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Consider the composite wall of Problem 313 under conditions for which the inside air is still characterized by However use the more realistic conditions for which the outside air is characterized

Consider the composite wall of Problem 3.13 under conditions for which the inside air is still characterized by  However, use the more realistic conditions for which the outside air is characterized by a diurnal (time) varying temperature of the form

 

with ho = 60 W/m2 ∙ K. Assuming quasi-steady conditions for which changes in energy storage within the wall may be neglected, estimate the daily heat loss through the wall if its total surface area is 200 m2.

Problem 3.13

A house has a composite wall of wood, fiberglass insulation, and plaster board, as indicated in the sketch. On a cold winter day, the convection heat transfer coefficients are ho = 60 W/m2 ∙ K and hi = 30 W/m2 ∙ K. The total wall surface area is 350 m2.

(a) Determine a symbolic expression for the total thermal resistance of the wall, including inside and outside convection effects for the prescribed conditions.

(b) Determine the total heat loss through the wall.

(c) If the wind were blowing violently, raising ho to 300 W/m2 ∙ K, determine the percentage increase in the heat loss.

(d) What is the controlling resistance that determines the amount of heat flow through the wall?

Jun 28 2020 View more View Less

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