Trial / Demo
MacroFlo within IES VE was used to move natural ventilation design from what was forecasted to happen, to real proof points. This included sizing components, validating indoor air quality, and providing the real figures needed to secure innovative low-energy solutions on two French primary school renovation projects.
Modelling natural ventilation in real buildings
Natural ventilation is an established bioclimatic strategy, but it’s rarely quantified with the precision needed to satisfy building control bodies, reassure clients, or make confident sizing decisions. That’s why for two primary school renovations, Groupe Scolaire Saint Jérôme Susini in Marseille, and Groupe Scolaire des Ormeaux in Fontenay-aux-Roses this project was so unique.
For MAYA Construction Durable, a sustainable design consultancy specialising in bioclimatic approaches, the goal on both projects was not simply to apply natural ventilation principles, but to demonstrate with real figures, the strategies would deliver air renewal and indoor air quality under actual climatic and occupancy conditions.
Classrooms with 25 to 30 children are environments where CO₂ can build up quickly, and where the consequences of inadequate ventilation, for both health and concentration, are significant. In Marseille, the design needed to exploit a wind-prone Mediterranean climate and managing the variability that comes with it. In Fontenay-aux-Roses, the system relies entirely on stack effect and wind pressure, with no mechanical extract assistance or fans, a decision that reduces energy consumption and maintenance costs, but one demands rigorous validation before partners and control bodies will accept it.
Two strategies, one platform: How MacroFlo supported both projects
At Marseille, the single-flow natural ventilation strategy supplies fresh air through motorised inlets above window frames, with extraction via stack effect through vertical ducts terminating in roof chimneys. Motorised dampers open during occupied periods and close when the building is unoccupied to limit unnecessary heat loss. One or two vertical ducts are provided per room depending on its air renewal requirement.
IES VE's MacroFlo module was used to model the combined effect of wind pressure on the external walls and stack effect in the duct columns, sizing the air inlets, vertical ducts, and transfer grilles for each space. Simulation of a north-facing first-floor classroom on 10 February demonstrated that CO₂ levels, which rise with occupancy during the morning, return almost to unoccupied levels during the lunch break, with no accumulation building up across the day, confirming that the strategy meets indoor air quality targets without requiring mechanical assistance.
At Fontenay-aux-Roses, the double-flow strategy uses Kingspan WindCatcher® units on the top floor and ExStream E Series natural counter-flow heat exchangers on the ground and first floors. The vertical risers carry no wind cowls and no mechanical extract fans, and the system relies entirely on stack effect and wind pressure at the air inlets.
IES VE's precise geometric model of the building and its surrounding obstructions, combined with annual wind-rose analysis, was essential in understanding how prevailing winds interact with the building form. The results confirmed that the south-east wind, perpendicular to the façade inlets, adds to the stack effect and increases air renewal, and air renewal rates are directly correlated with both wind speed and wind direction across the year. Over 1,910 simulated occupied hours, CO₂ remained below 1,000 ppm in 100% of hours across all seven classrooms, and below 800 ppm for between 80% and 88% of occupied hours depending on the room.
The evidence that secures innovative solutions
“For MAYA Construction Durable, IES VE serves a dual purpose on projects of this type. It is a design optimisation tool, enabling duct sizes, inlet positions, and damper control strategies to be iterated and refined against real climatic data before anything is built.
And it’s also a validation tool too, because it offers the ability to present building control bodies and clients with actual airflows and CO₂ concentrations, rather than ventilation principles alone. This is what gives sceptical partners the confidence to accept natural ventilation as a credible, low-energy alternative to mechanical systems. The flexibility of MacroFlo's scenario parameters that included occupancy patterns, damper schedules, opening configurations, seasonal and diurnal conditions, gives the design team the freedom to understand the physical behaviour of natural ventilation across the full range of conditions a building will encounter across a typical year, rather than designing to a single peak condition that may not reflect real-world performance.
For a consultancy working across climates as different as coastal Mediterranean and Île-de-France, that breadth of applicability is what makes IESVE a reliable foundation for defending and delivering its bioclimatic design approach.”
Max Maurel, Director, MAYA Construction Durable
