Experiment and modeling on the heat transfer of U-vertical ground coupled heat exchanger

Category Other
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Lei, Haiyan; Zhu, Neng
Holding Date 07 October 2008

The temperature at a certain depth underground keeps nearly constant all-year, in order to exploit the heat of the ground, it is an effective way to use an array of buried pipes along the length of a building or buried vertically into the ground as a heat-exchanger system, and water is used for circulating medium to extract heat from the building and dump it to the ground in summer and vice versa in winter.
Studies show that borehole heat exchanger (BHE) has better performance and energy efficiency than horizontal ground heat exchanger. Correct sizing of the BHE continues to be a cause for continued design concern, and special attention should be placed on minimizing interference between neighboring BHE. Key points are building load, borehole spacing, and borehole fill material and local soil characterization.
This paper describes U-vertical ground coupled heat exchanger (UGCHE) experimental system, The main objective of the study is to investigate the performance characteristics of a Ground source heat pump system (GSHPs) with 120 m vertical deep 250 mm diameter of UGCHE both in summer and winter. Inner heat source model is used for simulating heat transfer process of UGCHE and temperature change of ground near to BHE, influence of different soil characteristic and fill materials on heat transfer and ground temperature are analyzed, results show that ground temperature can be used as heat sink for GSHPs effectively, and GSHPs is more appropriate to be used alternatively in summer and winter, which can be a theoretical basis for GSHP system design.
In addition, it is known that cooling load is much higher than heat load in China. Long time operating of GSHPs may results in imbalance of ground temperature. To maintain the heat source of GSHPs stable, mixed system, BHE plus cooling tower in summer or BHE plus additional heat source in winter, should be used to balance ground temperature.