The thermal conductivity of fiberglass batting, which is 8.9 in thick, is 8.6 10-6 BTU/(ft °F s). What is the R value (in ft2 °F h/BTU)?
The R value is 24 ft^2 Fh/BTU. How do I get this answer?
R is the reciprocal of the amount of BTU of heat transfered across 1 ft^2 in 1 hour with a temperature difference of 1 F.
1/R = 8.6*10^-6*3600 s*(1.0 degF)/(8.9/12 ft)
R = 24 ft^2*degF*h/BTU
Thank you!
Could you write out just the basic equation that you used?
The equation I found in my text book doesn't mention time being a factor when calculating R.
I have R= L/k
where L is length and k is thermal conductivity.
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To calculate the R value, which represents the resistance to heat flow of a material, you can use the following formula:
R = Thickness / Thermal Conductivity
Given that the thickness of the fiberglass batting is 8.9 inches, you need to convert it to feet by dividing it by 12 (since there are 12 inches in a foot):
Thickness = 8.9 inches / 12 = 0.7417 feet
Now, you can substitute the values into the formula:
R = 0.7417 feet / (8.6 x 10^-6 BTU/(ft °F s))
To simplify the calculation, first convert the thermal conductivity from BTU/(ft °F s) to BTU/(ft °F h) by multiplying it by 3600 (since there are 3600 seconds in an hour):
Thermal Conductivity = 8.6 x 10^-6 BTU/(ft °F s) * 3600 s/h = 0.03096 BTU/(ft °F h)
Now substitute the values into the formula:
R = 0.7417 feet / 0.03096 BTU/(ft °F h)
Simplifying the equation gives:
R = 23.931 ft² °F h/BTU
And rounding to the nearest whole number, the R value is approximately:
R = 24 ft² °F h/BTU
So, the R value of the fiberglass batting is 24 ft² °F h/BTU.