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Energy heating a home?

  1. Feb 26, 2009 #1
    energy heating a home???

    1. The problem statement, all variables and given/known data
    During 2 hours one winter afternoon, when the outside temperature was 4° C, a house heated by electricity was kept at 20° C with the expenditure of 42 kwh (kilowatt·hours) of electric energy.

    (a) What was the average energy leakage in joules per second (watts) through the walls of the house to the environment (the outside air and ground)?
    in watts

    (b) The rate at which energy is transferred between two systems due to a temperature difference is often proportional to their temperature difference. Assuming this to hold in this case, if the house temperature had been kept at 24° C (77° F), how many kwh of electricity would have been consumed?
    in kwh

    2. Relevant equations
    only one i know is
    Cm(Tf - Ti) + Cm(Tf - Ti) = 0
    where C is specific heat capacity
    m is mass
    Tf is final temp
    Ti is inital temp

    3. The attempt at a solution
    was going to figure out final temp using above equation and then compare that to the final temp given. but dont know the C so got stuck.
  2. jcsd
  3. Feb 26, 2009 #2


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    Re: energy heating a home???

    Part a, how much energy went into the house, where did that energy go?
  4. Feb 26, 2009 #3
    Re: energy heating a home???

    it is an open system which means the energy is not conserved.
    i did conservation of energy but did not think it would be right
    because you are loosing energy through the walls which means
    you have to input more energy
  5. Feb 26, 2009 #4


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    Re: energy heating a home???

    Yes, the energy in all ends up going outside in the long term, so part a is simply asking how many joules were supplied during the 2 hours.
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