Wind tunnels test pedestrian comfort around buildings by placing a scaled physical model of the building and its surroundings inside a controlled airflow chamber, then measuring wind speeds at pedestrian height across dozens of carefully chosen points. The results show where wind conditions are acceptable and where they create discomfort or danger. Engineers then compare those measurements against recognised comfort criteria to classify each location.
Wind tunnel testing is one of two established methods for pedestrian wind comfort assessments, alongside CFD simulation. Both are widely accepted by planning authorities, and the right choice depends on the scale and nature of your project. The sections below walk through exactly how the process works, what gets measured, and how to decide which method fits your situation.
What happens inside a wind tunnel during a building test?
During a building wind tunnel test, engineers place a detailed scale model of the proposed building and its surrounding urban context inside a large enclosed chamber. A controlled airflow is generated to replicate real atmospheric wind conditions, including the way wind speed increases with height above the ground. The model is then rotated to simulate wind arriving from multiple directions, typically twelve or more compass points.
The tunnel itself is designed to reproduce what is called the atmospheric boundary layer — the natural variation in wind speed and turbulence that occurs between ground level and higher altitudes. This is achieved using roughness elements and spires at the inlet of the tunnel, which generate realistic turbulent flow before the air reaches the model.
Throughout the test, sensors measure wind speed and direction at dozens of locations around the model at pedestrian height. Each measurement point corresponds to a specific location in the real-world environment: a building entrance, a public square, a cycle path, or a street corner. The test captures how the building shape, height, and orientation redirect airflow into the surrounding space.
How is pedestrian-level wind speed actually measured in the tunnel?
Pedestrian-level wind speed in a wind tunnel is measured using small sensors placed at scaled pedestrian height around the model, typically representing 1.75 metres in real life. The most common measurement tools are hot-wire anemometers or pressure taps, which record both the mean wind speed and the fluctuating turbulent component of the flow.
Because wind is not constant in real life, the tunnel measurements capture statistical data rather than a single speed value. Engineers record the probability that wind speed exceeds a defined threshold over a given time period. These exceedance probabilities are then combined with local meteorological data — wind roses that show how often wind blows from each direction and at what speed — to produce an annual picture of conditions at each measurement point.
This combination of tunnel measurements and real-world wind statistics is what allows engineers to translate a controlled laboratory test into a meaningful prediction of what pedestrians will actually experience on site throughout the year.
What comfort and safety criteria do wind tunnel results get judged against?
Wind tunnel results are judged against comfort and safety criteria that define acceptable wind conditions for different types of outdoor activity. In the Netherlands, the applicable standard is NEN 8100, which classifies locations from Class A (best) to Class E (worst) based on how often wind speed exceeds 5 m/s at pedestrian height. For projects in the UK and internationally, the Lawson criteria serve the same purpose.
Under NEN 8100, the classification system works like this:
- Class A: wind exceeds 5 m/s less than 2.5% of the time — suitable for sitting, strolling, and walking through
- Class B: exceedance between 2.5% and 5% — still acceptable for most activities
- Class C: exceedance between 5% and 10% — borderline for sitting, poor for slower activities
- Class D: exceedance between 10% and 20% — uncomfortable for most uses
- Class E: exceedance above 20% — poor conditions for all outdoor activities
Separate from comfort, NEN 8100 also defines a wind danger threshold: locations where wind speed exceeds 15 m/s more than 0.30% of the time are classified as dangerous and generally unacceptable. Locations between 0.05% and 0.30% exceedance are considered a limited risk and may be acceptable depending on context.
The Lawson criteria used in the UK follow a similar logic but use different activity categories and thresholds. Both systems are accepted in planning and permit processes, and the choice between them typically depends on the location of the project and the requirements of the relevant authority.
How does a wind tunnel test differ from a CFD simulation?
A wind tunnel test uses a physical scale model in a controlled airflow environment, while a CFD simulation (Computational Fluid Dynamics) builds a virtual model and solves the airflow mathematically using computer software. Both methods produce equivalent results for pedestrian wind comfort assessments and are accepted by planning authorities, but they have different practical strengths.
Wind tunnel testing is particularly well suited to individual buildings and smaller masterplans where a physical model can be built and positioned accurately. It provides a direct physical representation of the building and its context, and it is the preferred method when facade pressure measurements for structural loading are also required alongside the comfort assessment.
