A thermal window consisting of two panes of 0.25" glass (R-value 0.08 hr · ft2. °F/BTU each), separated by a layer of air 0.75" thick is now used as a horizontal window in the ceiling (a skylight) of an air conditioned room. Find its R-value in the summer, when the outside is warmer than the inside, and in the winter, when the inside is warmer than the outside (in hr · ft2. °F/BTU). (Assume that the air is moving outside the window.) R (summer) _hr ft2. °F/BTU R (winter) hr ft2. °F/BTU

A thermal window consisting of two panes of 0.25" glass (R-value 0.08 hr · ft2. °F/BTU each), separated by a layer of air 0.75" thick is now used as a horizontal window in the ceiling (a skylight) of an air conditioned room. Find its R-value in the summer, when the outside is warmer than the inside, and in the winter, when the inside is warmer than the outside (in hr · ft2. °F/BTU). (Assume that the air is moving outside the window.) R (summer) _hr ft2. °F/BTU R (winter) hr ft2. °F/BTU

Elements Of Electromagnetics

7th Edition

ISBN:9780190698614

Author:Sadiku, Matthew N. O.

Publisher:Sadiku, Matthew N. O.

ChapterMA: Math Assessment

Section: Chapter Questions

Problem 1.1MA

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Concept explainers

Conduction and Convection

When energy travels from one object to another it is said to have undergone heat transfer. Heat transfer is nothing but the transfer of thermal energy or internal energy from one thing to another, like e.g., when a vessel with water, kept on top of a burner, heats up because of the flame underneath it.

Question

A thermal window consisting of two panes of 0.25"
glass (R-value 0.08 hr · ft2. °F/BTU each), separated
by a layer of air 0.75" thick is now used as a
horizontal window in the ceiling (a skylight) of an air
conditioned room. Find its R-value in the summer,
when the outside is warmer than the inside, and in
the winter, when the inside is warmer than the
outside (in hr . ft2. °F/BTU). (Assume that the air is
moving outside the window.)
R (summer)
hr · ft2. °F/BTU
R (winter)
hr : ft2 . °F/BTU

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Consider a double-paned window consisting of two panes of glass, each with a thickness of 0.500 cm and an area of 0.795 m2 , separated by a layer of air with a thickness of 1.50 cm. The temperature on one side of the window is 0.00 ∘C∘C; the temperature on the other side is 21.0 ∘C∘C. In addition, note that the thermal conductivity of glass is roughly 36 times greater than that of air. Approximate the heat transfer through this window by ignoring the glass. That is, calculate the heat flow per second through 1.50 cmcm of air with a temperature difference of 21.0 ∘C∘C. (The exact result for the complete window is 25.6 J/sJ/s .)
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