Thermal Comfort PMV/PPD Calculator

Calculate

Indoor dry-bulb air temperature in °F

Area-weighted average temperature of surrounding surfaces in °F

Indoor relative humidity percentage (0–100%)

Local air velocity near the occupant in fpm

Total clothing thermal resistance in clo (e.g. 0.5 = light summer clothing, 1.0 = typical office winter)

Occupant activity level in met (e.g. 1.0 = seated, 1.2 = standing, 2.0 = light walking)

Overview

The Thermal Comfort PMV/PPD Calculator evaluates indoor comfort using the Predicted Mean Vote (PMV) and Predicted Percentage Dissatisfied (PPD) framework. This is the standard analytical model used to assess thermal sensation and expected dissatisfaction in moderate indoor environments. ISO 7730 specifies a method to evaluate general thermal comfort and the degree of dissatisfaction using PMV and PPD, and ASHRAE Standard 55 defines acceptable thermal environmental conditions for a substantial majority of occupants.

This matters because comfort is not determined by air temperature alone. Thermal sensation depends on air temperature, mean radiant temperature, humidity, air speed, clothing insulation, and metabolic rate. ASHRAE’s Standard 55 explicitly lists those six environmental and personal factors within scope.

This calculator is a preliminary comfort evaluation tool. It helps estimate whether the modeled condition is likely cold, cool, acceptable, warm, or hot before deeper review of local discomfort, air distribution, and real occupancy behavior. ISO 7730 also covers local discomfort criteria in addition to PMV/PPD.

How to Use This Calculator

  1. Enter air temperature – the dry-bulb temperature of the indoor air (°C or °F).

  2. Enter mean radiant temperature – the area-weighted average temperature of surrounding surfaces (°C or °F).

  3. Enter relative humidity – the indoor relative humidity (%).

  4. Enter air speed – the local air velocity near the occupant (m/s or fpm).

  5. Enter clothing insulation – the total clothing assembly thermal resistance (clo).

  6. Enter metabolic rate – the activity level of the occupant (met).

  7. Choose Imperial or Metric – select the unit system for temperature and air speed.

  8. Click “Calculate” – review PMV, PPD, and comfort category.

Typical neutral conditions: air temperature 24°C, mean radiant temperature 24°C, relative humidity 50%, air speed 0.10 m/s, clothing 0.5 clo, metabolic rate 1.1 met.

Inputs & Outputs

Inputs

  • •Air Temperature (°C / °F)
  • •Mean Radiant Temperature (°C / °F)
  • •Relative Humidity (%)
  • •Air Speed (m/s / fpm)
  • •Clothing Insulation (clo)
  • •Metabolic Rate (met)

Outputs

  • •Predicted Mean Vote (PMV)
  • •Predicted Percentage Dissatisfied (PPD) (%)

Formula

PMV/PPD Model (ISO 7730 / Fanger)

The PMV is calculated using the Fanger thermal comfort equation:

PMV = (0.303 × e^⁻⁰·⁰³⁶ᴹ + 0.028) × L

Where L is the thermal load:

L = (M − W)
    − 3.05 × 10⁻³ × [5733 − 6.99 × (M − W) − pa]
    − 0.42 × [(M − W) − 58.15]
    − 1.7 × 10⁻⁵ × M × (5867 − pa)
    − 0.0014 × M × (34 − ta)
    − 3.96 × 10⁻⁸ × fcl × [(tcl + 273)⁴ − (tr + 273)⁴]
    − fcl × hc × (tcl − ta)

Clothing Surface Temperature (tcl) — Iterative

tcl = 35.7 − 0.028 × (M − W)
      − Rcl × {3.96 × 10⁻⁸ × fcl × [(tcl + 273)⁴ − (tr + 273)⁴]
              + fcl × hc × (tcl − ta)}

PPD Equation

PPD = 100 − 95 × exp(−0.03353 × PMV⁴ − 0.2179 × PMV²)

Comfort Band Thresholds (ISO 7730 / ASHRAE 55)

Category PMV Range
COLD PMV < −1.5
COOL −1.5 ≤ PMV < −0.5
ACCEPTABLE −0.5 ≤ PMV ≤ +0.5
WARM +0.5 < PMV ≤ +1.5
HOT PMV > +1.5

ASHRAE Standard 55 uses −0.5 to +0.5 as the PMV acceptability zone for a substantial majority of occupants.

