces Btu per. (hour) (square foot) SODAB Altitude 0, Degrees Fob Clear Atmospheres Direct * Normal Radi ation Diffuse or Set Radiation * For Industrial Atmospheres Direct*1 Normal Radi ation Diffuse oh Skt Radiation* c AM -> i NE s W Horiz. NE s w Horiz. 5 67 6 11 4 4 7 34 4 11 5 3 9 10 123 11 20 8 7 14 58 8 22 9 7 18 15 166 ' 14 27 11 10 19 80 11 28 13 9 24 20 197 15 32 13 12 23 103 13 36- 17 12 31 25 218 16 35 15 13 26 121 16 43 21 16 38 30 235 17 36 17 .15 28 136 18 47. 24 18 44 . , 35 248 17 36 19 16 30 148 19 50 27 21 48 40 258. 18 36 21 17 31 158 20 50 30 23 52 45 .266 ' 19 35 23 18 32 165 21 49 31 25 55 50 273 19 33 25 19 33 172 22 47-- 34 27 58 60 283 21 28 27 21 34 181 22 41 ` 37 30 63 70 289 22 23 29 23 35 188 22 34 . 41 34 69 80 292 -------- -- 195 -- -- -- -- -- 90 294 -- ---- -- 200 -- -- -- -- -- N W S E Horiz. N W S E Hobu 4 Moon's4 proposed standard for sea level, 20 mm precipitable water vapor, 300 dust particles per cu cm, 2.8 mm Hg partial pressure of ozone. b For 40 deg north latitude on about August 1. c Based on observations by ASHAE Laboratory at Cleveland on cloudless days during which the observed normal incidence values closely approximated the normal incidence values tabulated. ^ Derived from recommended design sol-air temperatures4 for New York City for a horizontal surface with absorptivity of 1.0. values of the order of those given for industrial atmospheres are usually associated with dry-bulb and wet-bulb temperatures near the design values of 95 F and 75 F (67 F dew-point). On the other hand, values approaching or exceeding those for a clear atmosphere are often encountered during Cleveland summers, but with dew-point and maximum dry-bulb temperatures 10 to 15 deg lower. Considerable judgment, therefore, is required in selecting solar intensity values for design purposes. Data regarding the irradiation of vertical and horizontal surfaces by diffuse or sky radiation are few. Suggested design values for a 40-deg latitude on August 1 (18 deg declination, north) are given in Table 4 for the two types of atmospheres. These are based upon observations made on cloudless days in Cleveland over a period of several summers. Since less extensive data were available for industrial atmospheres, there is more uncertainty regarding these values. In both instances, the values include an unknown amount of ground reflection, which may be expected to vary with location. It should be noted that clouds which do not obscure the sun tend to increase diffuse radiation values. Nearby buildings may reduce diffuse irradiation by partial shading. Calculation Tables The irradiation of a surface by the sun is the product of Id,,, the direct normal radiation (see Table 4), and the cosine K of the incident angle, 9. For horizontal surfaces, the cosine K equals the sine of the solar altitude. Cooling Load 299 Table 5. Values of K, the Cosine of the Incident Angle, for Variously Oriented Walls and a Horizontal Surface Computed for 18 Deg Declination, North (August 1) a a Sun Time Cosine K or the Incident Angle S AM - N NE E SE S SW Horiz. 6 aAn. 6 p.m. 75 o8 4 Z9 3 10 1! 12 2 1 5 ajn. 7 p.m. (5 6 7 6 5 Z6 4 ou 9 Q 10 o 11 3 2 1 12 5 ajn. 7 p.m. 66 o7 5 Z8 4 39 10 s 11 3 2 1 plf - 0.267 0.1440.030 0.862 0.752 0.604 0.427 0.234 0.039 0.406 0.237. 0.079 0.934 0.840 0.705v 0.533' 0.337 0.129 0.385 0.199 0.010 0.922 0.813 0.656 0.465 0.252 0.030 N NW 0.652 0.919 0.824 0.672 0.476 0.246 0.000 0.914 0.951 0.619 0.824 0.673 0.475 0.246 0.000 0.920 0.951 0.918 0.824 0.673 0.475 0.247 0.000 W 0.484 0.548 0.561 0.524 0.438 0.310 0.147 0.068 0.144 0.192 0.208 0.358 0.505 0.594 0.631 . 0.614 0.542 0.424 0.265 0.069 0.196 0.292 0.354 0.375 0.378 0.532 0.643 0.700 0.699 0.642 0.532 0.375 0.166 0.316 0.433 0.505 0.530 sw S 0.147 0.076 0.265 0.163 0.375 SE 0.156 0.367 0.566 0.737 0.866 0.951 0.978 0.009 0.199 0.391 0.566 0.713 0.829 0.903 0.927 0.078 0.233 0.399 0.545 - 0.669 0.766 0.829 0.848 Horiz. For vertical walls, A is a function of the solar altitude /S and the wall solar azimuth y, thus These three angles are defined in Fig. 1. Values of K are given in Table 5 and values of /3 and y are given in Table 6 for 18 deg north declination (August I). compute K values for orientations other than those given in Table 5, third angle <t>, the solar azimuth, is required. In this discussion, 0 will be measured east from south in the morning, and west from south in the after noon. Hence, <j> values are equal to 90 deg minus the y values for an east or west facing wall, except when Table 6 shows the south walls to be in the shade. In this ease <f> equals 90 + 7, that is, 4> is greater than 90 deg. ^*.e wall azimuth \f/ is the angle, measured east from south to the per pendicular to the wall for walls which have an easterly component, and west rom south for those having a westerly component. For example, d- for a wall facing northeast is 135 deg. schedule^ so^ar azTMuth y may be found according to the following wans lacing east of south: 7 = 0 -- ^ a.m. 7 -- <t> + $ p.m. ror wans iacmg west oi soutn: 7 " 4> + ^ a.m. y a# 0 -- $ p.m. qrT!?i.n^?ative va^ues of 7 as if they were positive. If y is greater than eS> wall is in the shade.