To solve the low performance of Ground Coupled Heat Pump (GCHP) system in summer in cooling-load-dominated area, Borehole Cool Energy Storage (BCES), which uses soil for the storage and exchange of energy, was combined with hybrid GCHP systems (cooling tower as auxiliary equipment) to achieve efficient heating and cooling of buildings. Compared with GHE, BCES can provide more cool energy for buildings during periods of peak demand as a result of injection of cooling energy. Based on the coupled heat conduction and heat advection model for BCES, a diurnal cool-injection and extraction strategy for BCES in summer was adopted to determine the optimized thermal performance of the hybrid GCHP systems. With diurnal injection and extraction of cooling energy, the BCES system with 1 m pipe spacing supplied three times the cooling energy (88.9% from cool injection) of GHE without injection. After 90 days, the average increase in soil temperature was 0.96 degrees C for BCES compared with 4.29 degrees C for GHE. Furthermore, the effect of borehole depth and spacing showed that a hybrid BCES and GCHP system is useful in significantly decreasing the required borehole area, and in mitigating peak power load and improve ng operational efficiency. (C) 2015 Elsevier B.V. All rights reserved.