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Homework Help: Heat pump cycle

  1. Sep 19, 2004 #1
    Here's my problem:
    A heat pump cycle whose coefficient of performance is 2.5 delivers energy by heat transfer to a dwelling at a rate of 20 kW.
    a) Determine the net power required to operate the heat pump, in kW.
    b) Evaluating electricity at 8 cents per kWh, determine the cost of electricity in a month when the heat pump operates for 200 hours.

    I know that the coefficient of performance = Qout/Wcycle = Qout/(Qout-Qin).
    But what is meant by net power? And more importantly, how do I calculate it?

    Thanks for help in advance,
    eku_girl83
     
  2. jcsd
  3. Sep 20, 2004 #2

    russ_watters

    User Avatar

    Staff: Mentor

    Power to operate the heat pump is Qin.
     
  4. Sep 20, 2004 #3
    Here's my problem:
    A heat pump cycle whose coefficient of performance is 2.5 delivers energy by heat transfer to a dwelling at a rate of 20 kW.

    a) Determine the net power required to operate the heat pump, in kW.
    20 kw/2.5 = electrical power input = 8 kw This must be the "net power."
    That is about typical for a freon based heat pump. I got one.

    b) Evaluating electricity at 8 cents per kWh, determine the cost of electricity in a month when the heat pump operates for 200 hours.
    8 kw x 200 hr = 1600 kwh. 1600 kwh x .08 $/kwh = $128.00
    Looks like a typical bill to me. But natural gas is cheaper.

    I know that the coefficient of performance = Qout/Wcycle = Qout/(Qout-Qin).
    But what is meant by net power? And more importantly, how do I calculate it?
     
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