Document qRZnwp3KNxpJVwxvGbDrM72j

i'ssa: 286 CHAPTER 13 1956 Guide Table 4. .Values of /d., Direct Solar Radiation Received at Normal Incidence at the Earth's Surface, and Values of /s, Diffuse or Skit Solar Radia tion, Received bt Variously Oriented Surfaces SOLAB Altitude P, Degbees Btu peb (uoun) (bquarb poot) Fob Cleab Atmospheres Fob Industrial Atmospheres Direct * Normal Radi ation Diffuse or Sxt Radiation*0 Direct4 Normal Radi ation Diffuse ob Set Radiation* AM-* l 5 10 15 20 25 30 35 40 45 50 60 70 . 80 90 pk-. 67 123 166 . 197., 218 235 248 258 .266 273 283 289 292 294 NE S W Horxz. 6 11 n 20 14 27 15 32 16 35 17 36 17 36 18 36 19 35 19 33 21 28 22 23 ---- -- ` rr- NW 44 87 11 10 13 12 15 13 17 15 19 16 21 17 23 18 25 19 27 21 29 23 -- '-- -- SE 7 14 19 23 26 28 30 31 . 32 33 34 35 -- -- Horiz. N E S W Horiz. 34 4 11 5 58 8 22 9 80 11 28 13 103 13 36 17 121 16 43 21 136 18 ' 47 24 148 19 50 27 158 20 50 30 165 21 49 31 172 22 47 34 181 ' 22 188 22 195 - __ 200 41 37 34 41 ---- -- -- 1N W18 39 7 18 9 24 12 31 16 38 18 44 21 48 23 52 25 55 27 58 30 63 34 69 ---- ---- E Hobiz. 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. 4 Derived from recommended design sol-air temperatures4 for New York City for a horizontal surfacewith bsorptivity 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 /dd, 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 287 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) L atitude Sun Time AM - i Cosine K or the Incident Angle N NE E SE S SW Hoaiz. BO z 0 6 ajd. 7 8 9 6 D.m. 5 4 3 a Q 10 11 2 1 S 12 0.267 0.144 0.030 0.862 0.752 0.604 0.427 0.234 0.039 X 5 a.m. 7 p.m. 66 07 Z8 5 4 a9 3 0.406 0.237 0.079 ______ X O Z 0 5 am. 7 pm. 6 6-.. 75 93 12 _____ 0.385 0.199 0.010 0.934 0.840 0.705 0.533 0.337 0.129 0.922 0.813 0.656 0.465 0.252 0.030 0.952 0.919 0.824 0.672 0.476 0.246 0.000 0.484 0.548 0.561 0.524 0.438 0.310 0.147 0.068 0.144 ' 0.192 .0.208 0.914" 0.951 0.919 0.824 0.673 0.475 0.246 0.000 0.358 0.505 ' 0.694 0.631 0.614 0.542 0.424 0.265 0.069 0.196 0.292 0.354 0.375 0.920 0.951 0.918 0.824 0.673 0.475 0.247 0.000 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 0.147 0.078 0.265 0.183 0.375 0.156 0.367 0.566 0.737 0.886 0.951 0.978 0.566 0.903 0.927 0.645 0.766 0.829 0.848 N NW W SW S SE Hobu. For vertical walls, if is a function of the solar altitude 0 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 fi and y are given in Table 6 for 18 deg north declination (August 1). To compute K values for orientations other than those given in Table 5, third angle <j>, the solar azimuth, is required. In this discussion, <j> 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 case <j> equals 90 + 7, that is, <j> is greater than 90 deg. The wall azimuth xf> is the angle, measured east-from south to the per pendicular to the wall for walls which have an easterly component, and west from south for those having a westerly component. For example, ft for a wall facing northeast is 135 deg. The wall solar azimuth y may be found according to the following schedule: For walls facing east of south: y = <p -- $ a.m. 7 = <$ 4- p.ta. For walls facing west of south: y == 0 + ^ a.m. y p.m. Treat negative values of 7 as if they were positive. If 7 is greater than deg, the wall is in the shade.