  The air source heat pump (ASHP) systems assisted by solar energy have drawn
great attentions, owing to their great feasibility in buildings for space
heating/cooling and hot water purposes. However, there are a variety of
configurations, parameters and performance criteria of solar assisted ASHP
systems, leading to a major inconsistency that increase the degree of
complexity to compare and implement different systems. A comparative literature
review is lacking, with the aim to evaluate the performance of various ASHP
systems from three main solar sources, such as solar thermal (ST), photovoltaic
(PV) and hybrid photovoltaic/thermal (PV/T). This paper thus conducts a
systematic review of the prevailing solar assisted ASHP systems, including
their boundary conditions, system configurations, performance indicators,
research methodologies and system performance. The comparison result indicates
that PV-ASHP system has the best techno-economic performance, which performs
best in average with coefficient of performance (COP) of around 3.75, but with
moderate cost and payback time. While ST-ASHP and PV/T-ASHP systems have lower
performance with mean COP of 2.90 and 3.03, respectively. Moreover, PV/T-ASHP
system has the highest cost and longest payback time, while ST-ASHP has the
lowest ones. Future research are discussed from aspects of methodologies,
system optimization and standard evaluation.
