Question: A window consists of two layers of glass, each 1/4 in. thick, separated by a layer of dry, stagnant air, also 1/4 in. thick. If the outside surface to inside surface temperature drop over the composite system is 30°F, find the heat loss through such a window that is 10 ft wide and 4 ft high
The window is proposed to replace a single glass pane, 3/8 in. thick, at a difference in cost of $120.
The thermal conductivity of the window glass is 0.5 Btu/@ ft OF). Fuel costs $0.75 per million Btu combustion energy obtained. The furnace efficiency can be assumed to be 60 percent. Find the number of days of operation under the specified temperature conditions to pay for the window. Determine the sensitivity of the number of days to the price of fuel. Is the assumption of stagnant air a good one?