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/m'2. 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?

Transcribed Image Text:

Glass fiber blanket (28 kg/m'), kg Plaster board, k, - Plywood siding, k, Outside Inside h T -15°C h, T- 20°C 11 11 10 mm - -100 mm- L, 20 mm