The top-story ceiling of a building measures 30 by 45 ft. An unventilated attic

Question

The top-story ceiling of a building measures 30 by 45 ft. An unventilated attic is formed by a pitched roof which has an area 1.6 times the ceiling area. The ceiling U value is 0.09Btu /hr-ft^2-F, and the U value for the roof is 0.58 Btu/hr-ft^2-F. The air temperature below the roof is 78 degree F and the outside air temperature is 5 degree F. Find: The estimated attic temperature The ceiling-roof overall heat transmission coefficient based on ceiling area The heat loss from the building through the ceiling-roof construction in Btu/hr.

Explanation / Answer

a) Attic temperature is approximately equal to 78 F because the attic is unventilated.

b) 1 / hoverall   = 1 / 0.09 * 30 * 45    + 1 / (0.58 * 1.6 * 30 * 45)

      hoverall = 110.7583 BTU/hr F

c) Heat loss = hoverall * ( 78 - 5)   = 8085.36 BTU/hr

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