HVAC-for-OpenFOAM

Advanced HVAC simulation toolkit for OpenFOAM, providing specialized solvers and utilities for humidity modeling, thermal comfort analysis, and indoor climate assessment according to international standards (ISO 7730, ASHRAE-55, UTCI).

Features

Core Capabilities

• Humidity Transport Modeling: Full integration of humidity physics into OpenFOAM's thermophysical framework
• Thermal Comfort Analysis: Comprehensive comfort metrics (PMV, PPD, UTCI, ASHRAE-55)
• Solar Radiation Integration: Support for EPW weather data and OpenFOAM's native solar models
• Buoyancy-Driven Flows: Specialized solvers for natural and mixed convection with humidity effects
• Building Physics: Advanced boundary conditions for multi-layer walls with thermal mass
• Wind-Driven Rain: Lagrangian particle tracking for rain droplet impingement

Components

CFD Solvers

• buoyantHumidityPimpleFoam: Transient solver for buoyant, turbulent flow with humidity transport
• buoyantHumiditySimpleFoam: Steady-state solver using SIMPLE algorithm
• buoyantBoussinesqPimpleDyMFoam: Dynamic mesh solver for Boussinesq approximation
• windDrivenRainFoam: Wind-driven rain simulation with multiple droplet phases

Comfort Analysis Tools

• comfortFoam: ISO 7730 thermal comfort (PMV, PPD, Draft Rating)
• UTCIFoam: Universal Thermal Climate Index calculator
• ASHRAE55Foam: ASHRAE Standard 55 compliance analysis
• ISO7243Foam: ISO 7243 WBGT heat stress assessment
• ISO7933Foam: ISO 7933 heat strain screening
• AoAFoam: Age of Air calculation for ventilation assessment

fvOptions

• thermostatSource: Thermostat-controlled heating source with proportional regulation, sensor placement, and supply temperature limiting (Vorlauf)

Boundary Conditions

• buildingElementBC: Advanced thermal boundary condition for building walls with multi-layer support
• heatFluxRadiation: Lumped wall-temperature boundary condition with prescribed total power, optional qr coupling, and temperature limits for radiative HVAC loads

Libraries

• humidityRhoThermo: Thermophysical model extension for humidity calculations
• solarCalculator: Solar position and radiation calculations

Documentation

Solver Documentation

• buoyantHumidityPimpleFoam - Transient humidity solver
• buoyantHumiditySimpleFoam - Steady-state humidity solver
• humidityRhoThermo - Humidity thermophysical library
• windDrivenRainFoam - Wind-driven rain simulation

Comfort Analysis Tools

• comfortFoam - ISO 7730 comfort metrics
• UTCIFoam - UTCI calculation with weather data support
• ASHRAE55Foam - ASHRAE-55 adaptive comfort model
• ISO7243Foam - ISO 7243 WBGT post-processing
• ISO7933Foam - ISO 7933 heat strain screening

fvOptions

• thermostatSource - Thermostat-controlled heating with sensor and Vorlauf limit

Boundary Conditions

• buildingElementBC - Multi-layer wall boundary condition with radiation

Additional ThermoTools Patch Set

This repository also contains an additional thermoTools patch tree at:

• src/thermoTools/

The patch currently adds:

• heatFluxRadiation: a patch-temperature boundary condition for cases that need a prescribed total power (for example occupants or equipment) while allowing the surface temperature to react to convection and radiation
• temperature guards for externalWallHeatFluxTemperature via the optional entries minTemperature and maxTemperature

heatFluxRadiation

heatFluxRadiation is intended for single-region cases where fixedValue is too restrictive, but externalWallHeatFluxTemperature in mode flux/power with kappaMethod fluidThermo can drive the patch temperature to unphysical values.

The model advances a single patch temperature from a lumped energy balance:

m Cp dT/dt = Q + integral(q dA) + Qrad - Qconv

with:

• Q: prescribed total power input in W
• q: optional prescribed heat flux in W/m^2
• Qrad: integrated contribution from the optional qr field
• Qconv: heat loss to the adjacent fluid based on the local patch gradient

Example:

person
{
    type            heatFluxRadiation;
    kappaMethod     fluidThermo;
    Q               constant 60;
    mass            8;
    Cp              3500;
    qr              qr;
    qrRelaxation    0.7;
    relaxation      1.0;
    minTemperature  280;
    maxTemperature  320;
    value           uniform 304.15;
}

For area-based cooling or heating loads, q can be prescribed directly:

floor
{
    type            heatFluxRadiation;
    kappaMethod     fluidThermo;
    q               uniform -20;
    mass            500;
    Cp              900;
    qr              qr;
    value           uniform 295.15;
}

Validation cases for the boundary condition are provided under:

• src/thermoTools/derivedFvPatchFields/heatFluxRadiation/validation/prescribedQr
• src/thermoTools/derivedFvPatchFields/heatFluxRadiation/validation/fvDOMParallelPlates

prescribedQr validates the pure qr source term against an exact first-step balance. fvDOMParallelPlates validates the coupled fvDOM + heatFluxRadiation response against the black parallel-plates solution, with the radiative flux appearing in time 1 and the patch temperature update in time 2.

Temperature Guards for externalWallHeatFluxTemperature

externalWallHeatFluxTemperature now also supports:

• minTemperature
• maxTemperature

These bounds are intended as a numerical safeguard when a strongly negative qr or a very small effective conductivity would otherwise drive the patch temperature below physically meaningful values.

Example:

wall
{
    type            externalWallHeatFluxTemperature;
    mode            flux;
    qr              qr;
    q               uniform 0;
    qrRelaxation    0.7;
    relaxation      1.0;
    kappaMethod     function;
    kappaValue      constant 0.2;
    alphaValue      constant 1e-7;
    minTemperature  250;
    maxTemperature  350;
    value           uniform 299.15;
}

OpenFOAM-v2512 Patch Set

This repository contains a ready-to-copy patch tree for OpenFOAM v2512 at:

• OpenFOAM-v2512/src/parallel/distributed/distributedTriSurfaceMesh/
• OpenFOAM-v2512/src/thermophysicalModels/radiation/

The patch extends solar radiation handling for partially transparent surfaces (0 < t < 1) by:

• enabling transmissivity from transparent boundary radiation properties
• propagating ray transmissivity through solarLoad face shading
• scaling direct and reflected solar load contributions consistently
• clipping distributed ray-search segments to processor-local bounds

To apply in an OpenFOAM-v2512 source tree, copy the matching files from this folder into the OpenFOAM source and rebuild the affected OpenFOAM libraries with wmake.

Technical Details

Humidity Modeling

The humidity transport is integrated into OpenFOAM's thermophysical framework through:

• Extended equation of state with humidity effects
• Humidity-dependent thermophysical properties
• Custom boundary conditions (e.g., fixedHumidity)
• Fields: relative humidity, specific humidity, water vapor partial pressure

Comfort Calculations

All comfort tools follow established standards:

• ISO 7730: Fanger's PMV/PPD model with local draft rating
• ISO 7243: WBGT-based heat stress assessment
• ISO 7933: Heat strain screening based on required evaporation
• UTCI: 6th-order polynomial approximation with radiation effects
• ASHRAE-55: Adaptive comfort model for naturally ventilated spaces

Applications

• HVAC system design and optimization
• Indoor air quality assessment
• Natural ventilation design
• Building energy simulation with dynamic thermal mass
• Urban microclimate studies
• Thermal comfort evaluation
• Compliance checking with international standards
• Building facade performance analysis
• Rain penetration and moisture risk assessment

License

This project is licensed under the GNU General Public License v3.0 - see the LICENSE file for details.