Energy assessment of a roof-integrated phase change materials, long-term numerical analysis with experimental validation

Abstract

• Thermal behavior of roof-integrated PCM is evaluated. • Two modeling methods of PCM are conducted, compared and validated. • Long-term simulation is condcuetd to evaluet the perfromnec of roof-integrated PCM. • The average inner wall temperature was 32.4 ˚C and 29.4 ˚C for the roof without and with PCM respectively. • A 40% decrease in the summer total energy gain is attained due to the use of RT31-PCM in the roof. Achieving the concept of energy efficient building (EEB) is a promising direction for global energy saving. The incorporation of phase change materials (PCM) in the building structure is one of the new techniques recently applied in EEB. However, many recent investigations used short-term analysis of roof integrated PCM. Therefore, long-term thermal behavior of building roof containing PCM layer is investigated in this study. The roof with and without PCM layer are compared at variable outside weather conditions. Enthalpy-porosity model along with a simplified thermal model are developed and simulated using ANSYS-Fluent. The enthalpy-porosity model is essential to capture the melting behavior inside the PCM layer, while the simplified model is the appropriate model for long-term simulation. The two models are compared and validated with the experiments conducted in this study and with data in the literature. Roof with three different PCMs and three thicknesses are evaluated. Long term simulation is conducted for both roof with and without PCM in hot summer season of Aswan city, Egypt. The results showed that using PCM in the roof structure decreases the indoor heat flux and attains an indoor wall temperature closer to the indoor air temperature requirements. Further, the larger thickness of the PCM, the better performance. Based on four months’ simulation, the average predicted indoor wall temperature reached 32.5 ˚C and 29.4 ˚C for the roof without and with PCM respectively. Furthermore, around 40% decrease in the total energy gain in four summer months is attained due to the use of 40 mm of RT31-PCM in the roof structure.