Dynamic performance of a novel solar photovoltaic/loop-heat-pipe heat pump system

Objective of the paper is to present an investigation into the dynamic performance of a novel solar photovoltaic/loop-heat-pipe (PV/LHP) heat pump system for potential use in space heating or hot water generation. The methods used include theoretical computer simulation, experimental verification, analysis and comparison. The fundamental equations governing the transient processes of solar transmission, heat transfer, fluid flow and photovoltaic (PV) power generation were appropriately integrated to address the energy balances occurring in different parts of the system, e.g., glazing cover, PV cells, fin sheet, loop heat pipe, heat pump cycle and water tank. A dedicated computer model was developed to resolve the above grouping equations and consequently predict the system's dynamic performance. An experimental rig was constructed and operated under the real weather conditions for over one week in Shanghai to evaluate the system living performance, which was undertaken by measurement of various operational parameters, e.g., solar radiation, photovoltaic power generation, temperatures and heat pump compressor consumption. On the basis of the first- (energetic) and second- (exergetic) thermodynamic laws, an overall evaluation approach was proposed and applied to conduct both quantitative and qualitative analysis of the PV/LHP module's efficiency, which involved use of the basic thermal performance coefficient (COPth) and the advanced performance coefficient (COPPV/T) of such a system. Moreover, a simple comparison between the PV/LHP heat-pump system and conventional solar/air energy systems was conducted. The research results indicated that under the testing outdoor conditions, the mean daily electrical, thermal and overall energetic and exergetic efficiencies of the PV/LHP module were 9.13%, 39.25%, 48.37% and 15.02% respectively, and the average values of COPth and COPPV/T were 5.51 and 8.71. The PV/LHP module was found to achieve 3-5% higher solar exergetic efficiency than standard PV systems and about 7% higher overall solar energetic efficiency than the independent solar collector. Compared to the conventional solar/air heat pump systems, the PV/LHP heat pump system could achieve a COP figure that is around 1.5-4 times that for the conventional systems. It is concluded that the computer model is able to achieve a reasonable accuracy in predicting the system's dynamic performance. The PV/LHP heat pump system is able to harvest significant amount of solar heat and electricity, thus enabling achieving enhanced solar thermal and electrical efficiencies. All these indicate a positive implication that the proposed system has potential to be developed into a high performance PV/T technology that can contribute to significant fossil fuel energy saving and carbon emission.