Analysis of the thermal and energy saving performance of the concrete roof with radiative cooling coating

Abstract

It is recognized that a substantial portion of the cooling load in buildings originates from the rooftop, which presents a direct and opportune avenue for the implementation of radiative cooling technologies for building energy conservation and thermal comfort enhancement. In this study, a long-term field test was performed on an in-service office building with the heavy-construction roof in Hong Kong, which revealed that the radiative cooling coating (RCC) on the concrete roof could effectively reduce the rooftop outside surface temperature by 21.1 °C at the maximum. As a result, the RCC can turn the disadvantage of the high thermal mass of concrete roofs (absorbing heat during daytime and continuously releasing heat at night) into an advantage of storing coolness at night while continuously cooling down during the day, achieving a 1.5 °C lower temperature on the inside surface of the roof compared to the indoor air temperature throughout the day. When the air conditioning (A/C) system was operated with identical settings, the concrete roof with RCC consistently reduced the indoor air temperature by 2.8 °C, concurrently achieving a 20 % reduction in electricity consumption (i.e. 8 kWh per day during 8:00–18:00) as compared with the reference case. Heat-transfer building modeling analyses further demonstrated that under extreme external weather conditions and with a cooling setpoint maintained at 26 °C, the RCC significantly improved indoor thermal comfort. Additionally, it achieved an average annual cooling energy savings of 49.42 % (equivalent to 1108.74 kWh) across various cities in China.