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340 CHAPTER 13 1957 Guide LETTER SYMBOLS USED IN CHAPTER 13 a -- fraction of incident solar radiation absorbed, dimensionless; subscripts X), d, and t refer to direct, diffuse and total, respectively. (? = solar altitude, degrees. y = wall solar azimuth, degrees. t = emissivity, dimensionless. j ' 8 = incident angle, degrees. . X = amplitude decrement factor, dimensionless, r = fraction of incident solar radiation transmitted, dimensionless. Subscripts D, d and t refer to direct, diffuse and total, respectively. > <f> = solar azimuth, degrees. if/ = wall azimuth, degrees. A = area across which heat is being transferred, square feet. b = fraction of air passing through coil which does not contact surfaces, coil by-pass factor. f = unit surface conductance, Btu per (hour) (square foot) (Fahrenheit degree). Subscripts c, r, o, and i refer to convection, radiation, outdoor, and indoor, respectively. Gf = fraction of total window area receiving direct solar radiation when shaded by window reveal, dimensionless. h = enthalpy of air per pound of dry air, Btu per pound. Subscripts i, o, and s refer to indoor, outdoor, and supply air, respectively. 1 -- incident solar radiation, Btu per (hour) (square foot). Subscripts D, d, Dn, and t refer to direct, diffuse, direct normal and total solar radiation, respectively. K = cosine of angle of incidence for direct solar radiation striking a surface, dimen sionless. k = thermal conductivity of building material, Btu per (square foot) (hour) (Fahrenheit degree per inch). 1 = height of window, feet. M = the permeance of the specimen in perms or grains per (Bquare foot) (hour) (inch of mercury vapor pressure difference). Q -- rate of entry of outdoor air, cubic feet per minute. Qr = required air quantity through conditioning equipment, cubic feet per min ute. q = instantaneous rate of heat transfer, Btu per hour. q. = instantaneous latent heat load, Btu per hour, g.i = instantaneous space latent ventilation load, Btu per hour. gx = instantaneous latent ventilation load which does not become a part of space load, Btuh. gm = latent heat load due to moisture transmission through materials, Btu P& (hour) (square foot). q. = instantaneous sensible heat load, Btu per hour, g.i = instantaneous space sensible ventilation load, Btu per hour. q,, -- instantaneous sensible ventilation load which does not become a part of space load, Btu per hour. gi = g. + g., also g.i + g,, + g.i + gCI, Btu per hour. Rk = low temperature radiant energy received from outdoor surroundings (does not include solar radiation), Btu per (hour) (square foot of receiving surface). R = radiant energy emitted by a black body, Btu per (hour) (square foot)- Subscripts go and L refer to outdoor surfaces of glass and building, respeer tively. S = rate of heat storage within a glass section, Btu per (hour) (square foot). i. = sol-air temperature, Fahrenheit. Cooling Load 341 t* = sol-air temperature at a time earlier than the time for which heat gain is being found by an amount that is equal to the time lag of the wall or roof, Fatrenb-Sit, tgi -- temperature of indoor glass surface, Fahrenheit, fgo = temperature of outdoor glass surface, Fahrenheit. h -- indoor air temperature, Fahrenheit, in, =* 24-hr cyclic average sol-air temperature, Fahrenheit, io = outdoor air temperature, Fahrenheit, i, -- room supply air dry-bulb temperature, Fahrenheit. U = overall coefficient of heat transfer of a structural section, Btu