The islands in the South China Sea are characterized by year-round high temperatures and humidity, intense solar radiation, substantial building cooling loads, and a shortage of fossil fuel resources. There is an urgent need for low-carbon and energy-efficient solutions to meet local cooling demands. To address this, this study constructed a collaborative framework of "combining active-passive systems": leveraging natural deep-sea cold sources for cooling and rooftop photovoltaic power generation, while optimizing building layout and envelope to reduce cooling demand. Taking Yongshu Reef as a case study, numerical simulations evaluated the impacts of pipe diameter, flow velocity, and length on the heat transfer performance of a deep seawater closed cooling air conditioning system, determining the optimal combination of vertical pipes, horizontal pipes, and spiral coils. Concurrently, passive design was combined with optimized building layout and enclosure structure to reduce the cooling load of the building. Furthermore, proposed a circular layout strategy based on building energy intensity zoning to achieve efficient transportation of deep-sea cooling capacity through zoning. Simulation results show that using DN200 vertical and horizontal pipes, DN80 spiral coils, and maintaining a flow rate of 0.5 m/s, the heat transfer performance of the system is improved by about 10%. Passive design reduces building cooling energy consumption by 30.95%, combined with rooftop photovoltaic technology to supply energy to the system, ultimately achieving self-sufficiency in cooling for island buildings. This study provides a practical and feasible low-carbon path for the energy self-sufficiency of low-latitude islands.

Deep seawater closed cooling air conditioning system; Energy self-sufficiency; Low-carbon refrigeration; Optimization of building layout; Passive design; Photovoltaic power generation