| With the rapid development,popularization and application of ground source heat pump technology,many problems in the long-term continuous operation of ground source heat pump system have attracted extensive attention.The main problems in the operation of ground source heat pump system can be summarized as the change of underground rock and soil temperature caused by long-term continuous operation of the system,which will affect the continuous increase or decrease of outlet water temperature of buried tube heat exchanger,It will affect the heat exchange performance of the underground heat exchanger of the ground source heat pump system,resulting in low energy efficiency or even failure to work normally.In practice,the operation problems of the ground source heat pump system are not caused by a single factor or a single component in the system.The discussion on how to improve the operation and management of the ground source heat pump system needs to be considered from three aspects: the load characteristics of the user side,the unit and the underground heat exchange process.This paper takes the ground source heat pump system of a hospital as the research object.Firstly,the operation data of the system over the years are statistically analyzed to find out the problems in the actual operation of the system.Combined with the on-site investigation of operation and maintenance,the causes of the problems are analyzed and summarized,and then the idea of optimizing the operation and management of the ground source heat pump system based on the load characteristics of hospital buildings is established.Based on this idea,Firstly,the hourly load simulation model of the hospital is established.According to the hourly load simulation results,combined with the use characteristics of hospital buildings and zoning functional characteristics,the load characteristics of the main functional rooms of the hospital are analyzed.Then,the load bearing characteristics of the buried tube heat exchanger are analyzed and summarized according to the cumulative characteristics,load intensity variation characteristics and load persistence characteristics of the buried tube ground source heat pump system.The building load characteristics are reflected to the underground rock and soil through the heat pump unit.In the process of heat transfer,the compressor,evaporator and condenser are the main components.In this paper,the ten-coefficient simulation relationship of the refrigeration capacity and power consumption of the refrigeration compressor of the unit is established by using the ten-coefficient simulation method of the refrigeration compressor,and the correlation between the return water temperature of the buried tube and the heat absorption and discharge,power consumption and cop under the actual operating conditions is fitted.Because the demand of cooling and heating load on the building user side is certain,the analysis results of building load characteristics show that the daily load shows the time sequence law of uniform change at night and uneven change during the day with the service time and functional characteristics of hospital buildings.This paper uses this law to match the two with the load bearing characteristics of buried tube heat exchanger,and then formulates the zoning and time-sharing operation strategy of tube group;The tube group zoning model is established by using FLUENT software,and the UDF program is compiled to realize the phased operation of different zones.The operation simulation under continuous and intermittent operation modes is carried out with the hourly load of the building as the input condition.The hourly variation value of the return water temperature of the buried tube under different operation modes in each zone is used to calculate the heat absorption and discharge,cop and power consumption of the ground source heat pump host,so as to evaluate the effects of different zoning operation modes.The calculation results show that,compared with the continuous operation condition,the heat absorption and COP of the two main engines are improved under the operation condition of zoning and time division.The heat emission of the two main engines in summer is increased by 0.6% and 0.67%,and the heat absorption in winter is increased by 2.28% and 3.56%;COP increased by 3.2% and 2.5% in summer and1.7% and 2.3% in winter respectively;The power consumption is also reduced.The input power is reduced by 1.8% and 1.74% in summer and 2.34% and 2.39% in winter.Then,the total heat release and total heat absorption of the buried tube heat exchanger during the operation of the whole refrigeration season and heating season are calculated.The results show that the partition and time division operation only reduce the heat imbalance rate by1.1%,which can not effectively solve the problem of heat imbalance at the ground source side.The reason is that the heat imbalance at the ground source side is fundamentally determined by the cumulative cooling load and cumulative heat load of the building.If there is no additional cooling capacity or heat supplement,the operation of buried tubes in different areas and periods can not effectively solve the heat imbalance on the ground source side.Finally,based on the existing two forms of buried tube heat exchangers in the project,this paper puts forward a new "combined heat exchange model of buried main and auxiliary tubes",and simulates its working effect by using FLUENT software.The simulation results show that under the set operating conditions,the double U-shaped and pile foundation three spiral main and auxiliary tubes operate together,and the downstream and countercurrent of the auxiliary tubes can effectively use the natural cooling capacity and building waste heat to strengthen the heat exchange of the main tube,Furthermore,the inlet and outlet water temperature difference of the main buried tube in winter and summer is increased by 2.33 ℃in summer and 2.19 ℃ in winter.However,due to the composition principle of the model,the combined heat exchange of the main and auxiliary tubes of the double U-shaped buried tube can not effectively ensure the heat exchange demand of the single hole design;The combined heat exchange model of the main and auxiliary tubes of the pile foundation three spiral buried tube heat exchanger can also effectively use the natural cold source and construction waste heat,so as to improve the inlet and outlet temperature difference of the main tube.The simulation results show that the heat exchange temperature difference of the main tube can be increased by 1.15 ℃ in summer and 1.15 ℃ in winter.The total heat exchange check results show that it can greatly improve the total heat exchange of a single pile under the condition of overcoming the defects of the model.Finally,the utilization ratio of natural cold source and building waste heat of the heat transfer model is calculated according to the simulation results of the combined operation of the three spiral main and auxiliary tubes of pile foundation in winter and summer.Through the simulation and calculation results of continuous and intermittent operation of two different forms of buried tube heat exchangers and the separate and joint operation of main and auxiliary tubes,it can be seen that the heat exchange performance and operation stability of double U-shaped buried tube are better than pile foundation three spiral buried tube,but pile foundation three spiral buried tube is easier to strengthen its own heat exchange by using certain measures to achieve good operation effect.In the actual project application,in order to ensure the load demand and heat exchange effect at the ground source side,double U-shaped buried tubes should be used as the main,supplemented by pile foundation spiral buried tubes,which complement each other and operate alternately.Certain measures should be taken to strengthen the heat exchange of pile foundation spiral buried tubes and form a ground source heat pump system in the form of multi buried tube heat exchange. |
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