Exploring the cooling potential maps of a radiative sky cooling radiator-assisted ground source heat pump system in China

Practical implementation of radiative sky cooling (RSC) in an active manner requires thoughtful system design. This study proposes a hybrid system that combines ground source heat pump (GSHP) and all-day RSC radiators (RSCR) to improve the systematical energy efficiency and assesses the cooling potential of RSCR as a supplemental part in GSHP across China using regional meteorological data. The study systematically evaluates the advantages in the energy efficiency of the hybrid system, the temporal cooling potential variability of RSCR in seven geographic regions of China, and the effects of varied radiative coatings with different spectral properties on the cooling capacity. The results indicate that the annual average cooling power provided by RSCR ranges between 149.7 and 484.6 W/m2 across all regions of China, with the highest cooling potential of 336.5 W/m2 observed in the cold region of north China and the lowest cooling potential of 178.3 W/m2 in the tropical region of south China. Compared with the stand-alone GSHP system, the heat rejected into the ground can be reduced by 20.6% on the nationwide average, and the nationwide average coefficient of performance (COP) of the proposed system can be increased by 18.6% due to the additional cooling contributions from RSCRs. All seven regions show promising cooling capacities for using RSCR as a supplemental heat rejector in winter compared to summer, with the maximum cooling power production of 453.6 W/m2 observed in winter in northeast China, corresponding to a temperature drop in RSCRs of 4.1 degrees C. The comparison between the diurnal and nocturnal cooling power productions across China reveals that the nocturnal cooling potential is higher than the diurnal scenario, with an average deviation of -66.2%, ranging from -53.7% to -78.8%. Moreover, compared to the ideal RSCR, the practical RSCR has a smaller radiative cooling power production (-18.2%) but a larger convective cooling power production (+1.6%), resulting from the relatively higher surface temperature on the practical RSCR, and the ideal RSCR-assisted GSHP system is 5.0% higher than that of the practical RSCR-assisted GSHP system regarding the nationwide average COP. The findings of this study can provide valuable insights into the better utilization of this energy-saving technology across a variety of weather conditions in China.