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

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.