Predicted Mean Vote (PMV) & Predicted Percentage Dissatisfied (PPD): Thermal Comfort Indices for ISO 7730

Predicted Mean Vote (PMV) & Predicted Percentage Dissatisfied (PPD): Thermal Comfort Indices for ISO 7730 (dimensionless)

Apply the PMV/PPD calculator alongside the clo insulation guide to map clothing, activity, and environmental inputs into actionable comfort targets.

Model Overview and Conceptual Foundations

Fanger’s heat balance approach

PMV predicts the average thermal sensation vote of a large group of occupants on the seven-point ASHRAE scale (−3 cold to +3 hot). Developed by P.O. Fanger in the 1960s, the model balances metabolic heat production, mechanical work, and heat exchanges via convection, radiation, evaporation, and respiration. Inputs include metabolic rate (met), clothing insulation (clo), air temperature, mean radiant temperature, air velocity, and water vapour pressure. Solving the heat balance yields skin temperature and sweating rate, which translate to a PMV value.

Link to Predicted Percentage Dissatisfied

PPD quantifies the expected proportion of occupants dissatisfied with thermal conditions. Empirically derived from laboratory studies, the relationship is PPD = 100 − 95·exp(−0.03353·PMV⁴ − 0.2179·PMV²). Even at PMV = 0 (neutral), PPD equals 5%, acknowledging that individual preferences vary. Designers therefore aim for PMV between −0.5 and +0.5 to keep PPD below 10%, aligning with ISO 7730 Category B environments.

Historical Context and Standardisation

Laboratory origins and validation

Fanger’s experiments at the Technical University of Denmark involved climate chambers with controlled temperature, humidity, and air movement. Participants wearing specified clothing ensembles performed defined activities, enabling Fanger to calibrate heat transfer coefficients and validate the PMV equation. Subsequent studies across Europe and North America confirmed the model’s applicability to office environments, paving the way for international adoption.

Inclusion in international standards

ISO 7730 and ASHRAE Standard 55 codified PMV/PPD criteria for building design and operation. ISO 7730 defines categories (A, B, C) with specific PMV and PPD ranges, while ASHRAE Standard 55 provides analytical and graphical compliance methods. These documents reference supporting quantities—clo, met, operative temperature—that are detailed in related explainers within this Units and Measures collection.

Equations, Parameters, and Computational Considerations

Solving the heat balance

The PMV model solves for surface temperature (t_cl) using iterative methods because convective heat transfer coefficient h_c depends on air velocity and the temperature difference between clothing surface and ambient air. Once t_cl is known, convective, radiative, and evaporative heat losses are computed to satisfy the heat balance. Numerical algorithms in tools like the PMV/PPD calculator automate this process, enabling rapid scenario analysis for design charrettes and commissioning workflows.

Input uncertainty and sensitivity

Small deviations in inputs can shift PMV significantly. For example, increasing clothing insulation by 0.2 clo or air velocity by 0.1 m/s can alter PMV by ~0.2 units. Sensitivity analyses help facility managers prioritise control strategies—tightening thermostat deadbands, adjusting diffuser layouts, or providing personal comfort devices. Moisture control, discussed in the wet-bulb article, stabilises vapour pressure inputs that influence evaporative heat loss terms.

Measurement and Field Implementation

Instrumentation requirements

ISO 7726 specifies instruments for measuring air temperature, mean radiant temperature, humidity, and air speed. Globe thermometers estimate mean radiant temperature, while anemometers capture low air velocities typical in offices. Occupant clothing and activity levels must be documented, referencing clo and met tables like those in the clo explainer.

Commissioning and continuous monitoring

During commissioning, engineers compare measured conditions with model predictions to verify HVAC performance. Continuous monitoring integrates sensor networks and analytics dashboards that compute PMV/PPD in real time. When humidity spikes elevate PMV, facility teams may deploy the dehumidifier payback calculator to justify equipment upgrades that restore comfort margins.

Applications and Emerging Trends

Building design and operations

Architects and engineers use PMV/PPD to size HVAC systems, design façades, and evaluate adaptive comfort strategies. Integrating PMV with envelope performance metrics from the R-value article ensures that insulation and glazing choices support targeted comfort categories. Post-occupancy evaluations compare measured comfort votes with PMV predictions to fine-tune control sequences.

Transportation and specialised environments

Automotive and aerospace industries adopt PMV/PPD to assess cabin comfort under varying loads and solar exposures. Hospitals and laboratories apply PMV while balancing infection control airflow requirements. For mixed-mode buildings, operators compare PMV with adaptive comfort models and outdoor metrics such as the Heat Index article to coordinate natural ventilation strategies during heat waves.

Human-centric and personalised comfort

Emerging research extends PMV to account for individual factors—age, metabolic differences, and personal control preferences. Wearable sensors and machine learning models adjust PMV inputs dynamically, offering personalised comfort predictions. Integrating thermal data with lighting metrics via the room lighting calculator supports holistic human-centric design.

Key Takeaways

PMV/PPD quantify thermal sensation and dissatisfaction using a heat balance approach validated in climate chamber studies.
ISO 7730 and ASHRAE Standard 55 embed PMV/PPD limits into building design categories, linking comfort to occupant well-being.
Accurate inputs—temperature, radiation, humidity, air speed, clothing, and activity—are essential for reliable predictions.
Field implementation couples instrumentation with analytics to maintain comfort in offices, vehicles, and specialised facilities.
Emerging personalised comfort systems extend PMV/PPD frameworks with adaptive controls and occupant feedback.