Researchers in China have developed a new methodology to improve the performance of solar-powered air source heat pumps. The proposed approach reportedly increases the energy efficiency of optimized building systems by 18%, with solar energy potentially reducing their carbon content by 37.78%.
A group of researchers from China's Beijing University of Civil Engineering and Architecture has conceived a new control strategy for variable water temperature and variable flow in PV-driven heat pumps with the aim of increasing energy saving and system performance.
“We investigated the variable water temperature and variable flow rate of air source heat pumps (ASHPs) coupled with solar energy, including the coupling mode of solar PV and ASHPs, and the control optimization method of ASHPs,” the research's corresponding author, Xiaojun Wu, told pv magazine. “The study was conducted in laboratory buildings to determine the impact of energy conservation, carbon reduction, and coupling system performance.”
Their analysis considered an ASHP system consisting of the ASHP unit, a heat storage tank, and an end air conditioning box. Water circulates from the heat storage tank to the ASHP for heating or cooling and the treated water is then returned to the heat storage tank for later use. When needed, the treated water is sent via a water pump to the end air conditioner for room heating or cooling. In a further step, the cooled or heated water is sent to the storage tank and circulated back through the ASHP for further treatment.
This system was then configured in three different designs: 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 performance of the three systems was compared to that of a conventional ASHP system with a constant water temperature constant flow (CC-ASHP).
In the simulations, only the VV-ASHP 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.
The proposed control strategy was intended to be used mainly when the dynamic control of the building air conditioning system is weak and the photovoltaic energy is used less. Moreover, it demonstrated that the cooling and heating capacity of the four systems is able to cover the cooling and heating load requirements of building rooms.
The simulations showed 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%. Furthermore, the energy-saving efficiency of the VV-ASHP system was found to increase by 25.2 % and 20.6 %, respectively, in the cooling season and heating season.
VV-ASHP system was also found to have the highest seasonal energy efficiency ratio (SEER), heating seasonal performance factor (HSPF), and annual performance factor (APF), with values of 2.60, 3.65, and 2.99, respectively.
“Compared with the VV-ASHP system, CV-ASHP system, VC-ASHP system, and CC-ASHP system, the annual energy saving rate of the VV-ASHP system based on the solar coupling is increased by 18.0 %, 28.4 %, 29.3 %, and 37.8 %, respectively, which is more conducive to building energy conservation,” the scientists further explained.
They stressed that the proposed control strategy can help increase the energy efficiency of optimized building systems by 18%, with solar energy potentially reducing their carbon content by 37.78%.
Their findings can be found in the study “ASHP system based on a solar photovoltaic coupling study of a control strategy for variable water temperature and variable flow,” which was recently published in the Journal of Building Engineering.