Optimization And Analysis Of Heat Transfer Performance Of Ground Source Heat Pump In Suzhou Area

The scarcity of resources and environmental pollution caused by energy consumption have become a global problem.It is urgent to find and use sustainable clean energy.Geothermal energy,with its wide distribution range,stable temperature,clean environmental protection and other characteristics,gradually attracted attention.Ground source heat pump technology is to use the characteristics of geothermal energy to achieve summer to underground heat,winter from underground heat,so as to achieve the purpose of indoor refrigeration and heating to the building.This paper takes a building in Yongqiao District,Suzhou City as the prototype,combined with the actual engineering parameters and operating conditions,using COMSOL software to establish a three-dimensional coupling heat exchange model of vertical single U buried pipe and soil,and carry out the geotechnical thermal response test of this project to obtain the relevant parameters.Then,the actual operating conditions of the project were taken as the initial conditions to simulate and analyze the heat transfer process of the model under the same parameter conditions.The results of the simulated numerical calculation were compared with the data collected under the actual operating conditions.The results showed that: The trend of the simulated outlet water temperature is consistent with that of the data collected under actual operating conditions.The maximum difference between the two is only 0.6℃,which is less than 5% of the actual value,thus verifying the accuracy of the model and the rationality of the numerical simulation and calculation method used in this paper.By simulating the heat transfer process of buried pipe heat exchanger and controlling the single variable,the influences of different inlet temperature,inlet flow rate,thermal conductivity coefficient of return filler,buried pipe depth,soil initial temperature,soil thermal conductivity coefficient,and thermal conductivity coefficient of buried pipe on the heat transfer performance of buried pipe heat exchanger are obtained respectively.The results show that the increase of inlet temperature can increase the heat transfer of the system.When the temperature reaches 37℃,the heat transfer per unit well depth is basically constant,but the efficiency of the heat pump is very low.The optimal inlet temperature range is recommended between 26℃ and 30℃.The increase of inlet flow rate within a certain range can improve the heat transfer performance of the system.The flow rate reaches 2.3m/s and is basically stable,but the energy consumption of the pump increases.The optimal influent velocity is recommended to be between 0.8m/s and 1.2m/s.With the increase of thermal conductivity of backfill,the heat transfer performance can be improved,but when the thermal conductivity exceeds that of external soil,the trend gradually flattens out.Therefore,the thermal conductivity of the backfill should not be too large.It is better to have a similar or slightly higher thermal conductivity with the external soil.In general engineering,the original soil is used for backfilling.The deeper the buried pipe depth is,the heat transfer per well increases gradually,but the heat transfer per well depth decreases gradually,and the investment cost increases.Therefore,drilling depth should not be increased blindly.The most reasonable drilling depth should be determined according to the comprehensive consideration of building load and drilling utilization rate.The lower the external soil temperature in summer,the better the heat transfer performance,and the higher the external soil temperature in winter,the better the heat transfer performance.Therefore,it should be determined by combining the operating time and load analysis of local winter and summer working conditions.The greater the thermal conductivity of the soil,the better the heat transfer performance,and the performance change has a great relationship with the thermal conductivity of the back filler,so when the buried pipe is buried,the area with the large thermal conductivity of the soil should be selected as far as possible,and the thermal conductivity of the back filler should be kept close to the soil thermal conductivity.In general engineering,the original soil is used to backfill;The higher the thermal conductivity of the buried pipe,the better the heat transfer performance,but the improvement effect is gradually getting worse,so when choosing the buried pipe material,there is no need to blindly pursue the material with large thermal conductivity.In engineering,the general selection of the thermal conductivity of 0.4W /(m·K)～ 0.45 W /(m·K)of the buried pipe can meet the needs.Finally,combining with the buried depth of the pipe and the soil initial temperature on the results of the analysis of the influence of the buried tube heat transfer performance,this paper proposes a well with cold and hot condition in thermal conversion system,made in the same drilling,through to the buried pipe add valve device,implement the system under the condition of winter and summer respectively with different depth and temperature of the soil for the purpose of the heat transfer,Thus,the heat transfer efficiency of the system can be improved in summer and even in the whole year.The results show that under stable working conditions in summer,the heat transfer per unit well depth of shallow layer is increased from40.76 W to 62.45 W,the heat transfer efficiency is improved by 53.2%,and the heat transfer performance is significantly optimized.Based on the analysis of the influencing factors of the heat transfer performance of buried pipes in suzhou area,this paper proposes the heat transfer device under cold and hot conditions of the same well,which has certain reference value and reference significance for the design of buried pipe heat exchanger of ground source heat pump in suzhou area or the area with similar hydrogeological environment.