Saturday
October 25, 2014

Homework Help: College Physics

Posted by Becky on Saturday, October 8, 2011 at 12:28am.

In this problem you will estimate the heat lost by a typical house, assuming that the temperature inside is T(in) = 20 degrees celcius and the temperature outside is T(out) = 0 degrees celcius. The walls have fiberglass insulation, which dominates the heat conduction properties of the wall So we can consider the wall to have a thermal conductivity of k(wall) = 0.048 W/m/K
. We will take the thickness of the walls and ceiling to be L(wall) = 12 cm. Assume that the house is a cube of length L = 9.0 m on a side. Assume that the roof has very high conductivity, so that the air in the attic is at the same temperature as the outside air. Ignore heat loss through the ground.

a)What is H, the total rate of energy loss due to heat conduction for this house?

b)Let us assume that the winter consists of 150 days in which the outside temperature is 0*C on average. This will give the typical number of "heating degree days" observed in a winter in Vancouver. Given that heating oil has an energy content of 35 MJ per litre when burned, how much oil will be needed to supply the heat lost by conduction from this house over a winter? Assume that the heating system is 75% efficient.

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