Solving Heat Pump Problem: 1/W = 1/(1-5/20)

[phoenix133231]

Homework Statement

If the temperature underground is 5 degrees Celsius and you'd like to keep the house at 20 degrees Celsius, how much work per joule leakage must be done to maintain the house at that temperature?

Homework Equations

Q/W = 1/(1-(Tc/Th))

The Attempt at a Solution

I know this may be wrong... but since I needed to know the work "per joule" leakage, I assumed that Q = 1 Joule. Then, I plugged in the terms into the formula provided and ended up with the following:

1/W = 1/(1-5/20)

which gave me W = 4/3 Joules. I checked the back of the book and the answer ended up being 0.05 Joules.

Could someone please provide me some understanding to this problem, as well as a hint on how to start? Is the formula provided even useful?

 

[iceworm]

Homework Statement

If the temperature underground is 5 degrees Celsius and you'd like to keep the house at 20 degrees Celsius, how much work per joule leakage must be done to maintain the house at that temperature?

Homework Equations

Q/W = 1/(1-(Tc/Th))

The Attempt at a Solution

I know this may be wrong... but since I needed to know the work "per joule" leakage, I assumed that Q = 1 Joule. Then, I plugged in the terms into the formula provided and ended up with the following:

1/W = 1/(1-5/20)

which gave me W = 4/3 Joules. I checked the back of the book and the answer ended up being 0.05 Joules.

Could someone please provide me some understanding to this problem, as well as a hint on how to start? Is the formula provided even useful?

Consider if you need to use absolute temperatures - degK.

ice

 

[phoenix133231]

LOL. I'm such a noob. That was exactly the problem. Thanks a lot!