Transient model of a geothermal heat pump in cycling conditions – Part A: The model

A transient model of a water-to-air geothermal heat pump subjected to cycling operation is proposed in this paper. A distributed approach is used where each component is modeled individually and then linked into a so-called global model. The model can predict the state of the refrigerant throughout the circuit during normal operation and at compressor shut down where there may still be some small refrigerant flow. The governing equations of refrigerant and secondary fluid flows, along with tube wall temperatures evolutions, are solved using the finite volume method. The originality of the proposed model lies in its distributed approach which allows to capture both the on-cycle and the off-cycle, with fan on or off at compressor shut-down. Results presented in a companion paper show that the model is able to predict with relatively good agreement the measured transient behavior of a geothermal heat pump.