Abstract:

The heat exchanger of medium-shallow borehole which have a deeper depth than the traditional ground source heat pump system and can sustain a notable load imbalance ratio and widen the application scope of geothermal energy. In order to investigate the long-term performance of medium-shallow borehole heat exchanger in the area with unbalanced cooling and heating load of buildings and the sustainable load imbalance ratio under different design parameters, a comprehensive numerical model is established based on the OpenGeoSys. The results show that the sustainable load imbalance ratio of medium-shallow borehole heat exchangers change with different scales. The load imbalance ratio of a single heat exchanger is 56 %, while the load imbalance ratio of the heat exchanger located at the edge of the array is the largest of 60 %, and the load imbalance ratio of the heat exchanger located in the center of the array is the smallest of 45 %. This indicates that the cold accumulation phenomenon will reduce the load imbalance ratio of the medium-shallow borehole heat exchanger. Therefore, in the actual operation process, the overall operation performance of the array can be avoided by shutting down some medium-shallow borehole heat exchanger located in the center of the array. Under three different arrangements, the load imbalance ratio of the medium-shallow borehole heat exchangers also changes, ranging from 53 % to 58 %. The average load imbalance ratio of the medium-shallow borehole heat exchangers in staggered arrangement is the highest, so it is recommended to adopt staggered arrangement in practical application. The results show that the newly proposed medium-shallow borehole heat exchanger can sustain a notable load imbalance ratio, and provide a basis for the design of medium-shallow borehole heat exchangers.

Key words: heat exchanger of medium-shallow borehole, pipe network characteristic, load imbalance ratio, long-term performance, design parameter, arrangement