Impacts of key parameters on air natural convection characteristics in vertically parallel double-structural facades comprising phase change materials for passive heating

Vertical facades with phase change materials (PCMs) have attracted much attention owing to their energy saving. Natural convection within the channels undoubtedly plays a crucial role in their performance. However, current research primarily focuses on energy efficiency and macro-level configurations. Therefore, the research focuses on the characteristics of natural convection of air in vertically parallel double-structural facades, with one facade being PCM and the other facade being glazing. The effects of key influence parameters on its temperature and airflow characteristics are examined using computational fluid dynamics (CFD). The influencing parameters include the channel height and width, solar radiation flux incident on the glazing, and PCM melting temperature, respectively. Moreover, the induced mass flow rate and temperature rise of the channel are studied. Results showed that the temperature and turbulent kinetic energy in the near-facade area are higher than in the center area. However, the velocity in the near-facade area is lower than in the center area. For studied channels, the induced mass airflow rate in the across-section near the exit varies from approximately 0.0016 kg/s to 0.014 kg/s, and the induced air temperature increase fluctuates between 2.8 °C and 20.0 °C. Moreover, the results show that the aspect ratio should exceed 20, and the preferred PCM melting point should be 6 °C higher than the inlet air temperature. The findings could offer valuable theoretical guidance for designing and constructing the vertically parallel double-structural facades incorporating PCMs for high-performance heating.