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, 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 4740:2000.

Synergetics used CFD to examine a number of louvre designs for rain resistance and air flow pressure drop in order to allow classification in accordance to AS/NZS 4740:2000. This was achieved by creating a digital twin model of the apparatus defined in the standard which allows comparable tests under multiple flow conditions. Regulatory authorities accepted the classification of the louvres derived from the CFD models permitting both a dramatically reduced time to market and increased confidence in designs without requiring multiple, expensive, prototypes.

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