Structural optimization of novel three-source air conditioning integrating radiative sky cooling and evaporative cooling

The energy consumption reduction of air conditioning attracts much attention in hot summer and warm winter regions, since the high ambient temperatures seriously limit its refrigeration efficiency. Passive cooling technologies are promising in alleviating this problem, but require effective system integration and energy source coupling. In this paper, a novel three-source air conditioning (TSAC) integrating passive radiative sky cooling, evaporative cooling and air cooling is proposed. Its condenser tubes are directly integrated with the cooling plates, facilitating direct heat transfer from the cooling plates to the refrigerant during the condensation process. The condenser heat is utilized to increase the surface temperature of the cooling plates, thereby enhancing cooling capacity. A steady-state distributed parameter model was built and validated. An in-depth analysis of the heat exchange characteristics of the three-source condenser (TSC) is conducted from a 4E perspective, optimizing the tube layout and heat exchange structure to enhance the system's comprehensive performance. The results indicate that a plate thickness of 4 mm and a tube spacing of 48 cm yield optimal reductions of 19.56 % in electricity consumption and 12.15 % in life cycle costs compared to traditional air conditioning (TAC). Furthermore, the refrigerating characteristics of the hybrid air conditioning (HAC) are explored, which integrates the three-source condenser with air finned-tube condenser. A comparison is made between TAC, HAC, and TSAC in major cities across China. The results could guide the design and exploration of air conditioning integrating radiative sky cooling, evaporative cooling and air cooling as well as provide a valuable reference for the energy efficiency improvement of air conditioning.