Influence of permeability ratio on wind-driven ventilation and cooling load of mid-rise buildings

Abstract

Natural ventilation potential in terraced buildings is affected by numerous parameters such as permeability ratio, distribution pattern, depth of terraces, etc. This research aims to evaluate the impact of permeability ratio on natural ventilation potential and cooling load of a terraced office building in the hot- humid climate. To this end, one solid block and eight porous models with different permeability ratios (20 %–30 %–40 %–50 %) and random distribution patterns were simulated and analyzed by Energyplus engine and computational fluid dynamics (CFD). For better comparison, two distribution patterns for each permeability ratio were simulated. CFD simulations were validated according to the wind-tunnel measurements. The cooling load amount, mean and maximum airspeed as well as the mean age of air in terraces and offices were used to evaluate the best configurations of porous buildings.The results show that increasing the permeability up to 50 % will enhance the interior and inlet airspeed by 38.59 % and 49.07 % compared to the solid case. Simulations proved that a small change in porosities from 20 % to 30 % resulted in a significant difference in mean and maximum airspeed in terraces. The case with 50 % permeability ratio indicated higher values of mean and maximum airspeed in terraces. The mean age of air amount follows a descending process from the permeability ratio of 0–30 % and then increases gradually. The 30 % porous model with 30.8 s mean age of air is considered as the best case.According to the results, the introduction of permeability does not leave a positive effect on cooling energy demand despite natural ventilation performance. Although porosity reduces the solar radiation heat gain and increases the natural ventilation potential, porous models indicated high values of cooling energy consumption. This is due to the high amount of exposed surface area in porous models which leads to an increase of cooling energy demand up to 2.7 % compared to the solid case.As a result, among the permeable models, the best natural ventilation performance and the lowest cooling energy consumption are attributed to 50 % and 20 % permeable groups respectively.This study helps the designers to better understand the ventilation and energy performance of a porous model and to improve the energy-efficient buildings in hot-humid regions.