Photovoltaic-ground-coupled heat pump system for farrowing pig house in different climate zones

More attention has been focused on the development and application of renewable energy all over the world, with the increasing concern for energy shortage and climate change. The large-scale pig farms can also be expected to extend the renewable energy. This study aims to meet the cooling/heating demand of a farrowing pig house in different building climate zones. A novel combination of Building Attached Photovoltaic (BAPV) systems and Ground-Coupled Heat Pump systems (GCHPs) was proposed to enhance the complementary effects of solar and geothermal energy, due to the difference in the cooling/heating load. Firstly, the borehole heat exchanger fields were optimized in the design of GCHPs, according to the cooling/heating load and ground thermal properties. Three cities were taken Suihua, Qingdao, and Chongqing located in the typical climate zones of severe cold areas, cold areas, and hot summer and cold winter zones. The result showed that a large difference was observed in the number of borehole heat exchangers for the farrowing pig house in the three cities, indicating the independence of BAPV systems. The ratio of heating and cooling load caused the different number of borehole heat exchangers, due to the limited inlet fluid temperature of a heat pump. Next, the Building Attached Photovoltaic-Ground-Coupled Heat Pump systems (BAPV-GCHPs) were modelled to investigate the system performance in the farrowing pig house located in different climate zones using Trnsys. The model was composed of a BAPV system, house load, and GCHPs. Electricity generation from the BAPV system were mainly supplied to the GCHPs, in order to expand the application of renewable energy in different climate zones. A comparison was made between the electricity generation and energy consumption. The potential of the two renewable energies was quantitatively investigated using the performance efficiencies in different operation periods. Finally, the presented system was compared with the operating performances in three climate zones, in order to clarify the effect of the BAPV system on the operating performance and comprehensive benefits of GCHPs. In the BAPV system, the power generation in Qingdao was the largest and followed by Suihua and Chongqing. The power consumption of GCHPs in Suihua was much higher than in the other cities. The annual solar factor of Suihua, Qingdao, and Chongqing were 0.62, 0.71, and 0.53, respectively. Additionally, the BAPV system contributed to the increased performance factors, the primary energy ratio, and CO₂ emission reductions for GCHPs. Compared with the GCHPs, the annual performance factors of BAPV-GCHPs in Suihua, Qingdao, and Chongqing were improved by 64.2%, 97.6%, and 39.6%, respectively. The BAPV-GCHPs system was more suitable for application in severe and cold areas than that in hot summer and cold winter zones. The primary energy ratio in Suihua, Qingdao, and Chongqing increased by 1.6, 2.4, and 1.1 times, respectively, whereas, the CO₂ emission was reduced by 5.82, 6.45, and 2.17 t, respectively. This trend was attributed to the BAPV contribution. This finding can provide a new pathway toward the application of renewable energy in farrowing pig houses, and then contribute to energy saving and carbon reduction in animal husbandry. The findings can provide strong references to promote and apply in different climatic zones in China.