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23 Nov 2019

A homeowner has insulated a 1750ft2 attic with R30 insulation. The R value commonly used in home insulation has been defined so that R = x/k (thickness, (x), divided by conductivity, (k), in units of hr*ft2*oF/Btu). On a certain day, the inner temperature of the insulation is 65 oF and the outer temperature of the insulation is 30 oF. What is the heat loss through the attic insulation?

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Deanna Hettinger
Deanna HettingerLv2
17 May 2019

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Related textbook solutions

Physics: Principles with Applications
7th Edition, 2013
Giancoli
ISBN: 9780321625922

Related questions

In this problem you will estimate the heat lost by a typical house, assuming that the temperature inside is Tin = 20°C and the temperature outside is Tout = 0°C. The walls and uppermost ceiling of a typical house are supported by 2 × 6-inch wooden beams (kwood insulation (kins = 0.04 W/(mK)) in between. The true depth of the beams is actually 5.625 inches, but we will take the thickness of the walls and ceiling to be Lwall interior and exterior covering. 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. The effective thermal conductivity of the wall (or ceiling) keff , is the area-weighted average of the thermal conductivities of the wooden beams and the fiberglass insulation that make up each of them. Allowing for the fact that the 2 x 6 beams 0.12 W/(mK)) with fiberglass 18 cm to allow for the are actually only 1.625 inches wide and are spaced 16 inches center to center, a calculation of this conductivity for the walls yields keff that the ceiling also has the same value of keff - 0.048 W/(mK). How much heat per second (H = Q/ΔT) is lost from the house due to heat conduction?

 



In this problem you will estimate the heat lost by a typical house,assuming that the temperature inside is T(in) = 20*C and thetemperature outside is T(out) = 0*C. The walls have fiberglassinsulation, which dominates the heat conduction properties of thewall So we can consider the wall to have a thermal conductivity ofk(wall) = 0.048 W/m/K. We will take the thickness of the walls andceiling to be L(wall) = 12 cm. Assume that the house is a cube oflength L = 9.0 m on a side. Assume that the roof has very highconductivity, so that the air in the attic is at the sametemperature as the outside air. Ignore heat loss through theground.



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

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

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