New Concept of a Ground-Source Refrigeration and Air Conditioning System with Cross-Seasonal Energy Storage Capability

Abstract

The performance of a conventional Ground-Source Refrigeration and Air Conditioning (GSRAC) system with a borehole heat exchanger (BHE) can be enhanced by addressing the soil thermal imbalance issue that affects these systems. This study proposes a novel concept for seasonal cold energy storage using a Thermal Diode Tank (TDT). The TDT consists of an insulated water tank fitted with an array of heat pipes. By integrating the TDT into a conventional GSRAC system, “cold” energy can be passively collected from ambient air during winter, injected into the BHE, and stored in the soil. The stored “cold” energy can then be retrieved in the summer, facilitating cross-seasonal cold energy storage (CS). Thus, a conventional GSRAC system can be transformed into a GSRAC system with cross-seasonal cold energy storage capability, i.e., GSRAC + CS system. The validated BHE model previously developed by the authors is used to predict the performance improvements achieved using the GSRAC + CS system. The results indicate that the Annual Net Cold Energy Storage Efficiency (ANESE) increased from 5.7% to 10.7% over a ten year period. The average Borehole Performance Improvement (BPI) due to the addition of cold storage capability is 11% over the same timeframe. This study also discusses the impacts of varying design and operational parameters on ANESE and BPI. The results demonstrate that GSRAC + CS systems not only mitigate the soil thermal imbalance issue faced by conventional GSRAC systems, but also require less BHE depth to achieve equivalent performance.

Keywords

• borehole thermal energy storage
• cross-seasonal energy storage
• seasonal cold storage
• heat pipe