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Consider we have water flowing in a pipe, which is working as a hot source for a heat pump. We are able to know the temperature of the water in both ends of the pipe, yet we don't have information about the temperature of it when it is in contact with the fluid in the heat pump. For me, in order to calculate the maximum achievable COP, it really seems resonable to consider the temperature of the hot source as the one of the water before passing by the heat pump. Would you agree? Or would it make more sense to average between the temperature at both ends of the pipe? I guess, there can be strange effects as far as heat conduction in fluids is concerned, so I wonder what would be the best decision.

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  • $\begingroup$ "it really seems resonable to consider the temperature of the hot source as the one of the water before passing by the heat pump. Would you agree?" yes. or maybe the mean temperature of the water that is is in contact with the coils or pipe of refrigerant of the heat pump. perhaps the mean of the two values of "temperature of the water [at] both ends of the pipe". $\endgroup$ Commented Mar 30, 2015 at 18:45
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    $\begingroup$ What are the consequences of picking the "wrong" answer? You will calculate a slightly different COP - but does that actually matter? Either approach is reasonable. $\endgroup$
    – Floris
    Commented Mar 30, 2015 at 19:34

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The maximum COP would be the water in the tube to be the same temperature of the body it's taking or giving energy to. When the heat transfer is 0 the maximum is reached.

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