Research on energy-saving operating characteristics of water storage groundwater source heat pump heating system in plant factory

Abstract: The groundwater source heat pump has high efficiency and environmental protection in greenhouse temperature control. The operating energy consumption can be further reduced if the water storage technology were combined. It was researched which energy-saving operating characteristics a water storage groundwater source heat pump heating system has in this study, taking the example of the natural light plant factory in Shanghai. The total area was 21 000 m2, of which the heating area was 5 880 m2. The heating system included a groundwater heat exchange system, a heat pump unit, an air handling unit, and an energy storage system. Considering the change in electricity price and the change in heat load over time, the operating mode of the heating system is intermittent operation. At the time of power trough, the heat pump unit was fully open and energy was stored in the tank while heating. At the peak of power, the heat pump unit was stopped and the system made full use of the hot water tank for heating. At the time of the level section, reasonable regulation was carried out according to the stored energy of the hot water storage tank and the plant heat load demanded. The typical operating week，February 8th to 15th in 2017，was selected from the winter heating months. The operation data of the typical week was recorded and analyzed. The outdoor temperature，the solar radiation intensity，the indoor temperature，the indoor relative humidity and the COP(ratio of heat supply to power consumption) of the heat pump were all tested every 5 minutes on the typical week. The result shows that in winter, the groundwater source heat pump with energy storage tank heating system could better maintain the indoor temperature between 17 and 26 ℃. The indoor temperature was relatively low at night, but it could meet the growth demand of the crop at winter. The influence of solar radiation was large, and the indoor temperature was basically above 22 ℃, and even reached 28 ℃. The indoor relative humidity was always between 60% and 88%, which could avoid indoor high temperature with high humidity. When the system was in stable operation, the heat pump unit COP（coefficient of performance）was about 4.2. The day of February 9th, 2017 was selected from the typical week. On the typical day，it was cloudy and the temperature was below 4 ℃ throughout the day; the solar radiation intensity was 0-160 W/m2 and the average solar radiation intensity was 62 W/m2. The total power consumption of the system was 10 142.71 MJ, and the COP of the system was 3.17. It was further explained for the system characteristics of high efficiency and good stability. Compared with non-storage ground source heat pump system，the groundwater source heat pump with water energy storage system saved 30.34% of the cost on the typical day. The significant economic benefit of the test system was showed. During the continuous heating period in winter, for the test heating system, the primary energy utilization coefficient was 0.99. And compared with cold water unit and coal-fired boiler supporting system and chiller and gas boiler supporting system, energy saving rate were respectively 81.05% and 74.83%. Different energy heating costs were compared. For the operating cost, the coal, gas and fuel methods are 1.25, 2.93 and 5.08 times of the test heating system. And for the CO2 emission, they were 2.32, 1.19, and 0.88 times of the test heating system. Practice shows that the groundwater source heat pump with water energy storage system has good economic and environmental benefit, which can not only reduce the operating costs, but also make full use of geothermal energy and be beneficial to energy conservation.