Modelling of contaminant dispersion in underfloor air distribution systems: comparison of analytical and CFD methods

ABSTRACT

Underfloor air distribution (UFAD) systems are known to provide thermal comfort and good indoor air quality (IAQ) at relatively low energy cost. The aim of this paper is to develop an analytical model to predict the vertical CO₂ distributions inside contaminated thermal plumes and in the surrounding air in UFAD spaces. The 2D model is based on thermal plume and turbulent fountain theory and it accounts for CO₂ convective transport as well as vertical and lateral diffusion. The proposed space model consists of four horizontal layers delimited by three critical heights: the air density interface, the supply jet throw height and the plume terminal height. The model predictions of lumped layer CO₂ concentrations compared well with the results produced by computational fluid dynamics (CFD) simulations for different ventilation rates and heat loads. The analytical model can be put into practice to give recommendations on UFAD preliminary design and acceptable IAQ.

KEYWORDS:

• Underfloor air distribution
• space model
• thermal plume model
• turbulent fountain model
• contaminant dispersion
• CFD modelling