Analysis Of Ground Source Heat Pump System Based On Soil Thermal Balance

As the importance of building and air conditioning energy conservation being more realized, the ground source heat pump technology which utilizes renewable energy has been rapidly developed in recent years. Many demonstration projects of ground source heat pump have been built throughout the country. However, the technology is far from mature owning to the short period of development. Practical operation effect of the system is not that good in quite lots of projects. The ground heat imbalance is one of the most common problems. The inequality of the building cooling load and heating load results in the imbalance of the cumulative heat extraction and rejection of ground heat exchanger. After a long period of running, the ground temperature would drop or rise year by year and could never recover again. And the system efficiency may decline a lot by then. Thus, the study of thermal equilibrium problems should be taken seriously enough.Based on the project of a very large office building, Nanjing XinCheng mansion, this paper introduced the application of the vertical borehole ground-source heat pump. Taking the ground heat balance as the main consideration, the paper analyzed the main factors which affect the heat balance during the process of design. And some optimization design methods have been proposed to resolve the thermal equilibrium problem. I expect to provide some reference opinions over the design of the ground source heat pump projects which are similar with XinCheng mansion.In this paper, the annual dynamic loads of the building are calculated through the simulation of DeST. And I also analyzed the characteristic of the data. The building is located in Nanjing, a zone with hot-summer and cold-winter. The ratio of annual cumulative cooling load to heating load is up to about 2.78:1. The cooling loads and heating loads are quite disequilibrium. This architectural is an office building, so the air conditioning system works for 12 hours per day. The long period of intermittent would be advantageous to the temperature recovery of the ground. About the design of cooling and heating source scheme, the technique of heat recovery as well as an auxiliary cooling tower is adopted in this project to adjust the load peak.Through the study of the geotechnical characteristics, the feasibility of the ground source heat pump system applied in XinCheng mansion are analyzed in this paper. The ground heat exchangers were designed based on the results of the geotechnical thermal response test. The paper also discussed about how did the bury space, depth and bury way of the underground heat exchangers influence the ground heat balance. The conclusion is as follow: when we determine structure parameters of the underground heat exchangers, the characteristics of the project should be considered, too. Analysis of one single factor doesn’t make any sense.