Variables

Variable Meaning Units
M Metabolic rate W/m² (= met × 58.15)
W External mechanical work W/m² (= 0 for normal activities)
ta Air temperature °C
tr Mean radiant temperature °C
pa Water vapor partial pressure Pa
fcl Clothing surface area factor —
Rcl Clothing thermal resistance m²·K/W (= 0.155 × clo)
tcl Clothing surface temperature °C (iterative)
hc Convective heat transfer coefficient W/m²·K
PMV Predicted Mean Vote —
PPD Predicted Percentage Dissatisfied %

Unit Handling

Mode Air Temperature Mean Radiant Temp Air Speed
Metric °C °C m/s
Imperial °F → converted to °C internally °F → converted to °C internally fpm → converted to m/s internally

PMV and PPD are dimensionless and identical in both unit modes.

What is Thermal Comfort PMV/PPD

PMV/PPD is a model used to estimate how a large group of occupants is likely to feel in a thermal environment. PMV predicts the average thermal sensation vote, while PPD estimates the percentage of occupants likely to be dissatisfied. ISO 7730 specifies this analytical method for moderate thermal environments, and ASHRAE Standard 55 uses a PMV-based method as one pathway for evaluating thermal comfort.

This is different from simply asking whether a room is “too hot” or “too cold.” Comfort depends on the balance between heat produced by the body and heat exchanged with the environment. Clothing, activity, air speed, humidity, air temperature, and radiant conditions all affect the result.

How PMV Works

The PMV equation integrates heat exchange from radiation, convection, evaporation, and respiration into a single thermal sensation index. What makes the model computationally iterative is the clothing surface temperature (tcl): it appears in both the radiative and convective heat exchange terms and must be solved by fixed-point iteration until convergence.

Once PMV is known, PPD follows directly from a nonlinear exponential function. The minimum PPD value under this model is approximately 5% at PMV = 0, which reflects the model’s assumption that some occupants are always dissatisfied even under neutral conditions.

This model is a population-based estimator, not an individual preference predictor. It estimates the likely average response of a large occupant group. Local discomfort — from draft, radiant asymmetry, floor temperature, or vertical stratification — requires separate evaluation under ISO 7730 and ASHRAE Standard 55.

Key Facts

  • PMV predicts the average thermal sensation of a large group of occupants, not an individual’s response.
  • Even at PMV = 0, the PPD model predicts approximately 5% dissatisfied — perfect universal satisfaction is not achievable.
  • ASHRAE Standard 55 uses −0.5 to +0.5 PMV as the acceptability zone for a substantial majority of occupants.
  • ISO 7730 also includes local discomfort criteria (draft, radiant asymmetry, floor temperature, stratification) beyond PMV/PPD.
  • Air speed has a large effect in warm conditions and is explicitly addressed in ASHRAE 55’s elevated-air-speed provisions.
  • Clothing and activity assumptions are among the largest sources of uncertainty in PMV calculations.

Applications

  • Office and classroom thermal comfort evaluation.
  • HVAC setpoint assessment and design-stage comfort screening.
  • Radiant and air-movement balance checks.
  • Preliminary standard-oriented comfort review before detailed assessment.
  • PMV/PPD comparison across design options.
  • Occupant comfort troubleshooting in existing buildings.

Example Calculation

Metric Example — Near Neutral

Given:

  • Air Temperature = 24°C
  • Mean Radiant Temperature = 24°C
  • Relative Humidity = 50%
  • Air Speed = 0.10 m/s
  • Clothing = 0.5 clo
  • Metabolic Rate = 1.1 met

Result:

PMV ≈ 0.05
PPD ≈ 5%
Category: ACCEPTABLE

Interpretation: PMV = 0.05 falls within −0.5 to +0.5. The modeled condition is close to thermal neutrality and generally aligned with typical comfort targets.

