CFD For Classifying Ventilation Louvres to AS 4740:2000

Figure 1: The air velocity distribution through Rain Resistance test chamber during testing.

Ventilation requirements for commercial buildings specify fresh air supply rates. Fresh air is drawn into an active ventilation system through louvres and grills which are exposed to all weather conditions including wind driven rain. A challenge for fresh air louvre designs is to operate with low air flow resistance but also prevent rain entering the building causing mould, corrosion, and odours. The performance of louvres is classified by “AS/NZS 4740:2000 – Natural ventilators – Classification and performance”. Depending on the application, louvres will require a particular rating for rain and air flow resistance.

Figure 2: An assessment of raindrop paths, showing they arrive at the louvre but do not penetrate into the ventilation system duct work. No leakage of rain represents a Class A design for Rain Resistance in accordance with AS/NZS 4740:2000.

Synergetics used CFD to analyse various louvre designs for rain resistance and air flow pressure drop. This was done to classify them according to AS/NZS 4740:2000. We created a digital twin model of the apparatus in the standard to conduct comparable tests under different flow conditions. Regulatory authorities accepted the CFD-derived classification. This acceptance significantly reduced the time to market and increased confidence in the designs without the need for multiple, expensive prototypes.

We have used the same methodology for many louvre designs, both as an assessment rating tool and to optimize designs.

For further examples of CFD for buildings see our sector page.