Experimental and numerical investigation on energy-saving performance of radiative cooling coating for metal container office

Radiative cooling coating (RCC) embedded with randomly distributed particles is a scalable, cost-effective, and reliable material that can enhance the energy efficiency of the building envelope. Many RCC materials with excellent cooling potential have been developed recently. However, there is a lack of holistic experimental and numerical demonstrations of RCC’s energy-saving potential in real-world applications. In this research, by randomly distributing commonly used functional fillers into a polymeric matrix, an RCC material was developed and applied to an in-service metal container office at a construction site in Hong Kong. Parallel tests were conducted using another identical container office with conventional white coating for comparison. The inner and outer surface temperatures of the two container offices, their indoor air temperature, and the electricity consumption of their air-conditioner system were measured and compared. The field-test results indicated that the RCC could reduce the container office’s surface temperature by up to 18 ℃ and save 23.5% of electricity consumption under Hong Kong’s climate compared to the conventional white coating. Furthermore, the numerical simulation model for the metal container office was developed in EnergyPlus and validated by the experimental results. Then, the simulation model was used to evaluate the overall energy-saving performance of the RCC in five different climatic regions in China considering different solar reflectivity values. It was found that in tropical or subtropical cities such as Hong Kong, with the solar reflectivity of the RCC increasing from 85% to 95%, the annual energy load saving rate increases from 19.2% to 30.9%. In other climatic regions, the increase in the solar reflectivity will bring a significant increase in the heating load penalty that outweighs the cooling load savings. Therefore, in regions with hot summers and cold winters, optimizing the solar reflectivity of RCC by considering the offset between the cooling load saving and heating lead penalty is highly desirable in order to achieve the best annual energy-saving performance.