Glass-roof comfort — Atrium.

Understanding the comfort challenges in large volumes

Spaces of high architectural value but thermally complex

Atriums, reception halls and high-rise spaces are distinguished by their generous volumes, their largely glazed walls and their direct link with the outside. This transparency, a source of light, also becomes a major technical constraint: the solar gains, the stratification of the air masses and the thermal inertia of the structures continuously alter the comfort balance.

Warm air tends to accumulate in the upper part while the glazed walls absorb and release the radiation in rapid cycles — creating temperature gradients that are difficult to compensate for with a static approach.

The dominant phenomena: radiation, stratification and inertia

The solar radiation constitutes the main source of incident energy: it passes through the glazing, turns into heat on contact with the surfaces, then radiates towards the occupants. The thermal stratification superimposes air layers of different temperatures (differences of several degrees between floor and glass roof). The thermal inertia of the materials dampens the variations but can release the accumulated heat late, prolonging the discomfort.

Understanding these phenomena requires a dynamic approach, capable of reproducing the reciprocal exchanges between convection, conduction and radiation.

The EOLIOS approach: modelling the indoor climate

CFD simulation, a multi-physics analysis tool

EOLIOS relies on computational fluid dynamics (CFD) to reproduce the interactions between the air, the surfaces, the heat and the radiation. The 3D models simultaneously solve the conservation equations of mass, momentum and energy, offering a complete reading of the thermo-airflow behaviour: velocities, pressures, transfers by convection and radiation, stagnation zones and temperature imbalances.

Solar radiation and climatic scenarios

EOLIOS integrates real weather data and the position of the sun to simulate direct, diffuse and reflected radiation, taking into account the solar factor of the glazing, the shading of the façades and the spectral behaviour of the materials. The radiation-convection coupling makes it possible to calculate the mean radiant temperature, an essential parameter of the perceived feeling. The simulations cover several extreme scenarios — hot summer, cold winter, mid-season.

Comfort assessment through the PMV and PPD indices

Beyond temperatures and velocities, EOLIOS relies on the standardised indicators PMV (Predicted Mean Vote) and PPD (Predicted Percentage of Dissatisfied) of the ISO 7730 standard. The PMV quantifies the thermal sensation (–3 to +3), the PPD estimates the percentage of dissatisfied, taking into account the air temperature, the radiant temperature, the air velocity, the humidity, the activity and the clothing. Objective: to tend towards a neutral comfort (PMV ≈ 0, PPD < 10 %).

From diagnosis to climate strategy

The CFD analysis reveals the mechanisms behind the imbalances: recirculation zones, poorly mixed volumes, hot spots linked to localised solar gains. EOLIOS then formulates targeted strategies — adjusting the position of a supply vent, modifying a diffusion angle, reviewing the control. In high-rise halls, the control of the air mixing is central: a subtle balance between velocity (discomfort if too fast) and homogeneity (stratification if insufficient).

The solar gains are characterised for different representative regimes, leading to control recommendations: adaptation of the supply flow rate, modulation of the cooling floor, solar protections.

Hybrid strategies: supply, draught and natural ventilation

EOLIOS studies the potential of natural ventilation and night free-cooling: the density differences between warm and cold layers generate a natural thermal draught that can be exploited to remove the heat accumulated during the day. Combined with intelligent mechanical control, this allows high-performing hybrid strategies: night natural ventilation, assisted supply during the day, modulation of the opening vents according to the wind.

Predictive comfort and assisted design

The simulation makes it possible to observe the building before it is built: a genuine virtual laboratory where the architectural and technical choices are tested, compared and optimised. The 3D mappings of temperature, velocity and pressure validate and adjust the design (orientation of the nozzles, flow rates, supply temperature, solar factor of the glazing), reducing the uncertainties linked to great heights.

In the EOLIOS approach, comfort becomes a central performance criterion, integrated from the sketch stage — guaranteeing thermal stability and energy performance whatever the operating mode.