Contaminant stratification in displacement ventilated spaces - a two zone model approach. Model prediction compared to experimental data

Displacement ventilation (DV) is an alternative to conventional mixing ventilation in various types of rooms. DV is superior to mixing ventilation when it comes to removing contaminants and surplus heat in a room if designed and applied correctly. In the design process of a space with DV it is necessary to have design methods and simulation tools that can predict the vertical contaminant stratification that arise.
In this paper, both steady state and transient models for prediction of contaminant stratification are proposed. The models are based on a two-zone approach, where also a model for the entrainment of clean air in the human boundary layer is included. Sub-models for convective air flow rates and boundary layer air flow in the rooms are also included. The proposed models can be used for design of displacement ventilation and for evaluation of different ventilation efficiency indices.
Predictions from the model have been compared to measurements in fourteen empirical cases found in the literature. The evaluation of the two contaminant models (steady state and transient) is promising for most of the variables compared. However, experimental results for indices measuring air quality in the inhalation zone is better than the predicted values. This under-prediction is conservative if the models are to be used for design of DV and determining necessary ventilation air flow rates.