per (square foot) (hour) (Fahrenheit degree). v0 -- volume of outdoor air per pound of dry air, cubic feet. w = width of window, feet. W = humidity ratio, pounds moisture per pound of dry air. Subscripts i, o, and s refer to indoor, outdoor, and supply air, respectively. REFERENCES 1 Application Engineering Standards for Air Conditioning for Comfort (Air Conditioning and Rcfrigcrat* ing Machinery Association, Inc., 1947, pp. 4-7). * Minimal Replenishment Air Required for Living Spaces, by W. V. Consolazio and L. J. Pecora (A.S.H.V.E. Transactions, Vol. 53, 1947, p. 127). * Safe Practice of the NBFU for Hospital Operating Rooms, Pamphlet No. 56, National Board of Fire Underwriters. 4 Proposed Standard SI<vt Radiation Curves for Engineering Use, by P. Moon (/ounutt of the Franldin Institute, November 1940, Vol. 230, No. 5, pp. 583-617). 1 AJ3.H.V.E. Research Report No. 1268--Summer Weather Data and Sol-Air Temperature--Study of Data for Linr^n, Nebr., by C. O. Mackey (A.S.H.VJ3. Tranbactions, Vol. 61,1945, p. 93). 1 Summer Weather Data and Sol-Air Temperature--Study of Data for New York City, by C. O. Mackey and E. B. Watson (A.S.H.V.E. Transactions, Vol. 51, 1945, p. 75). 18ommer Cooling for Comfort as Affected by Solar Radiation, by G. A. Hendrikson and J. H. Walkei (Heating and Ventilating, Vol. 29, No. 11, November 1932, pp. 14-21). Tables of Computed Altitude and Azimuth (U. 8. Navy Dept. Hydrographic Office Bulletin No. 214* Vole. 1-9, Washington, D. C., 1940). 'The American Nautical Almanac (U. S. Naval Observatory, Washington, D. C.t annual). " A.8.H.VJ5. Research Report No. 923--Heat Transmission as Influenced by Heat Capacity and Solar Radiation, by F. C. Houghten, J. L. Blackshaw, E. M. Pugh and Paul McDermott (A.S.H.V.E. Trans actions, Vol. 38, 1932, p. 231). Effect of Heat Storage and Variation in Outdoor Temperature and Solar Intensity on Heat Transfer Through Walls, by J. 8. Alford, J. E. Ryan and F. O. Urban (A.S.H.V.E. Trans actions, Vol. 45, 1939, p. 369). Periodic Heat Flow in Building Wall* Determined by Electrical An alogy Method, by Victor Paschkia (A.8 H.V E. Transactions, Vol. 48, 1942, p. 75).--Periodic Heat FlowHomogeneous Walls or Roofs, by C. O. Mackey and L. T. Wright, Jr. (A.S.H.VJL Transactions, Vol. 50. 1944, p. 293). Periodic Heat Flow--Composite Walls or Roofs, by C. O. Mackey and L. T. Wright, * (A.8.H.V.E. Transactions, VoL 52, 1946, p. 283). Periodic Heat Transfer at the Inner 8urface of a Homogeneous Wall, by H. A. Johnson (A.8.H.VH Transactions, Vol. 54, 1948, p. 143). u ThcEffectof SnluT HputTnmgmwnnn Through Walla, by F. C. Houghten, CarlGutberlet A* Hosenburg (American Society of Testing Materials Symposium on Thermal Insulating Materials, Philadelphia, 1939). A-8.H.V.E. Research Report No. 1157--Summer Cooling Load as Affected by Beat Gain Through Spnnkled and Water Covered Roofs, by F. C. Houghten, H. T. Olson and Carl Gutberlet (A.S.H.V.E. ANSIAACCTTIiOoNnbS. VVnoll. 14A6, i1f9ti4lr0t, -p. n23v7r\). Buildbi^" Heseabch Report No. 1002--Cooling Requirements of Single Rooms in a Modem Office p. 53)*' y C. Houghten, Carl Gutberlet, and Albert J. Wahl (A.S.H.V.E. Transactions, Vol. 41,1935 (A S h'v Actua* ** Predicted Cooling Load on An Air Conditioning System, by James N. Livermore 11 V*E* TaAN8ACTONB, Vol. 49, 1943, p. 287). ^^^rch Report No. 1195--Heat Gain Through Walls and Roofs as Affected by Solar VoL 4g ^ i^'.* 19, p. 91). Houghten, E. C. Hach, S. I. Taimuty and Carl Gutberlet (A.8.H.VJ5. TTrraannssaaccttions