Flow and heat transfer characteristics of natural convection in vertical air channels of double-skin solar facades

Design and construction of internal ventilated air layers have become a popular way to improve the thermal performance of exterior envelopes in modern buildings. These air layers provide multiple benefits to the building envelopes, including improving the thermal insulation property, as well as achieving the effects of fresh air preheating, space heating, natural ventilation, passive cooling, etc. Obviously, the flow and heat transfer condition of the solar driven natural convection in these air layers can significantly influence the performances of these envelopes. This study numerically investigates the flow and heat transfer process, as well as the influence factors of the temperature and velocity fields, the induced air flowrate and the temperature increase in these air layer structures. The results demonstrate that the flow transition, velocity promotion and temperature increase mainly occur in the near-wall regions. For vertical air layers with the height of 2-4 m, the width of 0.1-0.8 m, and the input heat flux of 100-400 W/m(2), the air flowrate varies between 0.042 kg/s and 0.255 kg/s, and the range of the temperature rise is 0.66-14.70 degrees C. For air layers intending to improve ventilation capacity, the channel width should not be bigger than 0.6 m, while for those with the purpose of supplying warm air, the width should be lower than 0.2 m.