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Heating a house with a furnace

  1. Feb 16, 2014 #1

    Maylis

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    Gold Member

    1. The problem statement, all variables and given/known data
    Consider the heating of a house by a furnace, which serves as a heat-source reservoir at a
    high temperature TF. The house acts as a heat sink at temperature T, and heat |Q| must be
    added to the house to maintain this temperature. Heat |Q| can of course be transferred
    directly from the furnace to the house, as is common practice. However, a third heat
    reservoir is readily available, namely, the surroundings at temperature T ., which can
    serve as another heat source, thus reducing the heat required from the furnace. Given that
    TF = 810 K, T = 295 K, Tσ = 265 K. and |Q| = 1,000 kJ, determine the minimum amount
    of heat |QF| which must be extracted from the heat-source reservoir (furnace) at TF . No
    other sources of energy are available.


    2. Relevant equations



    3. The attempt at a solution
    I am not sure if the way I am interpreting the question is right. There are some seemingly obvious mistakes, such as saying that the outside temperature helps reduce the amount of heat needed by the furnace.
     

    Attached Files:

  2. jcsd
  3. Feb 16, 2014 #2
    When a refrigerator works, heat is transferred from its colder internals to its warmer surroundings, so such transfer is not impossible.
     
  4. Feb 16, 2014 #3

    CWatters

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    I agree the problem statement isn't at all clear.

    It talks about the heat needed to "maintain" the temperature of the house. Normally that would suggest we are talking about power flows (eg to maintain a temperature the power flowing into and out of the house must sum to zero). However it states that the "heat" required is "1,000 kJ" which is energy not power.

    It sounds like they are trying to get you to apply Carnot.
     
  5. Feb 16, 2014 #4

    Maylis

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    Gold Member

    Yes, did I apply carnot correctly?
     
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