地下水源热泵运行模式对地温场效能影响研究

基于上海市某地下水源热泵工程项目,采用COMSOL Multiphysics有限元分析工具建立二维简化的热渗耦合数值模型,模拟采能区含水层多孔介质热量运移过程,并利用热泵运行3年的现场监测数据进行模型的识别与验证。探讨热泵系统冷、热负荷设计和抽、灌模式两个方面对采能区地温场效能的影响,分析和预测不同工况下热泵运行期间地温场的演变特征,最后对系统的运行效果进行评价。结果表明:该热泵系统按原设计方案运行时,抽灌井短期运行效果良好,但在第7个供暖期末将出现热贯通现象,长期运行将不利于热井的取热; 如果减小20%热负荷、增加20%冷负荷,会使冷影响区扩散速度降低46.3%,系统运行效果得到显著改善,在模拟的9个运行周期内并未出现热贯通现象,说明合理调节冷、热负荷有利于热泵系统的长期稳定运行; 当冷、热负荷恒定时,分别减小10%和20%的循环水量将会使冷影响区扩散速度分别降低9.3%和15.7%,有效地缓解了热贯通的发生,且仍能满足项目对于制冷供暖的需求,进一步阐明了地下水源热泵系统宜采用“大温差、小流量”的抽灌模式。

Research on Influence of Operation Mode on Geothermal Field Efficiency of Groundwater Heat Pump

Based on a groundwater heat pump project in Shanghai, a 2D simplified coupled thermal conduction and groundwater seepage numerical model was established to simulate the heat transport process of porous media in the production aquifer by means of finite element analysis tool COMSOL Multiphysics, and the field monitoring data of heat pump operation for 3 years were used to identify and verify the model. The efficiency influenced by cooling/heating load design and pumping/injection mode of heat pump system were discussed on geothermal field under different working conditions in production area, the evolution characteristics of geothermal field during operation of heat pump were predicted and analyzed, and finally the operating effect of the system was evaluated. The results show that when the heat pump system is running according to the original design scheme, the pumping and injection wells have a good short-term operation effect, but the heat transfixion phenomenon will occur at the end of the 7th heating period, which means that long-term operation will not be conducive to the heat production of hot wells. If 20% heating load is reduced and 20% cooling load is increased, the diffusion velocity of cold affected zone is reduced 46.3%, the operation effect of the system is significantly improved, and heat transfixion phenomenon will not occur within nine simulated operating cycles, which indicates that reasonable adjustment of the cooling and heating load is beneficial to long-term stable operation of heat pump system. When the cooling load and heating load is constant, the diffusion velocity of cold affected zone decreases by 9.3% and 15.7% respectively when the circulating water flow decreases by 10% and 20% respectively, the heat transfixion phenomenon is effectively alleviated, and it can still meet the needs of the project for refrigeration and heating. It is further clarified that the pumping and irrigation mode of large temperature difference and small flow should be adopted in the groundwater source heat pump system.