The merit of applying variable-speed ground-source heat pumps (VSGSHPs) to displacement ventilation (DV) systems was investigated for use in offices in Hong Kong. To improve the dehumidification capacity of the DV systems, a sensible heat recovery wheel was added between the mixed and supply air streams with a heat recovery effectiveness of 0.4. By maintaining the peak fluid temperature leaving the ground heat exchanger borefield after one year to be the same, the required borehole depth and the total energy consumption of the modified DV system were reduced by 16.8% and 19.4%, respectively, as compared to a conventional mixing ventilation system which employed a constant-speed ground-source heat pump. This enhanced the economic feasibility of applying ground-source heat pumps to sub-tropical regions.

Practical application: The high initial cost of ground-source heat pump systems is the main obstacle to their wide acceptance in actual practice, particularly for application to sub-tropical regions where the air-conditioning demand is cooling-dominated. The present study demonstrates a design strategy in which both the initial and running cost of the ground-source heat pump systems can be reduced, thus enhancing the economic feasibility of the systems.