Document ZBLwE7334ERdY09D9nKnEL8dY

506 CHAPTER 27 1965 Guide And Data Book sent the [FdId + Fdi\ term in Equation 2 for this one type of glass. Values in bold-face type (Tables 11 through 17) are for hours when the sun is striking the fenestration, light-face type for fenestration in the shade. In the prediction of the heat transfer due to difference in indoor and outdoor air temperatures a reasonable outdoor design temperature must be chosen. Table 1 lists outdoor dry-bulb' temperatures for summer conditions. These values may be used for June through September with good accuracy. For other months, lower temperatures apply. Data in this regard are limited, and the choice of temperature must be determined based on local weather experience. Winter design data for heating should not be-used for estimating winter cooling requirements. Somewhat higher temperatures close to the maximum expected for each month are recommended. U values for all common fenestration are shown in Table 18 for a wind speed of 7$ mph. Tables 19 through 22 present Shading Coefficient! for com monly used combinations of flat glass and shading devices. The Shading Coefficient is the ratio of the heat gain due to transmitted and absorbed solar energy by the fenestration being considered to the heat gain due to transmitted and ab sorbed solar energy by unshaded double-strength sheet glass For most types of fenestration, the Shading Coefficient remains constant within the normal accuracy of air-condi tioning load predictions. In the instances where this is not the case, the variations are explained in the text. The equation for total heat transfer (Equation 2) may be written in the alternate form: [q/A] = S[FmIo 4- + [t/(C --/<)] (3) where q/A " instantaneous rate of heat transfer, Btu per (hour) (square foot). 8 " Shading Coefficient for fenestration being con sidered. Feh, TM ratio of the solar heat pun for double strength sheet glass to the incident direct and diffuse solar radi ation, respectively, dimensionless. Id, Id " incident direct'and diffuse solar'energy, respec tively, Btuper (hour) (square foot). V overall coefficient of heat transmission, Btu per (hour) (square foot) per (Fahrenheit degree). C, f,- " outdoor and indoor air temperature, respectively, Fahrenheit. This equation in block form becomes: ["Total heat transfer-} {"Shading "1 v fSolar Heat "1 Lthrough the glass J [_CoeffiaentJ * LGain FactorJ Heat transfer due to [differences in outdoor and I indoor air temperatures J Brief discussions of each table of Shading Coefficients fol low. Table 19. Single Glass and Insulating Glass--No Shading. Shown in this table are Shading Coefficients for the types of glass in common use as fenestration. Fju.h is identified by type, nominal thickness, and approximate transmittance of normal incident direct solar energy. Generally each gt<ra manufacturer publishes or is able to furnish upon request these three items regarding each glass he produces. Hie Shading Coefficients listed in the column headed Glass in Sim should be used with the Solar Heat Cain Factors shown in bold face type in Tables 11 through 17 The coefficients shown in the column headed Glass in Shade should be used with the light face values. Values in Table 19 may be interpolated or extrapolated. If the normal incident solar transmittance of a type of glag not listed is known, a simple plot of solar transmittance versus 1 Shading Coefficient will yield the Shading Coefficient for the unlisted glass type. This applies to all types of single glass and' insulating glass when-the inner pane is regular sheet or plate ' glass. Insulating units are normally manufactured in this manner. Tables SOA and SOB. Single Glass with Indoor Shading. When some sun control is incorporated with glass fenestration, small differences in the solar transmittance mid absorptance properties of the glass become negligible from a practical airconditioning load viewpoint. It is reasonable to group various glass types as is done in these tables. Table 20A gives Shading Coefficients for Venetian blinds and roller shades. Table 20B gives Shading Coefficients for draperies. Specific physical and thermal properties of the shading devices included in Tables 20A and 20B are shown in Table 23. If the properties of the actual shading device to be used are not specifically known, the value in Table 20A or 20B which most closely approximates these properties should be used. Care should be used in interpolating and ex trapolating values in Tables 20A through 22.M""4# Draperies of fabric materials may be defined as to the color or shade of the yam, Le., light, medium, or dark, and alao the weave of the fabric in regard to the open area occurring between the yams or fibers. The light, medium, and dark colors of the yams is in terms of light reflectance. Yam reflectance differs from fabric reflectance because of the openness of the weave. To obtain yam reflectance, divide the overall fabric reflectance by the term one minus the openness factor. Hie weave of the fabric may be classified as open, semi-open, and closed, ex pressed as a percentage of open area to overall area of the fabric.