Metric Example — Slightly Warm

Given:

  • Air Temperature = 27°C
  • Mean Radiant Temperature = 28°C
  • Relative Humidity = 60%
  • Air Speed = 0.05 m/s
  • Clothing = 0.5 clo
  • Metabolic Rate = 1.2 met

Result:

PMV ≈ +0.88
PPD ≈ 21%
Category: WARM

Interpretation: PMV = +0.88 falls in the WARM band. This indicates a warm condition with elevated dissatisfaction likely unless temperature, air movement, clothing, or internal-load assumptions are adjusted.

Standards & References

Limitations

  • This calculator is a preliminary whole-body comfort estimator only.
  • It does not model local discomfort: draft, radiant asymmetry, floor temperature, vertical stratification, or transient conditions.
  • It does not account for individual preference differences, personal adaptation, or behavioral adjustment.
  • PMV/PPD is a population-based model — it does not predict individual occupant responses.
  • ISO 7730 explicitly includes local discomfort criteria in addition to PMV/PPD.
  • ASHRAE Standard 55 also distinguishes whole-body comfort from local discomfort and elevated-air-speed effects.

Common Mistakes to Avoid

  • Treating air temperature as the only comfort variable and ignoring mean radiant temperature.
  • Entering unrealistic clothing insulation values (e.g. 0 clo or 3+ clo for typical office occupants).
  • Entering unrealistic metabolic rate values (e.g. 0 met).
  • Ignoring air speed effects, especially in warmer conditions.
  • Assuming PMV near zero guarantees universal occupant satisfaction.
  • Ignoring local discomfort factors such as draft or radiant asymmetry.
  • Treating PMV/PPD output as a full substitute for field comfort evaluation.
  • Using outdoor air temperature instead of indoor air temperature.

Frequently Asked Questions

What does this calculator estimate?
It estimates whole-body thermal comfort using PMV and PPD under the stated indoor and personal conditions. PMV predicts the average thermal sensation of a large group of occupants, and PPD estimates the percentage likely to be dissatisfied.
What does PMV mean?
PMV is the Predicted Mean Vote, or the average thermal sensation expected from a large group under the modeled conditions. ISO 7730 and ASHRAE Standard 55 use PMV as a core comfort metric, with the scale running from −3 (very cold) to +3 (very hot).
What does PPD mean?
PPD is the Predicted Percentage Dissatisfied, meaning the estimated share of occupants likely to find the thermal environment unacceptable. Even at perfect PMV neutrality, PPD does not reach zero — some dissatisfied occupants are always predicted.
Is PMV between -0.5 and +0.5 usually considered acceptable?
Yes. ASHRAE Standard 55’s PMV-based method uses −0.5 to +0.5 as the key acceptability zone for thermal conditions acceptable to a substantial majority of occupants. ISO 7730 uses similar guidance for Category A and B environments.
Why can PPD still be nonzero when PMV is near zero?
The PMV/PPD model assumes some occupants will always be dissatisfied even near thermal neutrality. The minimum predicted dissatisfaction under this model is approximately 5% at PMV = 0.
Does this calculator include local discomfort?
Not fully. Draft, radiant asymmetry, floor temperature, and stratification require separate evaluation. ISO 7730 explicitly includes local discomfort criteria in addition to PMV/PPD, and ASHRAE Standard 55 also addresses local discomfort separately.
Can elevated air speed improve comfort?
Yes, especially in warmer conditions. Higher air speed increases convective heat loss from the body and can offset elevated temperature. ASHRAE Standard 55 includes elevated-air-speed provisions within its comfort framework.
Does this calculator prove compliance with a comfort standard?
No. It is a preliminary comfort estimation tool only. Final compliance depends on the exact method used, local discomfort checks, the applicable edition of the standard, and field conditions.

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