Simulation of an energy-efficient cool roof with cellulose-based daytime radiative cooling material

Abstract

Conventional air conditioners are considered the most energy-intensive components in residential and tertiary buildings. Besides high energy consumption, they are also harmful to the environment due to the emissions of hydrofluorocarbons into the atmosphere. Night sky cooling or radiative cooling is a naturally occurring phenomenon that takes advantage of the atmospheric transparency window in the wavelength range of 8–13 µm to effectively dissipate heat from a surface into outer space. However, this can only occur at night, which is incompatible with the cooling demand that peaks during the day. This paper aims to develop a cool roof that relies on a daytime radiative cooling (DRC) material with low solar absorptivity in the wavelength range of 0.3–2.5 µm and high emissivity in the atmospheric window. The used DRC material is derived from cellulose acetate-based films, which are recyclable, sustainable, and bioclimatic. This material is used to improve the energy efficiency of an existing building by reducing the temperature of the roof to improve the thermal comfort of the building in the framework of Moroccan climatic zones. Software simulations are used to assess the needs and the demand of the building and simulate the impact of the smart device on the building's thermal performance and evaluate the thermophysical and optical properties of the DRC material. This latter material will be compared with another DRC material based on titanium dioxide and silicon dioxide mixture coating in terms of cooling performances. Results have shown a drastic sub ambient cooling of more than 3 °C and a great reduction in the indoor temperature of the building and a reduction in the total electricity consumption of up to 60.38 %.