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comfortFoam

Overview

comfortFoam is an OpenFOAM post-processing utility that calculates thermal comfort indices according to ISO 7730:2005. It computes Predicted Mean Vote (PMV), Predicted Percentage of Dissatisfied (PPD), and Draft Rating (DR) from CFD simulation results.

Features

  • ISO 7730 Compliance: Implements the standard PMV/PPD model by P.O. Fanger
  • Draft Rating Calculation: Assesses local thermal discomfort due to air drafts
  • Regional Analysis: Support for cellSet/cellZone-based comfort evaluation
  • Volume-Weighted Averaging: Accurate spatial averaging for room-level metrics
  • Flexible Humidity Input: Compatible with various OpenFOAM solver outputs
  • Multiple Turbulence Models: Supports k-epsilon, k-omega SST, and other models
  • Advanced Radiation Handling: Compatible with various radiation models (P1, fvDOM, etc.)
  • Validation Mode: Built-in ISO 7730 validation capability
  • Parallel Computing: Full MPI parallel support for large-scale simulations

Thermal Comfort Indices

PMV (Predicted Mean Vote)

Seven-point thermal sensation scale:

  • +3: Hot
  • +2: Warm
  • +1: Slightly warm
  • 0: Neutral
  • -1: Slightly cool
  • -2: Cool
  • -3: Cold

PPD (Predicted Percentage of Dissatisfied)

Percentage of people predicted to be dissatisfied with thermal conditions:

  • PPD = 100 - 95 × exp(-0.03353×PMV⁴ - 0.2179×PMV²)
  • Minimum PPD ≈ 5% at PMV = 0

DR (Draft Rating)

Percentage of people dissatisfied due to draft:

  • DR = (34 - Ta) × (v - 0.05)^0.62 × (0.37 × v × Tu + 3.14)
  • Where Ta is air temperature, v is velocity, Tu is turbulence intensity

Installation

cd $FOAM_RUN/../HVAC-for-OpenFOAM/comfortFoam
wmake

Usage

Basic Usage

comfortFoam

Command Line Options

Option Description Default
-region <name> Specify mesh region for multi-region cases -
-cellSet <name> Calculate comfort only for specified cellSet -
-setFields <name> Alias for -cellSet <name> -
-cellZone <name> Calculate comfort only for specified cellZone -
-noWrite Calculate without writing fields false
-validate Run ISO 7730 validation mode false
-validateAirTemp <T> Air temperature for validation [°C] -
-validateRadTemp <T> Radiant temperature for validation [°C] -
-validateVelocity <v> Air velocity for validation [m/s] -
-validateRH <RH> Relative humidity for validation [%] -
-validateMet <met> Metabolic rate for validation [met] -
-validateClo <clo> Clothing insulation for validation [clo] -

Configuration File

Create a comfortFoamDict file in the constant directory:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  v2412                                 |
|   \\  /    A nd           | Website:  www.openfoam.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      comfortFoamDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

// Clothing insulation [clo]
// 1 clo = 0.155 m²·K/W
// Typical values:
// - Summer clothing: 0.5 clo
// - Light working clothes: 0.7 clo
// - Typical indoor clothing: 1.0 clo
// - Heavy suit: 1.5 clo
clo         1.0;

// Metabolic rate [met]
// 1 met = 58.15 W/m²
// Typical values:
// - Seated, quiet: 1.0 met
// - Seated, light work: 1.2 met
// - Standing, light work: 1.6 met
// - Walking slowly: 2.0 met
met         1.2;

// External work [met]
// Usually 0 for most activities
wme         0;

// Relative humidity [%]
// Used only if humidity field is not available in the case
// Range: 0-100
RH          50;

// Optional analysis region (choose only one):
// cellSet   occupiedZone;
// setFields occupiedZone;    // Alias for cellSet
// cellZone  roomA;

// ************************************************************************* //

Required Input Fields

The following fields must be present in your OpenFOAM case:

  • T (Temperature) [K] - MUST_READ
  • U (Velocity) [m/s] - MUST_READ
  • p (Pressure) [Pa] - READ_IF_PRESENT

Optional Humidity Fields

comfortFoam searches for humidity fields in this order:

