Parametric study on a wall-mounted attached ventilation system for night cooling with different supply air conditions

Abstract

Night ventilation is a sustainable approach to achieve comfortable built environment with relatively low energy consumption in summer. However, the cooling performance of conventional night ventilation in the hot summer climate zone is unsatisfactory due to the insignificant climatic potential. Considering that a large proportion of the heat gains is stored in the building envelope, particularly in the external wall, we propose a novel wall-mounted attached night ventilation (WANV) for night cooling. This novel system is capable of generating a downward air jet that directly flows over the internal surface of the west-external wall to achieve enhanced convective cooling performance on the west wall during the nighttime. The present paper numerically investigates the air flow patterns and temperature field distributions in the test chamber with WANV under different supply air conditions (air velocity and temperature). The shear-stress transport k–omega turbulence model, a blending two-equation eddy-viscosity turbulence model which is suitable to capture airflows with strong streamline curvature and separation, is employed in the numerical study. Comparisons between the experimental data and the simulation results are carried out, and the good agreement suggests that the numerical model is able to predict the air velocity and temperature profiles of the chamber with WANV. The simulation results show that intensive air recirculation and enhanced convection are achieved due to the high turbulent air momentum in the scenario with WANV. A similar tendency of the decay of air velocities in the near-wall region is observed regardless of the supply air velocity. Furthermore, a correlation between the air velocity and the height above the floor is proposed. The cooling performance of WANV is significantly improved by decreasing the supply air temperature. Additionally, the impact of supply air conditions on the cooling performance is quantified using the relative heat releasing effectiveness index, which suggests that the optimal supply air velocity is approximately 4 m/s in hot summer at Chongqing or locations with similar climate conditions.