System design and energy performance of a solar heat pump heating system with dual-tank latent heat storage

• The daily average collection efficiency η is proposed in the paper.
• A combination of COP and η is proposed to assess the energy efficiency of SHPHS.
• SHPHS–DLHS stores more thermal energy if we choose perfect operation strategy.

Thermal energy storage is widely regarded as one of the most promising technologies for ensuring that solar applications provide maximum energy efficiency and reliable energy supply. Phase-change materials (PCMs) can store latent heat energy during the phase-change process. The main objective of this study is to illustrate the energy-efficiency benefits of dual-tank latent heat storage (DLHS) installed in a solar heat-pump heating system (SHPHS). We designed and constructed an SHPHS–DLHS and tested it in the meteorological conditions of Beijing, China. As a result of this research, we defined a new performance parameter, the daily average collection efficiency (η). This parameter, combined with coefficient of performance (COP), can be used to evaluate the design of PCM thermal storage system and to maximize the use of the thermal storage media. We also tested thermal efficiency under different conditions and found that collection efficiency increases by up to 50% with the use of latent heat storage. The peak COP of the SHPHS–DLHS system was 10.03, roughly 3.5 times higher than that of the system using sensible heat water storage only. We conclude that PCMs improve an SHPHS system's energy efficiency.