Photothermal and energy performance of an innovative roof based on silica aerogel-PCM glazing systems

Abstract

The glazing systems are considered as the critical components in terms of the building energy consumption owing to the undesired insulation performance and poor thermal inertial mass. To overcome those challenges, the glazing systems integrated with silica aerogel and PCM (SA-PCM) are confirmed as a promising technology to improve photothermal performance. However, the inevitable conflict remains between the energy saving and daylighting performance when the PCM and silica aerogel are filled into two different layers. Therefore, an innovative roof based on SA-PCM glazing systems is proposed, in which the original PCM layer is divided into five cavities for filling PCM and air. A numerical model to investigate the thermal performance and energy efficiency of the innovative roof is developed. The evaluation of the thermal performance of the innovative roof is conducted by the indicators of temperature decrement factor and temperature time lag, while the energy efficiency is evaluated by the total heat loss through the inner surface of the innovative roof. To evaluate the optical performance of the innovative roof, the dynamic optical properties (transmittance, absorptance, and reflectance) are obtained in conditions of different PCM fill ratios. The photothermal and energy performance of the innovative roof are investigated over a 24-hour period in the severe cold region of the city Daqing (China). The results show that the thermal performance of the innovative roof is improved with the addition of PCM amount embodied in the decrease in magnitude and the increase in phase shift of temperature waves on the inner surface. Besides, both the transmittance and absorptance of the innovative roof change significantly along with the PCM fill ratio over the course of the day, while the change in reflectance is slight. Additionally, the optimal energy performance of the innovative roof occurs at 80% fill ratio of PCM, in which the total heat loss and the energy saving rate account for 2595 kJ/m2·d-1 and 11.37%, respectively. Based on the principle of prioritizing the energy efficiency while considering the demand for light transmission properties of the innovative roof, the fill ratio of PCM is recommended as 60%.