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The COP of a heat pump operating between 6°C and 37°C will be:

  • A.8
  • B.10
  • C.12
  • D.14

Answer: B

The COP is 10.

For a reversible heat pump, with temperatures in kelvin, \(T_{H} = 37 + 273 = 310\) K and \(T_{L} = 6 + 273 = 279\) K:

\[ \begin{aligned} COP_{HP} &= \frac{T_{H}}{T_{H} - T_{L}} \\ &= \frac{310}{31} = 10 \end{aligned} \]

Using the refrigerator formula \(T_{L}/(T_{H} - T_{L}) = 279/31 = 9\) gives one less, because \(COP_{HP} = COP_{R} + 1\). Using degrees Celsius instead of kelvin gives nonsense values. 8, 12 and 14 do not come from the correct temperatures.

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