Question

Which of the following two windows would insulate better, and by how many times lower would the
rate of thermal conduction through it be compared to the other? Take both to be airtight and ignore
radiative losses. Each window has a total size of 1.2 m high by 0.6 m wide, with the outer 2 cm edge of
each window being the frame. For simplicity, take the frames to have the same thickness as the
glass. For the first window, let the frame be solid wood with a thermal conductivity of 0.1 W/(m*K), and
the pane is solid glass with a thermal conductivity of 0.8 W/(m*K). For the second window, let the
frame be two thin pieces of steel (each 1/10 of the total thickness), with an air gap in between. The
steel has a thermal conductivity of 50 W/(m*K), and air has a thermal conductivity of 0.025
W/(m*K). The pane is made of two thin layers of glass (each 1/3 of the total thickness), with an air gap
in between. The glass used is the same type as that used in the first window.

Answer 1

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