Energy performance indexes for solar assisted ground source heat pump systems with photovoltaic-thermal collectors

Abstract Applications with photovoltaic thermal collectors (PVTs) are becoming popular due to their capability of cogenerating heat and power from the same surface. Solar assisted ground source heat pump (SAGSHP) systems are considered a potential solution for utilization of PVTs. Up to now, the seasonal performance factor (SPF) has been used by most of the existing literature to evaluate the energy performance of the PVT based SAGSHP systems. However, the PVTs coproduce heat and power, and the SPF omits the generated electricity and overlooks the influence of the system on the collectors’ electrical efficiency. Driven by the limitation of the SPF to illustrate the overall system’s energy performance, this study introduces a new improved energy performance metric. The study was carried out by varying the size of the PVT array and via the results six energy indexes were evaluated. The parametric analysis was conducted by a validated model formulated in TRNSYS. Based on the results, the renewable power fraction (RPF) was found as the most suitable index to assess the performance of PVT-SAGSHP system. A 7% reduction was estimated in the PVTs’ electricity generation, by choosing the higher SPF instead the higher RPF. The proposed RPF index overcomes restrictions of doing calculations with both electricity and heat at the same equation. Thus, the RPF is considered capable of indicating the overall energy performance of the systems, without limitations. Finally, the proposed metric (RPF) can be used to study the energy performance of any solar system equipped with PVTs.