A simplified approach to describe complex diffusers in displacement ventilation for CFD simulations

With the capability to improve indoor air quality while simultaneously reducing energy demand, displacement ventilation is becoming popular. However, the numerical simulation of air distribution in an indoor space with displacement ventilation using computational fluid dynamics (CFD) is challenging because of the complexity of air diffuser geometry and the complicated airflow pattern generated. Typical air diffusers used for displacement ventilation systems include, but are not limited to, quarter-circular-perforated, grille, floor-perforated, and swirl diffusers. None of them can be treated as a simple opening in CFD simulations because their effective area ratios are small. We have developed a new, simple method to describe those diffusers by directly specifying the correct jet momentum from the diffusers while adjusting the airflow rate by changing the effective areas. This is done by setting some CFD cells for a diffuser with a certain momentum, while other cells are randomly blocked. By implementing this method into a commercial CFD program, this study used the method to simulate air distributions in an office and a workshop with those diffusers under cooling or heating conditions. The distributions of air velocity, temperature, and airborne contaminant concentration are in good agreement with the corresponding experimental data obtained from an environmental chamber.

This paper presents a simplified method for description of complex diffusers in computational fluid dynamics simulation of displacement ventilation at high computational efficiency. It may be used to assist the design and analysis of air distribution for displacement ventilation as well as other types of ventilation with complex diffusers.