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198 CHAPTER 9 1953 Guide value of .1.65 used in computing U values given in other tables in this chapter. These values should therefore be used in estimating the tem perature at-which condensation on.glass surfaces will occur.' The application factors given in Section D of Table 20 are based upon hot box tests summarized in a research' biilletin16, and are approximate only. In practice, some variation in heat flow through windows having the same ratio of glass to sash area, may be expected because of difference in construction details and in'air space edge effects. ' CALCULATING SURFACE TEMPERATURES In many heating and cooling load calculations it is necessary to deter mine the inside surface temperature or the temperature of the surfaces within the structure. As the resistance of any path of heat flow is ex pressed in Fahrenheit degrees per (Btu) (hour) (square foot), the re sistances through any two paths of heat flow would be.proportional to the temperature drop through these paths, and can be expressed as follows: ft Ci - O ' ft = (7T^) ' (6) where ft = the resistance from the inside air to any point in the structure at which the temperature is to be determined. ft = the overall resistance of the wall from inside air to outside air. fi = inside air temperature. tx = temperature to be determined. f,, = outside air temperature. Example 2: Determine the inside surface temperature for a wall having an overall coefficient of heat transmission U = 0.25, inside air temperature 70 F, outside air temperature --20 F. - Solution: Then, by Equation 6 ft = l//i = 1/1.65 = 0.606 ft = 1/U = 1/0.25 = 4.00 0.606 70 - tx 4.00 = 70 - (-20) tx = 56.4 F The same procedure can be used for determining the temperature at any point within the structure. A chart for determining inside wall surface temperature is given in Fig. 12 of Chapter 24, Panel Heating. REFERENCES 1 Standard Method of Test for Thermal Conductivity by Means of the Guarded Hot Plate, sponsored by A.S.H.V.E., A.S.T.M., A.S.R.E., and N.R.C., and approved as a Tentative Code by A.S.H.V.E. and A.S.T.M. in 1942 (A.S.T.M. designation C-177-45, Approved 1945). * Heat Transmission Through Building Materials, by F. B. Rowley and A. B. Algren (University of Minnesota, Engineering Experiment Station Bulletin, No. 8, p:ll). Thermal Properties of Soils, by Miles S. Kersten (University of Minnesota, En gineering Experiment Station Bulletin No. 21, June 1949). Heat Transmission Coefficients of Building Materials 199 4 P_adiation and Convection from Surfaces in Various Positions, by G. B. Willies and C. M. F. Peterson (A.S.H.V.E. Transactions, Vol. 44, 1938, p. 513). Radiation Corrections for Basic Constants Used in the Design of All Types of Heating Systems, by B. F. Raber and F. W. Hutchinson (A.S.H.V.E. Transactions, Vol. 51, 1945, p. 213). A.S.H.V.E. Research Report No. 869--Surface Conductances as Affected by Air Velocity, Temperature and Character of Surface, by F. B. Rowley, A. B. Algren and J. L. Blackshaw (A.S.H.V.E. Transactions, Vol. 36, 1930; p. 444). . 7 Forced Convection Heat Transfer from Flat Surfaces, by G. V. Parmelee and R. G. Huebscher (A.S.H.V.E. Research Bulletin No. 3, p.,40; also published in A.S.H.V.E. Transactions, Vol. 53, 1947, p. 276). A.S.H.V.E. Research Report No. 1399--Heat Flow through Unshaded Glass: Design Data for Load Calculations, by G. V. Parmelee and W. W. Aubele (A.S.H.V.E. Transactions, Vol. 56, 1950, p. 371). Radiation and Convection Across Air Spaces in Frame Construction, by G. B. Wilkes and C. M. F. Peterson (A.S.H.V.E. Transactions, Vol. 43, 1937, p. 351). 10 Thermal Test Coefficients of Aluminum Insulation for Buildings, by G: B. Wilkes, F. G. Hechler and E. R. Queer (A.S.H.V.E. Transactions, Vol. 46, 1940, p. 109). 11 Effect of Studs and Joists on Heat Flow Through Frame Walls and Ceilings, by Paul D. Close (Healing, Piping and Air Conditioning, October, 1943, p. 529). 17 A.S.H.V.E. Research Report No. 1213--Heat Loss ThrougTi Basement Walls and Floors, by F. C. Houghten, S. I. Taimuty, Carl Gutberlet and C. J. Brown (A.S.H.V.E. Transactions, Vol. 48, 1942, p. 369). * Measurements of Heat Losses from Slab Floors, by R. S. Dill, Wm. C. Robinson and H. E. Robinson (National Bureau of Standards, Building Materials and Structures Report BMS 103). 14 See pp. 130-132 of Reference 7. 16 Heat Transmission through Glass, by G. V. Parmelee (A.S.H.V.E. Research Bulletin No. 1, July 1947). BIBLIOGRAPHY A.S.H.V.E. Research Reports: No. 852--Effects of Air Velocities on Surface Coefficients, by F. B. Rowley, A. B. Algren and J. L. Blackshaw (A.S.H.V.E. Transactions, Vol. 36, 1930, p. 123). No. 895--Wind Velocity Gradients Near a Surface and Their Effect on Film Conductance, by F. C. Houghten and Paul McDermott (A.S.H.V.E. Transactions, Vol. 37, 1931, p. 301). No. 914--Surface Coefficients as Affected by Direction of Wind, by F. B. Rowley and W. A. Eckley (A.S.H.V.E. Transactions, Vol. 38,1932, p. 33). No. 915--Conductivity of Concrete, by F. C. Houghten and Carl Gutberlet (A.S.H.V.E. Transactions, Vol. 38, 1932, p. 47). No. 964--Tin: Heat Conductivity of Wood at Climatic Temperature Differences, by F. B. Rowley (A.S.H.V.E. Transactions, Vol. 39, 1933, p. 329). No. 996--Insulating Value of Bright Metallic Surfaces, by F. B. Rowley (A.S.H.V.E. Transactions, Vol. 40, 1934, p. 413). No. 1026--Thermal Properties of Concrete Construction, by F. B. Rowley, A. B. Algren and Clifford Carlson (A.S.H.V.E. Transactions, Vol. 42, 1936, p. 33). No. 1048--Thermal Properties of Concrete Construction, by F. B. Rowley, A- B. Algren and Robert Lander (A.S.H.V.E. Transactions, Vol. 43> 1937, p. 33). A.S.H.V.E. Research Report No. 1351--Overall Coefficients for Flat Glass De termined under Natural Weather Conditions, by G. V. Parmelee and W. W. Aubele (A.S.H.V.E. Transactions, Vol. 55, 1949, p. 39). Insulating Effect of Successive Air Space Bounded by Bright Metallic Surfaces, by L. W. Schad (A.S.H.V.E. Transactions, Vol. 37, 1931, p. 285). Thermal Conductivity of Wood, by J. D. MacLean (A.S.H.V.E. Transactions, Vol. 47, 1941, p. 323). The Specific Heat of Thermal Insulating Materials, by G. B. Wilkes and C. O. Wood (A.S.H.V.E. Transactions, Vol. 48, 1942, p. 493).