How to Simulate HVAC System using OpenFOAM

How to Simulate HVAC System using OpenFOAM

ARTICLES

Wiratama

11/27/20253 min read

How to Simulate HVAC Systems with OpenFOAM: Complete Beginner-to-Advanced Guide

Simulating HVAC (Heating, Ventilation, and Air Conditioning) systems with OpenFOAM allows engineers to analyze airflow distribution, temperature gradients, contaminant transport, ventilation efficiency, and thermal comfort inside buildings or mechanical spaces. While commercial tools like ANSYS Fluent or Star-CCM+ are often used in industry, OpenFOAM provides a powerful open-source alternative that is fully customizable.

This article explains the full workflow of running HVAC simulations using OpenFOAM — from geometry preparation to post-processing.

1. Define Your HVAC Simulation Objective

Before opening OpenFOAM, clarify the purpose of the analysis:

  • Airflow distribution inside a room

  • Ventilation effectiveness (ACH, age of air, CO₂ dispersion)

  • Temperature distribution (thermal comfort)

  • Pressure drop in ducts

  • HVAC diffuser performance

  • Data center cooling efficiency

  • Contaminant / smoke transport

Typical HVAC simulations involve turbulent and incompressible airflow, often with thermal coupling.

2. Prepare the Geometry

Create the geometry using CAD tools:

Simplify the model:

  • Remove bolts, screws, tiny fillets

  • Keep smooth, watertight surfaces

  • Represent diffusers and grilles accurately

Export the geometry as STL.

Your exported STLs are still in a single surface geometries, you can manage and separate them by using specialized STL editor for OpenFOAM, tCFD-Pre.

3. Mesh the Domain

You can mesh in:

  • snappyHexMesh (OpenFOAM built-in)

  • cfMesh

  • external meshing tools (Pointwise, Salome, etc.)

For HVAC:

  • Use hexa dominance for stability

  • Add refinement around diffusers, obstacles, and HVAC vents

  • Keep mesh non-orthogonality low

  • Use boundary layers for accurate wall modeling

Typical mesh sizes: 1–10 million cells

4. Select the Appropriate OpenFOAM Solver

HVAC simulations may involve airflow, heat transfer, and sometimes species transport. Choose based on physics:

A. For Airflow Only (Isothermal)

Use:

  • simpleFoam (steady-state, incompressible)

  • pimpleFoam (transient, incompressible)

B. For Airflow + Heat Transfer

Use:

  • buoyantSimpleFoam (steady-state or transient with large time-steps, buoyant)

  • buoyantPimpleFoam (transient with small time-steps buoyant)

These account for:

  • temperature

  • density-driven airflow

  • thermal stratification

C. For CO₂ / Contaminant Transport

Add scalar transport:

  • passiveScalarFoam

  • reactingFoam (if needed)

5. Set Up Boundary Conditions

Typical HVAC boundaries include:

Inlets (Diffusers or Supply Air)

  • Type: fixedValue for velocity

  • Velocity magnitude: based on diffuser specs

  • Temperature: supply air temperature

  • Turbulence: ( k ), ( \omega ), or turbulence intensity

Outlets (Return Air)

  • Type: pressure outlet

  • Zero gradient for velocity

Walls

  • No-slip wall

  • Thermal BC options:

    • fixed temperature

    • heat flux (q)

    • convective heat transfer

Furniture / Obstacles

  • Treated as solid walls

  • Optional heat generation

6. Choose Turbulence Model

For typical HVAC rooms or data centers:

  • k–ε (robust, widely used in ventilation CFD)

  • k–ω SST (better near-wall performance)

  • RNG k–ε (good for indoor airflow)

For high-quality indoor flow predictions:
Use RANS first, then LES if needed.

7. Run the Simulation

Use commands like:

blockMesh

snappyHexMesh -overwrite simpleFoam

or for thermal simulations:

buoyantSimpleFoam

For transient:

pimpleFoam

8. Post-Process in ParaView

Use ParaView to visualize:

  • Airflow streamlines

  • Temperature gradients

  • Velocity vectors

  • Pressure distribution

  • Contaminant dispersion

To export high-quality images from ParaView:

File → Save Screenshot → set resolution → Save

9. Validate the Simulation

Validation methods:

  • Compare with ASHRAE guidelines

  • Compare air velocity with diffuser datasheets

  • Compare temperature field with field measurements

  • Compare pressure drops with ducting standards

10. Best Practices for HVAC Simulations in OpenFOAM

  • Use refined mesh near supply vents

  • Set realistic boundary conditions from HVAC equipment specs

  • Start with steady-state, then shift to transient

  • Use LES for detailed contaminant tracking

  • Use CO₂ as tracer gas to evaluate ventilation effectiveness

Conclusion

Simulating HVAC systems with OpenFOAM is a powerful way to analyze indoor airflow and thermal comfort at a professional level. With the right solver, mesh strategy, and thermal boundary conditions, OpenFOAM can match the capabilities of commercial CFD tools—while offering full customization for advanced R&D.

If you want to simulate your HVAC project on OpenFOAM, but dont have time to learn the complex OpenFOAM user experience, please try tensorHVAC-Pro, a dedicated GUI of OpenFOAM for HVAC application.

tensorHVAC-Pro is a dedicated HVAC flow and thermal simulation software, Intuitive and Easy to use, designed for HVAC engineers - not CFD expert. Learn more..

tensorHVAC-Pro

Read more articles..

Blog