Influence of terrain and atmospheric boundary layer on the ventilation and thermal comfort performance of windcatchers

Abstract

Windcatchers are a promising natural ventilation alternative to conventional ventilation systems. In recent years, many studies attempted to address the different gaps in the field but the impact of terrain type on the performance of windcatchers is still an unexplored topic. Therefore, this paper investigates how the windcatcher's ventilation performance and thermal comfort are affected by different types of terrain and atmospheric boundary layer (ABL) profiles. To reach this goal, numerical simulations were employed and validated against experimental data. The performance was assessed in four terrain types (open, rough, suburban and urban) and two thermal scenarios (outdoor temperatures of 21.5 °C as the Nottingham's average maximum daily temperature for July and 26 °C as the summer design temperature). As the terrain changes from a more uniform open countryside to a less uniform urban region, the induced flow rate decreases from 1040 L/s to 690 L/s, which still surpasses the values of 160 L/s and 94 L/s recommended by the CIBSE and ASHRAE 62.1 standards. The maximum mean age of air (MAA) at the breathing height of a seated person reaches the value of 173 s and 190 s for suburban and urban regions while it does not exceed 140 s for open and rough country. Thermal comfort was assessed based on PMV and the adaptive model. The results showed that in the 1st thermal scenario (at an outdoor temperature of 21.5 °C), all terrains are within the adaptive comfort band. However, PMV was out of the comfort range in nearly 50% of the seated head height plane. However, in 2nd scenario (outdoor temperature of 26 °C), all terrains failed to provide comfort. Furthermore, the urban cases showed higher temperatures and PMV in both scenarios.