Re-evaluating Local Ventilation Effectiveness Guidance for Single-Zone Naturally Ventilated Spaces

Ventilation effectiveness describes how effective a ventilation system is at getting “fresh” outdoor air into a space and is strongly associated with indoor air quality and energy efficiency. Whilst natural ventilation is ubiquitous worldwide, its effectiveness is poorly understood. Despite a lack of empirical evidence, current design guidelines claim that natural ventilation systems are only suitable for narrow floor spaces, due to the limited depth which fresh air can penetrate in deeper plan buildings. This study investigates this claim by quantifying the ventilation effectiveness of single-zone spaces employing top-hung and side-hung windows through full-scale physical experiments and validated computational fluid dynamics simulations.

The experimental results show that, regardless of the ventilation configuration, for prevailing outdoor wind speeds ranging from 4 to 85 km/h (1.1–23.6 m/s), all the tested scenarios, with window-to-wall ratios varying from 3.5–9.7% can provide homogenous fresh air distribution in the test space. No degradation in the depth of fresh air penetration was observed as the distance from the inlet window increased up to 7 m, equating to around three times the height [h] of the space. The Computational Fluid Dynamics results show that ventilation effectiveness is positively correlated with room depth and remains satisfactory (with no stagnant regions in the space) from 2h–12h for single sided, and 6h–30h for cross flow cases. These findings challenge current design guidance and refute one of the main arguments against more widespread usage of natural ventilation in the design of deeper-plan, energy efficient, and healthy buildings.