Parametric analysis and potential evaluation of an all-day radiative sky cooling radiator-assisted ground source heat pump system

Practical utilization of radiative sky cooling (RSC) in an active way to produce cold water breaks the cooling limitation of 150 W/m2 for passive RSC but requires thoughtful system design. Therefore, this study proposes a novel radiative sky cooling radiator (RSCR)-assisted ground source heat pump (RGSHP) system to maximize the cooling potential of using RSCR and GSHP. The RGSHP can take full advantage of the ground's thermostability to improve the cooling performance of the RSCR. Based on this developed hybrid system, the effects of designing parameters, weather conditions, and spectral properties of coatings on the performances of radiative cooling have been comprehensively investigated. The results show that a larger water flow rate is conducive to cooling power production of RSCR, but a smaller flow rate is beneficial to the COP improvement of the whole system. Moreover, compared with the ideal RSCR (iRSCR), the practical RSCR (pRSCR) shows comparable cooling performances due to the higher convective cooling performances, with an considerable annual average COP which is only 0.8 % smaller than the iRSCR-assisted GSHP system. Due to less heat rejected into the ground by RGSHP, the borehole wall temperature shows smaller values than stand-alone GSHP. For a ten-year simulation, the RGSHP system can reduce borehole wall temperature by 10.2 %. Moreover, using the RGSHP can also achieve cooling storage in the ground during the non-cooling seasons, and thus the RGSHP outperforms the GSHP by 13.2 % regarding the cooling season average COP.