CFD simulation, on the other hand, scales more easily to large and complex environments. A city-wide study covering thousands of buildings would be physically impractical in a wind tunnel, but entirely manageable with CFD. It also allows faster design iteration: changing the building height or orientation in a virtual model takes hours rather than days of model-making. Our CFD simulation work uses OpenFOAM with the SST k-omega turbulence model, producing colour-coded output maps that can be shared directly with clients, planners, and permit authorities.
For most building projects, the two methods are genuinely interchangeable for comfort assessments. The decision usually comes down to project scale, timeline, and whether structural loading data is also needed.
When is a wind tunnel test required instead of CFD?
A wind tunnel test is typically required instead of CFD when the project involves facade wind loading or structural pressure measurements for cladding and structural design. For comfort-only assessments, most planning authorities accept CFD as equivalent to wind tunnel testing, and the choice is left to the engineer.
There are situations where a wind tunnel remains the stronger option:
- When facade pressure coefficients are needed for structural engineering calculations under Eurocode EN 1991-1-4
- When the building has a highly irregular or complex geometry that is difficult to model accurately in CFD
- When a planning authority or client specifically requests physical testing for added confidence
- When the project is at an advanced design stage and physical validation is preferred over computational modelling
For large-scale area studies covering multiple city blocks or an entire district, CFD is generally the more practical choice. A physical wind tunnel model at that scale would be extremely difficult to build with the required accuracy, and the computational approach handles complex multi-building interactions well. Our wind engineering services cover both methods, and we advise on the right approach based on your project type and what the relevant authority expects.
What inputs are needed to commission a wind tunnel pedestrian comfort test?
To commission a wind tunnel pedestrian comfort test, you need to provide a 3D model of the proposed building, context geometry of the surrounding area (typically within a radius of 500 to 1,000 metres), and local meteorological wind data. The more complete these inputs are at the start, the faster and more accurate the assessment will be.
In practice, the key inputs are:
- Building geometry: a 3D CAD model of the proposed design, including any podium levels, setbacks, or canopies
- Surrounding context: existing and consented buildings within the study area, including their heights — this is often sourced from geodata or mapping datasets
- Meteorological data: a local wind rose showing wind frequency and speed by direction, usually sourced from a nearby weather station or a recognised dataset
- Activity programme: information about how the spaces around the building will be used — entrances, terraces, cycle routes, public squares — so the assessment focuses on the right locations
- Regulatory context: which standard applies (NEN 8100, Lawson, or another local norm) and whether the output needs to meet specific permit requirements
Early-stage designs with less geometric detail can still be assessed — simplified massing models are entirely workable for initial comfort screening. More detailed geometry is needed when the results will be submitted as part of a formal planning application. You can find an overview of what we typically need to get started on the Actiflow overview page.
How Actiflow helps with pedestrian wind comfort assessments
With over 21 years of experience in wind engineering, we carry out pedestrian wind comfort assessments for a wide range of projects: individual high-rise buildings, mixed-use developments, large masterplans, and city-wide area studies. We work with municipalities, real estate developers, architects, and structural engineers across the Netherlands, Belgium, the UK, and internationally.
Here is what working with us looks like in practice:
- Method advice from the start: we tell you whether wind tunnel testing, CFD, or a combination is the right approach for your project and what the relevant planning authority expects
- Both methods in-house: we operate our own wind tunnels in the Netherlands and the UK, and run CFD simulations on our internal HPC cluster — no subcontracting, no delays
- NEN 8100 and Lawson expertise: we produce reports that meet the specific requirements of Dutch municipalities and international planning authorities
- Clear, visual output: colour-coded comfort maps and graphics that you can share directly with clients, planners, or permit authorities without translation
- Speed and flexibility: for regular clients, we set everything aside to start the next day if needed — and our internal process automation is continuously reducing delivery times further
- Design advice, not just results: when results show wind issues, we advise on practical mitigation measures at building, facade, and public space level
Curious how we can help with your pedestrian wind comfort assessment? Feel free to contact us. We would be happy to discuss your project and help you find the right engineering solution. You can also find out more about our team and background on the about us page.
