Shape optimization of high-rise solar chimneys to improve the uniformity of flowrate distribution

Abstract

Solar chimneys (SC) are passive ventilation devices which can induce natural ventilation by utilizing solar radiation. Many studies of SCs have focused on single-storey or low-rise buildings, but much less attention has been given to SCs for high-rise buildings. This paper investigates the airflow induced by 10- to 50-storey SCs using an experimentally validated computational fluid dynamics (CFD) model. The effects of the total number of storeys and the air gap size on the induced average flowrate were first studied, and their correlations were derived through linear regression. The flowrate induced by a conventional SC with a constant air gap size is highly non-uniform. To improve the uniformity of flowrate distributions among storeys, a taper structure with a narrowing air gap downwards was proposed for multi-storey SCs. Numerical simulations show that adopting the taper structure can significantly improve the uniformity of flowrate distributions. For example, in a 20-storey SC, the flowrate difference between the maximum and minimum among the middle 17 storeys, normalised by the average, decreases from 122.8% to only 15.8% when the taper structure is adopted. A parametric study of 441 numerical simulation cases was conducted to derive the optimum ratios of the bottom gap size to the top gap size for taper multi-storey SCs. The results of this paper can provide guidance on how to design multi-storey SCs for high-rise buildings to exploit the potential of natural ventilation and reduce energy demand for cooling and ventilation.