Radiative-cooling concrete as a low-cost heat-rejection solution for Geo-thermal energy storage in hybrid ground-coupled heat pumps

Cooling-dominated ground-coupled heat pumps (GCHPs) can suffer long-term ground heat build-up, increasing entering water temperature (EWT) and borefield length. This study evaluates a hybrid GCHP using a cement-based continuous cooling radiator (CCR) made from low-cost, durable passive daytime radiative-cooling concrete as a roof-area heat rejecter. A transient hourly model couples radiator heat balance, pump electricity, heat-pump coefficient of performance (COP) and ground heat-exchanger response over 10 years. Three climates were analyzed: Hong Kong, Phoenix and Singapore. Borefield sizing was constrained by EWT ≤ 40 °C and assessed through a 10-year life-cycle cost (LCC) framework. Compared with a standalone GCHP, the CCR reduces temperature-capped borefield length by 58–81% and gives the lowest 10-year LCC in all climates, with cost reductions of 23–42%. At 105 m 2 radiator area, the benefit is mainly capital-cost-driven and operational CO 2 reductions are modest because additional pumping can offset heat-pump electricity savings. At 240 m 2 near-roof coverage, the CCR provides clearer electricity and emissions reductions, up to ∼11%, while maintaining the LCC advantage. A screening comparison with conventional heating, ventilation and air-conditioning (HVAC) indicates a first-year cumulative cost crossover for the CCR-based hybrid system in all climates. These results suggest that radiative-cooling concrete can replace part of the drilled borefield with low-cost roof-area heat rejection, reducing a key deployment barrier for hybrid GCHPs in cooling-dominated cities.