Chapter 3 Steady Heat Conduction3-142 The winter R-value and the U-factor of a flat ceiling with an air space are to be determined for the cases of air space with reflective and nonreflective surfaces. Assumptions1 Steady operating conditions exist. 2Heat transfer through the ceiling is one-dimensional. 3 Thermal properties of the ceiling and the heat transfer coefficients are constant. PropertiesThe R-values are given in Table 3-6 for different materials, and in Table 3-9 for air layers. AnalysisThe schematic of the ceiling as well as the different elements used in its construction are shown below. Heat transfer through the air space and through the studs will meet different resistances, and thus we need to analyze the thermal resistance for each path separately. Once the unit thermal resistances and the U-factorsfor the air space and stud sections are available, the overall average thermal resistance for the entire wall can be determined from Roverall= 1/Uoverallwhere Uoverall= (Ufarea)
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