Natural Ventilation Simulation Software

SimScale’s incompressible CFD and Lattice Boltzmann (LBM) solvers cover the full range of natural ventilation regimes used in building design: wind-driven cross ventilation through operable windows and façade openings; buoyancy-driven (stack effect) flow through atria, shafts, and chimneys; combined wind-and-buoyancy interaction with realistic Atmospheric Boundary Layer profiles; mixed-mode strategies that switch between natural and mechanical based on outdoor conditions; and façade-detail studies of perforated screens, louvres, and operable window angles. A 16-direction wind rose study runs in parallel on the cloud.

Buoyancy-driven ventilation, also called stack effect, arises from temperature differences between indoor and outdoor air — warmer indoor air rises and exits through high openings, drawing cooler outdoor air in through low openings. Driving pressure scales with shaft height and thermal differential. Wind-driven ventilation arises from pressure differences across the building envelope caused by wind hitting one face (positive pressure) and creating suction on the other (negative pressure), pushing air through windows and openings. Real buildings are driven by both forces simultaneously, sometimes reinforcing each other, sometimes opposing — SimScale’s CFD resolves the combined interaction explicitly.

Accurate enough that customers use it to challenge default settings in industry-standard thermal modelling tools. Greenlite Building Physics found that SimScale’s Lattice Boltzmann 16-direction wind CFD produced site-specific Cp values that differed from IES VE defaults by up to 100% in magnitude — and in some façade locations had the opposite sign — significantly changing predicted overheating, CO₂, and heating loads on a UK student accommodation project. AIRLIT studio validated buoyancy-driven flow scenarios against Lima climate data for a 9-storey university library. Fairlite Consulting independently validated CFD-derived louvre airflow within 2% of physical AS 4740 testing.

Yes — and this is where SimScale’s IES VE / EnergyPlus / DesignBuilder integration becomes load-bearing. Calibrated Cp values from CFD feed directly into CIBSE TM59 overheating assessments, ASHRAE 62.1 ventilation rate calculations, and Passivhaus energy modelling. Greenlite’s experience is that SimScale-derived Cp values “return more favourable simulation outcomes in the case of CIBSE TM59 simulations, which can return project cost savings without compromising the risk of overheating.” Architype uses SimScale to validate Passivhaus classroom natural ventilation against post-occupancy monitored data.

SimScale exports wind pressure coefficients (Cp) and detailed airflow data in formats compatible with the industry-standard dynamic thermal simulation tools used by building physics teams: IES VE, EnergyPlus, and DesignBuilder. The typical workflow is to build the thermal model in the dynamic simulation tool, run SimScale CFD for site-specific Cp values across a 16-direction wind rose, then feed those Cp values back into the thermal model — replacing the default values that whole-building tools ship with. Greenlite’s UK project documents this workflow end-to-end.