1. Briefly describe what is meant by “surface film” resistance and why the inter
ID: 234684 • Letter: 1
Question
1. Briefly describe what is meant by “surface film” resistance and why the interior surface film value is different from the exterior surface value.
2. Explain for different glazing types what the term “shading coefficient” means? What are typical shading coefficients commonly found for: • Single pane clear glass • Single pane tinted glass • Single pane reflective glass • Dual pane tinted outside/clear inside • Dual pane reflective outside/clear inside
3. A 200 square foot composite building wall is comprised of the following components: • 30% windows; U value = 1.06; SC = 0.70 • 20% hollow wood door; U = 0.46 • 50% wall; wall is constructed of 6” lightweight concrete (resistance of 0.60 per inch of thickness) and R-11 insulation. (Don’t forget to add surface film resistances!!) If the inside temperature is desired to be maintained at 70F and the outside temperature is15F; what is the heat transfer in Btu/hr for each component of the wall? What is the heat transfer for the entire wall?
4. What happens to the overall wall heat transfer rate if: • Solid core doors are used; U = 0.23 • Double pane windows are used with overall U = 0.53
Explanation / Answer
1. Surface film resistance is the material's inherent property to resist current flow. The value of interior to exterior varies due to to the varied effective forces acting upon the surfaces. on the outside, the inward-pulling force acts whereas in the inside the pressure acting outward keeps the surface intact.
2. Shading coefficient, is a value that determines one type of thermal performance of a glass unit (panel or window) in a building. it is the ratio of solar gain (due to direct sunlight) passing through a glass unit to the solar energy which passes through 3mm Clear Float Glass. It is referred to as an indicator to how the glass is thermally insulating (shading) the interior when there is direct sunlight on the panel or window. The shading coefficient (SC) depends on the color of glass and degree of reflectivity.
Single pane clear glass Single pane tinted glass Single pane reflective glass Dual pane tinted outside/clear inside Dual pane reflective outside/clear inside Shading Coefficient 0.82 0.59 0.26 0.48 0.20Related Questions
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