Document 44mBzLEVdzm763XJdOOw90D0G

American Society of Heating and Ventilating Engineers Guide, 1936 5__ Heat Transmission Coefficients and Tables 13 Table Coefficients of Transmission (tX) of Doors, Windows and Skylights j vciocity of IB mph. oni ore expressed in Bln per hour per square fool per fogcrenct in temperature between the air inside and outside of the door, window or skylight ----- " u Single.............. Double........... Triple............. Nominal Thickness Inches 1 iX iH IX 2 3 .................................. ............. B. Solid Wood Doorsb c Actual Thickness Inches J 2At lHe 1%6 m ia 2% 2A 1.13o.c 0.45 0.281 V 0.69 0.59 0.52 0.51 0.46 0.38 0.33 oec awitnti r -----------------------_. -- -- ------ w . _ ____ ________ _________________ `Computed using C = 1.15 for wood; fi 1.65 and/o 6.0. ' It is sufficiently accurate to_use the same coefficient of transmission for doors containing thin wood panels as that of single panes of glass, namely, 1.13 Btu per hour per square foot per degree difference between inside and outside air temperatures. 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 aluminum foil are given in Tabled. Coefficients of transmission of various types of wall, ceiling, floor and roof construction with aluminum insulation can be readily calculated.. The present installation practice indicates that air spaces of in. to 1 }/2 in. are preferred but 'manufacturers' recommendations 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 conductivifies 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). x Standard Test Code for Heat Transmission through Walls (A.S.H.V.E. Transactions, Vol. 34, 1928). See also Chapter 43.