Investigations and model validation of a ground-coupled heat pump for the combination with solar collectors

• A brine/water heat pump was tested under steady-state and transient conditions.
• Decline of exergetic efficiency at low temperature lifts, no influence of flow rate.
• Expected improvement by reciprocating compressor and electronic expansion valve for solar assisted heat source.
• A TRNSYS black box model (YUM) was validated and a flow rate correction was proven
• The start-up behavior is a very important parameter for system simulations.

The operation of ground-coupled heat pumps in combination with solar collectors requires comprising knowledge of the heat pump behavior under non-standard conditions. Especially higher temperatures and varying flow rates in comparison to non-solar systems have to be taken into account. Furthermore the dynamic behavior becomes more important.At ISFH, steady-state and dynamic tests of a typical brine/water heat pump have been carried out in order to analyze its behavior under varying operation conditions. It has been shown, that rising source temperatures do only significantly increase the coefficient of performance (COP), if the source temperature is below 10–20 °C, depending on the temperature lift between source and sink. The flow rate, which has been varied both on the source and the sink side, only showed a minor influence on the exergetic efficiency. Additionally a heat pump model for TRNSYS has been validated under non-standard conditions. The results are assessed by means of TRNSYS simulations.