- 7 A. method of classifying drapery fabrics is shown in Kg. 3. The openness of a drapery fabric affects' the amount of radi ation and reradiation energy falling ..upon individuals near window areas, and thereby affecting thermal comfort. Open ness also is one factor determining glare reduction, outward vision, and privacy. It should be noted that when a drapery is open, its condensed folds which may remain over the glas opening can constitute relatively effective insulatiou. The shading coefficients for draperies occurring in Tables 20B and 21B correspond with the classification method of Fig. 3, and are for draperies of 100 percent fullness (twice as much width of fabric as width of space covered by the drapery). Tables SIA and SlB. Insulating Glass with Indoor Shading. Refer to earlier text under heading Tables SOA and SOB, Single Glass with Indoor Shading for description of shading devices. As noted below Tables 21A and 21B, the Shading Coefficients apply for any air space thickness. {Continued on p. 610) A^jr.ConditioViing Cooling Load 507 Table 11 .... Solar.Heat Gain Factors*--Btuh per Square Foot--for June 21: Latitude i 1 D IL ! North < North Sun Toneb AMi-* 7 :9 10 . 12 N 7 -8 19 ~10 11 12 N .7 8 -9 10 11 ' 12 N N 35 43 36 26 22 22 24 39 34 22 18 20 22 23 40 25 16 18 20 21 22 NE 100 164 166 137 91 44 . 24 120 162 153 115 65 27 23 136 157 138 93 43 22 22 E 102 178 194. - 172 123 61 24 126 186 196 172 123 61 23 145 > 192 * 197 172 122 59 22 SE S 38 83 . . 100 96 73 43 24 5 10 15 18 20 22 25' 49 6 94 11 118 16 118 19 100 26 67 36 32 41 62 106 134 139 125 94 . 51 * 7 12 17 30 48 67 73 sw 5 10 15 18 20 22 24 6 11 15 18 20 - 22 32 7 . 12 15 18 20 23 51 W 5 . 10 15 18 20 22 24 6 11 15 18 20 22 23 7 12 15 18 20 . 21 22 36 145 159 74 8 88 7 17 149 193 119 12 12 12 8 15 122 197 150 20 15 15 North 9 18 71 171 159 49 18 18 10 20 : 26 120 153 81 20 20 20 20 57. 119 103 30 20 12 N 21 21 21 74 111 74 21 N NW .. w $w S SE * Vetoes is bold taco are (or boon when aun is striking fenestration. t Value* for morning boon most be selected by reading dnm> far the proper direction Gated et toe toper the ooteBUt*. * Value* for afteraeon hours must be selected by reading p for the proper direction listed at the Mba of the enhimns. NW : - Horn 5 20 10 74 16 .140 18 201 20 243 22 267 24 276 6 . 29 11 83 16 145 18 201 20 22 262 23 270 7 40 12 91 16 148 18 198 20 231 21 255 22 .262 8 50 12 97 15 148 18 191 20 20 242 21 249 NE Horn Sun Time" 6 p.m. 5 pjn. 4 3 2 1 12 N 6 p.m. 5 4 3 2 1 12 N 6 p.m. 5 4 3 2 1 12 N 6 p.m. 5 4 3 1 12 N . Table 12 .... Solar Heat Gain-Factors*--Btuh Per Square Foot--for.July 21 latitude 24 Deg 32 Deg 40 Deg North 48 Deg North Sun Time* AMi^ 7 8 9 10 11 12 N 7 8 .9 10 11 12 N TM 7 8 9 10 11 12 N 7 8 9 10 11 12 N ,N 25 32 25 19 20 23. 24 28 24 18 18 20 22 23 29 17 16 18 20 21 21 27 13 15 18 19 20 21 N: NE 87 157 160 130 82 37 24 106 154 146 107 57 24 23 120 148 131 86 36 22 22 130 142 115 65 22 20 21 ' NW .E 93 179 200 178 128 63 24 115 186 200 : 177 128 62 23 135 190 200 176 - 126 - 60 22 149 192 200 . 175 123 59 21 - w. SE 39 90 IIS 111 90 54 26 52 104 - 131 134 116 81 39 63 111 145 154 140 107 '. 61 75 126 160 172 162 133 86 SW S 4 10 13 18 ' 21 25 29 5 11 15 22 36 48 52 6 11 . 18 38 65 84 91 7 11 ' 25 . 60 96 119 ' 128 S SW w` NW Horiz 44 10 10 15 15 18 IS 21 21 23 23 26 24 4 16 10 69 16 137 18 198 21 242 23 270 24 279 5 5 5 ; 23 11 11 11 76 15 15 15 140 18 18 18 196 20 20 20 236 22 22 22 261 39 23 . 23 . 270 6 6 6 . 31 11 11 11 82 15 15 15 140 18 18 18 190 20 20 20 227 25 21 21 251 61 22 22 258 7 7 7 39 11 12 12 86 15 15 15 137 18 18 18 182 19 19 19 215 36 20 20 235 86 21 21 . 242 SE - NE Horiz . Values in bold face awfor hoars when sun is striking feaesfeetioa. - - - ____ ' * Values ler.montatg boor* must be selected by nuiflng dawn foe tbs proper direction listed et the top eftho columns. - * Vetnri fnr njTniiim'Timin imiil In m lie till nr maitini iiji fill Ihn prnpnr rfirnstinn lintart et thn I rff*~ *w~ 1 ~ Sun Tfane* 6 p.m. 5 4 3 2 1 12 N 6 pjn. 5 4 3 2 1 12 N 6 p.m. 5 4 3 2 1 12 N 6 p.m. 5 4' 3. 2 1 12 N -TPM