An opportunity to combine air source heat pump (ASHP) technology with a renewable energy resource was explored by researchers in China. The variable water temperature and variable flow rate of these heat pumps, which harness the phase transition heat release of water for building heating systems, was tested with the integration of solar photovoltaics.

Three different configurations of a system consisting of the ASHP unit, a heat storage tank and an end air conditioning box were compared. The designs assessed formed an optimized ASHP system with constant water temperature variable flow (CV-ASHP); an ASHP unit with a variable water temperature constant flow (VC-ASHP); and a system integrating a variable temperature regulator consisting of a temperature sensor, a water temperature sensor and a temperature controller (VV-ASHP). The latter system was assumed to operate with the support of photovoltaic energy, with excess power being exported to the grid. During periods of low solar radiation, by contrast, the system can use grid electricity.

Simulations revealed that the annual energy-saving efficiency of the CV-ASHP system is 12.00%, the VC-ASHP system is 13.11% and the VV-ASHP system is 24.13%. The energy-saving efficiency of the solar-augmented system increased by 25.2% and 20.6%, respectively, in the cooling season and heating season.

The highest seasonal energy efficiency ratio of 2.60, heating seasonal performance factor of 3.65 and annual performance factor of 2.99 were also recorded for the solar-ASHP design. This strategy can help increase the energy efficiency of optimized building systems by 18%, with solar energy potentially reducing their carbon content by 37.78%.

The analysis conducted by scientists from Zhongkai University of Agriculture and Engineering and Beijing University of Civil Engineering and Architecture is published in the Journal of Building Engineering.