Modelling ventilation by means of combined mixing and displacement flow

Abstract

It is convenient to describe the ventilation of an occupied space solely by a single parameter, namely the air change rate, and to characterize air distribution as either mixing or displacement. In practice, distributions which are perfect mixing or displacement are rare, but to analyse air distribution patterns it is usually necessary to use a complex model (e.g., computational fluid dynamics), thus losing the conceptual simplicity of the mixing and displacement models. By combining the mixing and displacement models, a new two-parameter model is proposed which retains the conceptual simplicity of its parents. To the air change rate is added a displacement efficiency parameter which shows the closeness with which the air distribution approaches perfect displacement and gives an overall indication of air distribution sufficient for many applications.