Document 6BYGq2dk0jgzvDEN5dqOgpJR1

American Society of Heating and Ventilating Engineers Guide, iqjj 112 -Heat Transmission Coefficients and Tables 13 TABLE Coefficients of Transmission (U) of Doors, Windows and Skylights on a wind velocity of 16 mph, and are expressed in Bln per hour per square fool per faitdiffcrence in temperature between the air inside and outside of'the door, window or skylight A . Windows and Skylights u Single--....... --- ----------- --- -- Triple-......... -..... -.......... -------------- B. Solid Wood Doors1'-c ) Nominal Tskxnmb Inch*a 1 lM 1H isA 2 2X 3. .. Actual Thickness Inches IXe m m 2X - 2y8 v \ 1.130, c 0.45 0.281 UV ' 0.69 0.59 0.52 0.51. 0.46 0 38 0.33 ' - n eating, r ****<*/# ** ** * ^Computed using C *> 1.15 for wood;/i'= 1.65 arid/o '*. 6.0. ', v*v, It is sufficiently accurate to use the same coefficient of transmission for doors containing t ,,,,i- . that nf single Danes of,glass, namely. 1-13 Btu per hourpersouare foot per degree < While most building materials have surfaces which show similar characteristics as far as the transmission of heat is concerned, it is a wellknown fact that certain surfaces such as aluminum bronze, gold bronze, aluminum foil, or in fact any metallic, highly polished surface presents a greater resistance to heat transmission than the surface of the average building material. The greater, heat resistance of such: metallic surfaces is due.primarily to their higher reflectivity and consequent lower emissivity of radiant heat. The use of multiple layers of metallic surfaces, combined with air spaces of low resistance, provides'a definite insulating effect. -Factors2 for air spaces bounded by aluminurh;fpii are;given in Table 2. Coefficients of. transmission of various types of wall, ceiling, floor and roof construction with aluminum insulation can be readily calculated. The present installation1 practice indicates that air spaces of l/i in. to 1 Vi in. are preferred but manufacturers', recommendatidns should be closely followed in the application of aluminum foil insulation. The majority of the conductivities and conductances of the building, materials and insulations given in Table 2 were determined by the hot plate method of testing3. Attention is called to the fact that conductivi ties per inch of thickness of materials or insulations do not afford a true basis for comparison, although they are frequently used for that.purpose. `Insulating Value of Bright Metallic Surfaces, by F. B. Rowley (A.S.H.V.E. Journal Section, Heating, Piping and Air Conditioning, June, 1934, p. 263). Standard-Test Code See also Chapter 40. for Heat Transmission through Walls (A.S.H.V.E. Transactions, Vol. 34, 1928). 113