부산대학교 도서관

Energy consumption in greenhouse accounts for about 40-50% of the total production cost in many countries. Saving energy and reducing greenhouse gas emissions (GHG) in the food supply chain are part of the sustainable development goals to reduce the bottlenecks in the agricultural energy-sector. Several countries have made concerted effort for the improvement of greenhouse efficiency by replacing the traditional carbon-based energy systems with heat pump systems (HPS). The South Korean government has planned to key into this policy by proposing a reduction of GHG to 18.1% by 2030 and completely neutralizing it by 2050, through continuous application of HPS in the energy-consuming sector. This study, through experimental investigation, analyzes the performance of six integrated HPS installed at Yeoju-si, Gyeonggi-do, western South Korea. The HPS use night thermal energy storage (NTES) as a buffer and tube rails and fan coil units as terminal units to supply hot water to the greenhouse. Two of the HPS are ground source heat pumps (GSHP) while others are hybrid heat pumps (HHP) using air as air source heat pump (ASHP) and evaporative heat source from tank thermal energy storage (TTES) and borehole thermal energy storage (BTES). The average monthly coefficient of performance (COP) of the ASHP varies between 0.94 - 2.32. It has the lowest value of 0.94 due to defrosting operation in January when the mean monthly temperature was -3.6 ℃. The GSHP has the highest COP ranging from 3.24 - 3.84, then HHP using heat source from BTES, 1.84 - 2.84 and TTES, 1.17 - 2.68. During the investigation, at least 50 ℃ water temperature was maintained in the NTES. In extreme low weather conditions, electric boiler installed between the NTES and the greenhouse increases the inlet tube water temperature to constant 55 ℃. The HPS configuration supplied 85% of the total energy consumed by the greenhouse in the coldest month, reducing the GHG that would have been emitted if the energy supply system was completely carbon-based. The terminal unit capacity compared with other tube emission standards was also sufficient to maintain the greenhouse internal temperature and is recommended for future use and further study.