Effects Of Water Source Heat Pump On Temperature Fields Of Aquifers And Suitable Zoning

With the rapid economic and social development of the Beijing-Tianjin-Hebei region,the energy problem is becoming one of urgent issues that need to be solve.Currently,the issues are low heat exchange efficiency,high pump consumption and heat connection of underground heat exchanger due to groundwater level keep decreasing;and in the actual application,using practical experience is how thermal connection often be judged,lack of advanced theoretical guidance.In addition,to be sustainable and efficient of geothermal resources involves sedimentary environment,thermal properties,hydrogeological parameters,geochemistry,geothermal energy and other disciplines.This study is based on the Coordinated development of Beijing-Tianjin-Hebei with Huanghua,Haixing 1:50 000 environmental geological survey and had field pumping test,water analysis and numerical simulation analysis in Huanghua firstⅣwater group of groundwater system,got regional groundwater flow field,temperature field,groundwater geochemical characteristics.This study also discussed the influence of underground water source heat pump cold fluid recharging on hydrogeology,preliminarily divided suitable area for underground water source heat pump system,which can provides reference for related theoretical researchs and practical applications.Research results as follow:1)First of all,the study area of groundwater hydrogeological investigation firstⅣwater group.The distribution characteristics and hydrogeological parameters of rock strata in key areas were obtained by drilling coring and field pumping experiments.HHSW04-01 borehole aquifer thickness and average permeability coefficient were57.6m,39.6m,80.1m,37.5m and 2.2m/d,2.7m/d,3.3m/d and 2.0m/d,respectively.With the increase of drop depth,the radius of influence increases gradually and the unit water inflow decreases gradually.The unit water inflow is between 1.6 and 3.9L/（s·m）,which belongs to strong water-rich.The p H value of groundwater is 7.9-8.3,and the hydrochemical type is mainly CI-Na,followed by HCO₃-NA and SO₄-Na.2)Use cationic thermometer to predict the reservoir temperature in the target area of the water source heat pump system.The results showed that the geothermal gradient in the study area was 2.9-4.3℃/100m.The temperature that the thermal reservoir can reach or that the geothermal water once reached is 51-60℃,and the circulation depth of the geothermal fluid is about 1105-1315m,which belongs to the warm water in the low-temperature geothermal resources.3)Based on the finite element simulation software FEFLOW,modeling the three dimensional numerical model of firstⅣstudy area groundwater aquifer group,the groundwater trend from June 2010 to December 2010 was used to validate the model.Based on the analysis of the influence of groundwater extraction volume in December2017 on groundwater level in the research,and predicted groundwater flow field in the next five years to provide a reference for the appropriate regional division of water source heat pump system.The results show that the smaller the flow rate,the smaller the drop depth,and the more stable it tends to be.At the same pumping flow rate,the intermittent extraction with small flow rate and small drop depth has little influence on the water level of the aquifer.Groundwater recharge in the study area mainly comes from the northwest and the south;Due to the influence of groundwater exploitation in the eastern industrial zone of Cangzhou,it is difficult to recharge the groundwater level in southwest China.In northwest China,the Yellow River is used,by stopping the exploitation of underground water and the recovery of underground water level is relatively obvious.In the east,groundwater is less exploited,and the groundwater level changes little,the groundwater below the sea level is basically stagnant.The groundwater level decline is mainly concentrated around the urban area and near the industrial area,with a depth of 5-10m.It belongs to mining and desiccation type.4)By analyzing the influence of the thermal transfixion process in key areas on the temperature field of the aquifer,with the groundwater flow field,temperature field change,chemical field,and groundwater level change trend in the next five years,we preliminarily divided the suitable areas of the water source heat pump system.The results show that the drilling HHSW01 southern coastal region of groundwater in the study area have relatively high temperature,shallow water depth,large permeability coefficient,rich in water,the outlet water temperature is relatively high and effect of recharging on temperature field is relatively small,belongs to the upstream in the study area,It is a suitable area to realize economical,efficient and stable operation of water source heat pump unit.