Numerical study on heat transfer characteristics of spray cooling double skin façade

Abstract

Using spray cooling technology to solve the overheating issue in double skin façade (DSF) is an important attempt to reduce building energy consumption. While, the thermal performance of the spray cooling double skin façade (SC-DSF) is not very clear, especially the complicated heat transfer characteristics. In this study, a comprehensive numerical model of SC-DSF system including solar radiation and two-phase flow problem is established by using three-dimensional steady Euler-Lagrange method to analyze the heat transfer characteristics from a microscopic perspective. And the CFD model is validated by the experiment. Meanwhile, a quantitative analysis is conducted to investigate the thermodynamic and kinetic behavior of the SC-DSF in hot humid climate region in China. The influences of outdoor air relative humidity, solar radiation intensity, and outdoor wind speed on the water spray cooling effect of the DSF are analyzed. The cooling efficiency of SC-DSF system is sensitive to the outdoor relative humidity. In a sufficiently cooled condition, the minimum temperature in the cavity is close to the outdoor wet-bulb temperature. The spray cooling efficiency reaches 28.2 % with the outdoor relative humidity of 20 %, but decreases to only 9.3 % as relative humidity rises to 80 %. Outdoor wind speed also has some impact on the spray cooling system, an optimal outdoor wind speed of 1.5 m/s can enhance cooling efficiency by 6.6 %, but it has adverse effect on the cooling efficiency when wind speed exceeds 3 m/s. However, in addition to increasing surface temperature of the DSF, solar radiation has little influence on the cooling performance. Excessive humidity exceeding 80 % and wind speed surpassing 3 m/s may render the spray system ineffective. Therefore, the effects of environmental conditions should be fully considered and utilized in the design and application of spray cooling systems.