Case Study: Virtual Testing of Louvre Performance for AS 4740:2025 Compliance in Australian Facades
- Shahram Derakhshan
- Jun 9
- 3 min read
Introduction
Louvres and ventilators are key components in building facades — enabling air exchange while protecting against wind-driven rain. In many applications, such as plantrooms, car parks, or naturally ventilated spaces, these systems must balance airflow efficiency with weather resistance.
The updated Australian Standard AS 4740:2025 provides a structured framework for assessing these products, specifically under the category of Ventilator Type 1, which refers to louvre-type ventilators. The standard evaluates their ability to permit airflow with minimal resistance and to restrict rain ingress under wind-driven conditions.
This case study explores how these performance requirements can be assessed through virtual testing using Computational Fluid Dynamics (CFD) — providing a practical pathway for design refinement and early performance validation.
Overview of AS 4740:2025 Criteria
AS 4740:2025 sets out a consistent method for evaluating the performance of Ventilator Type 1 (louvres) under defined wind and rain conditions. The standard focuses on two key aspects:
Airflow performance, measured by discharge coefficient (Cd), which reflects how efficiently air passes through the ventilator.
Rain resistance, measured by the volume of water penetration at increasing wind speeds and rainfall intensities.
The standard provides a series of performance grades — allowing products to be classified based on their effectiveness in airflow and water resistance. This supports transparent product comparison and compliance across the industry.
Technical Insight: The Importance of the Throat Area (AS 4740:2025)
In louvre systems, airflow and rain ingress are governed not just by blade angle or spacing — but by the geometry of the throat area, the internal passage where air enters, flows between blades, and exits. This zone is where the most critical pressure and velocity changes occur.
Under AS 4740:2025, airflow performance is quantified using the discharge coefficient (Cd), which reflects the ratio of actual airflow to ideal (theoretical) flow through the ventilator. The design of the throat area strongly influences this coefficient — affecting how easily air can pass with minimal resistance.
From a rain resistance perspective, the throat also becomes the pathway where wind-driven droplets may enter. The shape, surface details, and deflection angles at this point determine whether rainwater is repelled or pulled through into the interior.
High-resolution CFD modelling can resolve the flow structure in this area — including recirculation zones, turbulence, and droplet trajectories — giving designers deep insight into performance limitations and potential improvements.
CFD-Based Louvre Virtual Testing Approach
Virtual testing using Computational Fluid Dynamics (CFD) provides a flexible and detailed method for assessing louvre performance in alignment with AS 4740:2025. The simulation environment can replicate the same boundary conditions and inlet velocities used in physical test rigs, allowing for direct performance evaluation without the need for early-stage prototypes.
Key aspects of the CFD approach include:
Airflow Simulation by CFD
The airflow is modelled through the full ventilator geometry, including the throat area, to calculate pressure drop and estimate the discharge coefficient (Cd). This helps verify whether the ventilator meets airflow performance classes defined in the standard.
Rain Penetration Modelling by CFD
Wind-driven rain is introduced at standardised speeds and rainfall rates, tracking droplet behaviour to estimate water ingress. CFD allows for visualising splash, deflection, and drainage mechanisms that affect performance under storm conditions.
Geometry and Blade Design Effects
Subtle design variations — including blade angle, spacing, curvature, and casing details — can be assessed quickly to identify their impact on airflow efficiency and water protection.
By combining airflow and rain simulations, the CFD process enables designers and manufacturers to evaluate multiple design options virtually, significantly reducing development time and physical testing costs.
Conclusion and Practical Implications
AS 4740:2025 offers a well-defined and transparent benchmark for assessing the performance of louvre-type ventilators used in Australian buildings. Its focus on airflow efficiency and rain resistance enables suppliers, designers, and façade engineers to specify and compare products with greater confidence.
While traditional compliance methods rely on physical prototyping and lab testing, virtual assessment using CFD provides a faster, cost-effective alternative that supports early-stage optimisation. This is especially valuable in project scenarios with custom louvre designs, space constraints, or architectural integration challenges.
At Deratec, we specialise in applying practical CFD simulations to building performance challenges. Our modelling approach is calibrated to match the intent and boundary conditions of AS 4740:2025 — helping louvre manufacturers and façade consultants streamline their design process and reduce reliance on trial-and-error testing.
Interested in virtual testing for your next project?
Visit www.deratec.com.au or get in touch to discuss how we can support your product development or specification work using simulation-based evidence.
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