  1. thermo:relHum - From buoyantHumiditySimpleFoam
  2. thermoRelHum - Legacy naming
  3. relHum - Alternative naming
  4. RH - Relative humidity [%]
  5. relativeHumidity - Relative humidity [%]
  6. Falls back to value in comfortFoamDict

Optional Turbulence Fields

For draft rating calculation:

  • k - Turbulent kinetic energy [m²/s²]
  • epsilon - Turbulent dissipation rate [m²/s³] (k-epsilon models)
  • omega - Specific dissipation rate [1/s] (k-omega SST models)
  • If not present, assumes Tu = 40% (typical for mixed convection)

Optional Radiation Fields

For accurate mean radiant temperature calculation (in order of preference):

  • G - Incident radiation field [W/m²] from radiation models
  • qr - Radiative heat flux field [W/m²] from some radiation models
  • IDefault - Default radiation intensity [W/m²/sr] from DOM models
  • If not present, uses area-weighted wall temperature

Output Fields

comfortFoam creates four fields in each time directory:

  1. PMV - Predicted Mean Vote [-3 to +3]
  2. PPD - Predicted Percentage of Dissatisfied [%]
  3. DR - Draft Rating [%]
  4. TOp - Operative Temperature [K]

Examples

Example 1: Basic comfort analysis

# Run CFD simulation first
buoyantHumiditySimpleFoam

# Calculate comfort indices
comfortFoam

# Visualize in ParaView
paraFoam

Example 2: Regional analysis

# Calculate comfort for a specific zone
comfortFoam -cellZone occupiedZone

Example 3: Multi-region case

# Calculate comfort for a specific region
comfortFoam -region indoorAir

Example 4: Parallel execution

# Decompose case for 4 processors
decomposePar -force

# Run comfort analysis in parallel
mpirun -np 4 comfortFoam -parallel

# Reconstruct fields (optional)
reconstructPar -fields '(PMV PPD DR TOp)'

Physical Parameters

Environmental Parameters

  • Air temperature: 10-30°C (50-86°F)
  • Mean radiant temperature: Assumed equal to air temperature
  • Air velocity: 0-1 m/s
  • Relative humidity: 0-100%

Personal Parameters

  • Clothing insulation: 0-2 clo
  • Metabolic rate: 0.8-4 met
  • External work: Usually 0 met

Limitations

  1. Steady-State Model: PMV/PPD assumes thermal equilibrium
  2. Uniform Conditions: Best suited for spaces with relatively uniform conditions
  3. Activity Level: Assumes constant metabolic rate
  4. Comfort Categories: For EN 15251 comfort categories, use ASHRAE55Foam

Validation

The implementation has been validated against:

  • ISO 7730:2005 reference tables
  • ASHRAE Fundamentals Handbook
  • Published PMV/PPD calculation tools

Validation Example

To verify ISO 7730 compliance:

comfortFoam -validate -validateAirTemp 22 -validateRadTemp 22 \
            -validateVelocity 0.1 -validateRH 60 \
            -validateMet 1.2 -validateClo 0.5
# Expected: PMV ≈ -0.75, PPD ≈ 17%

References

  1. Fanger, P.O. (1970). "Thermal Comfort: Analysis and Applications in Environmental Engineering"
  2. ISO 7730:2005. "Ergonomics of the thermal environment"
  3. ASHRAE Standard 55-2020. "Thermal Environmental Conditions for Human Occupancy"

Troubleshooting

Common Issues

  1. Missing humidity field: Ensure your solver outputs humidity or set RH in comfortFoamDict
  2. Out-of-range PMV: Check input parameters (clothing, activity, temperature)
  3. High DR values: May indicate excessive air velocities or temperature gradients

Debug Mode

For detailed output, modify Info statements in the source code and recompile.

Version History

  • v1.0: Initial implementation for OpenFOAM v2312
  • v1.1: Added cellSet/cellZone support
  • v1.2: Improved humidity field detection
  • v2.0: Updated for OpenFOAM v2412+
  • v3.0: Added validation mode and improved ISO 7730 compliance
  • v3.1: Enhanced turbulence model support (k-epsilon, k-omega SST)
  • v3.2: Advanced radiation field handling (G, qr, IDefault)
  • v3.3: Added full parallel computing support

Support

For issues or questions:

  • Check the GitHub repository
  • Review tutorial cases in tutorials/ directory
  • Open an issue for bugs or feature requests