Air exchange efficiency of a ventilation system - A case study

Abstract

The problems associated with poor indoor air quality may in most cases be attributed to poorly designed and poorly performing ventilation systems. The problems in a mechanically air-conditioned building are compounded if the building is fairly air tight and depends on fresh air provision at the central fresh air intake in the air handling unit (AHU). The performance of such a ventilation system not only depends on the quantity of fresh air provided at the fresh air intake but the manner in which this air is distributed around the various zones in the building. The ventilation performance, characterised by the space air distribution, may be dictated by either the initial design and commissioning of the different components of the air-conditioning system, such as the AHU, ducts, diffusers, etc. or subsequent changes in the office space layout and furnishing. This paper deals with the determination of some key ventilation parameters such as the air change rate, the age of air and the air exchange efficiency, all of which lead to an insight into the performance of the ventilation system. The approach is case-study-based and the methodology involves tracer gas analysis employing the concentration decay method as a means of determining the key parameters.