Study On Operation Strategy Of Water Intake Medium And Deep Geothermal System Combined With Shallow Ground Source Heat Pump System In Facility Agriculture

Since September 2020,when China clearly put forward the goal of achieving carbon peaking by 2030 and carbon neutrality by 2060,the development and utilization of new energy sources has become more and more urgent.Geothermal energy has abundant reserves in China.With the development of the times,China’s industrialization of protected agriculture has become more and more developed.In protected agriculture,supplemental temperature cooling and supplemental light are high-energy consumption measures,and protected agriculture has gradually become a high-energy consumption industry.Compared with boilers and air source heat pumps used in protected agriculture in the past,geothermal systems have the advantages of low operation and maintenance costs and environmental protection.The paper introduces a study on the application and optimization of control strategy for a water-taking type mediumdeep geothermal combined with shallow ground source heat pump system in protected agriculture.The object of this study is a water-intake type middle-deep geothermal combined shallow ground source heat pump system located in Yangling Intelligent Agriculture Demonstration Park in Shaanxi Province.The system consists of middle-deep geothermal system and shallow ground source heat pump system.The medium-deep geothermal system is composed of two primary heat exchanger plates,one secondary heat exchanger plate and a screw water source heat pump with rated power of 273.3k W,which provides heat supply for the tomato area of Venlo greenhouse.The shallow ground source heat pump system consists of two water source heat pumps with a rated power of 650 k W and two water chillers with a rated power of 614.4k W.It provides cooling and heating for the lettuce area,greenhouse and office area in Venlo greenhouse.The park has built two medium-deep geothermal Wells and 31 water-source heat pump Wells to meet system requirements.In this study,the data of heat pump system is monitored annually.In the cooling season of the combined heat pump system,the performance coefficient of the highest heat pump is COP=4.25.In the heating season of the combined heat pump system,the highest performance coefficient of the heat pump is COP=6.09.In the annual operation of the combined heat pump system,the heat pump system runs well,effectively realizes the utilization of clean energy,reduces carbon emissions,and realizes the annual production.Compared with residential buildings,agricultural buildings have the characteristics of obvious greenhouse effect,low thermal resistance of enclosure structure,and special physiological requirements of plants.According to the characteristics of facility agriculture,this study proposed a variable frequency control strategy of 40% fluctuation of circulating water pump on the basis of the original control strategy to solve the above problems existing in the application of the system in facility agriculture.TRNSYS software is used to carry out a series of dynamic simulation for the middle-deep geothermal combined shallow ground source heat pump.The simulation data is compared with the real data,and the results show that the difference between the simulated data and the actual data is 5.6%.Therefore,the model is deemed to meet the experimental requirements.According to the high energy consumption of heat pump system,different control strategies are evaluated based on the energy consumption of heat pump system.The circulating water pump system of the combined heat pump system is optimized.Based on the original control strategy,the circulating water pump is controlled by frequency conversion with fluctuation of 40%.By comparing the two different control strategies,it is found that the optimized control strategy can reduce the energy consumption of the heat pump system by 5.77%,which effectively realizes the purpose of energy saving.