Incorporating CFD Into Ventilation Design Standards to Maximise Ventilation Rates

Abstract

Ventilation is an important part of any building design and is essential for the thermal comfort of the occupants and to ensure a safe standard of air quality. Ventilation design standards have robust procedures that able to predict guidelines for ventilation rates that will lead to acceptable indoor air quality (IAQ). However, with increasing design complexity, sources of contaminants and rising energy costs, additional tools are required to refine and target these procedures. A few specialised programmes are now available to aid in the design of systems that will ensure acceptable IAQ. There is a clear trend: as the accuracy of the design tool increases, so too does the amount of source information and computing power that is required. CFD is the most detailed numerical simulation currently available. It is very effective at modelling the micro-environment in a building to determine detailed and accurate fluid flow and contaminant concentrations. In recent years CFD has been integrated with multizone models capable of modelling whole buildings. By using CFD to target key zones, and the multizone model for the remaining building, a complementary method is created. This study aims to develop a design protocol to aid with ventilation design in a low-pressure environment with high-pressure suction ports. A chemical manufacturing vendor participated in this research and was used as a case study for general model extraction (GEV) and local extraction (LEV) designs. The geometry of the manufacturing area was modelled in the ANSYS workbench with two versions of a GEV and LEV system. The suction ports were modelled at two elevations to predict airflow in the breathing zone of the workers at 1.7m and at the floor level where heavy chemical fumes may accumulate. The model was solved under a transient framework with time step and mesh independence assessments to ensure the model is robust and accurate. Time step and mesh independence testing reported accurate and reliable models. The velocity profiles in the GEV and LEV systems were reported and analysed for significant dead zones and airflow patterns. The LEV system was ultimately recommended as the preferred ventilation design system. It has significantly fewer dead zones to the GEV system with targeted extraction that results in a lower contaminant concentration overall. The vendor accepted the recommendation and built the design with positive preliminary feedback. The findings of this study suggest this could be a CFD aided design protocol for ventilation systems in low-pressure environments. Further investigation into improving computational efficiency using steady state solutions for the modelling of high complexity models, including species transport.