Determination of the optimal thickness of vertical air channels in double-skin solar façades

Abstract

Using interior air layers in building envelopes has become popular in modern building design and construction. With the help of solar radiation, the air natural convection in these air layers provide multiple benefits to the building envelopes. The flow and heat transfer process of the solar driven natural convection in the air channels can greatly influence the performance of these envelopes. This study numerically investigates the flow and heat transfer process in the vertical air channels of double-skin solar façades, and evaluates the influence factors of the temperature and velocity fields, in order to determine the optimal channel thickness. The results show that the flow transition, velocity promotion and temperature increase mainly occur in the near-wall regions. For vertical channels with the height of 2-4m, the thickness of 0.1-0.8m and the input heat flux of 100-400W/m2, the flow rate varies between 0.042 kg/s and 0.255kg/s, and the range of the temperature rise is 0.66-14.70℃. Increases in the channel height and the input heat flux may result in a straight increase in the flowrate and the temperature, while the influence of the channel thickness on the flow rate and the temperature rise is limited. For air channels intending to improve ventilation capacity, the channel thickness should not be bigger than 0.6m; while for channels with the purpose of supplying warm air, the thickness should be less than 0.2m.