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Homework Help: Thermodynamics: Carnot efficiency

  1. Jan 18, 2009 #1
    1. The problem statement, all variables and given/known data

    In one location, the average daily temperature varies sinusoidally between 35C in summer and 0C in winter. The ground temperature below 2 m underground is the annual average temperature. A heat pump / air conditioner unit must deliver air to a house at 30C in winter and 15 C in summer. If the unit operates at 25% of Carnot efficiency, how much power is consumed per each kW of heating or cooling provided if the unit operates air source and ground source in winter and summer?

    2. Relevant equations

    How do i get Q for each case?

    3. The attempt at a solution

    Winter: efficiency n = 0.25(1 - 0/30) = 0.25
    Summer: n = 0.25(1 - 15/35) = 0.1429

    n = Q_hot/W_cycle, so we need Q_hot, where both W and Q are rates of work and heat transfer
  2. jcsd
  3. Jan 20, 2009 #2
    nevermind i figured it out
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