In some countries (e.g., South Africa), important market areas for air-source heat pumps are situated high above sea level, and it is therefore necessary to know what the influence of height is on the performance of heat pumps for water healing. Therefore, a study was conducted that predicts the influence of height on the coefficient of performance (COP) of air-source heat pumps. An expression was derived that gives the heat transfer to the evaporator of a heat pump as a junction of air density and enthalpy as well as the outside heat transfer coefficient. This expression was used to predict the influence of height above sea level on COP. The results were verified by means of a simulation study. It was concluded that height has little influence on COP if the evaporator of the heat pump is wet on the air side. A more significant weakening in the performance occurs, however, when the air side of the evaporator is dry.
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