Review of tracer gas-based methods for the characterization of natural ventilation performance: Comparative analysis of their accuracy

Abstract

Natural ventilation systems, taking advantage of natural driving forces, help to reconcile energy efficient buildings with a good Indoor Air Quality (IAQ). Its efficiency depends on several factors including climatic regions, seasons, building configurations, and surrounding characteristics. Building regulations often prescribe minimum airflow, which promotes the implementation of mechanical ventilation systems in new constructions. Their performance is invariant and easily verifiable making them convenient. Increasing incentives towards building energy sobriety encourage the use of natural or hybrid ventilation systems in new buildings. However, the lack of a measurement protocol often prevent from justifying that those systems verify air change requirements. It partially explains their weak implementation in new constructions. The purpose of this paper consists in establishing a literature review concerning the measurement of natural airflows. The literature review allowed identifying tracer gas methods, including also occupant-generated CO2 methods, as being widely used methods to assess natural ventilation. Tracer gas methods allow the measurement of natural airflows, as well as indicators related to air distribution, without interfering with the flow pattern. After describing those methods, this paper discusses their suitability towards the measurement of natural airflows. They either rely on assumptions whose violation impact their accuracy, or practical limitations prevent from in-situ measuring. For instance, some methods, which are widely used in natural ventilation, assume steady airflows during the measurement. Some innovative protocols, also based on tracer gas principles are also reported. Some insights are given towards an increase of the reliability of tracer gas methods.