PMV and PPD: Thermal Comfort Assessment According to ISO 7730

Predicted Mean Vote (PMV)

PMV predicts the average thermal sensation of a large group of people on a seven-point scale from −3 (very cold) to +3 (very hot), with 0 representing thermal neutrality. It is calculated from six input variables: four environmental (air temperature, mean radiant temperature, air velocity and relative humidity) and two personal (clothing insulation and metabolic rate).

The PMV scale is interpreted as follows:

• +3 Very hot
• +2 Hot
• +1 Warm
•   0 Neutral (optimal comfort)
• −1 Cool
• −2 Cold
• −3 Very cold

The design target for most HVAC systems is to maintain PMV between −0.5 and +0.5, corresponding to a PPD below 10 %. This range ensures that the large majority of occupants perceive the environment as thermally acceptable.

Predicted Percentage of Dissatisfied (PPD)

PPD estimates the fraction of occupants who would find the thermal environment unacceptable. Even under ideal conditions (PMV = 0) approximately 5 % of people will still feel too warm or too cold — individual variation makes it impossible to satisfy everyone. As PMV deviates from zero in either direction, PPD rises steeply: at PMV = ±1.0 about 25 % are dissatisfied, and at PMV = ±2.0 the figure reaches approximately 75 %.

In practice, achieving a PMV between −0.5 and +0.5 (PPD < 10 %) not only improves occupant satisfaction but also enhances productivity, reduces absenteeism and helps avoid energy waste from over-conditioning the space. These criteria are embedded in international standards including ISO 7730 and ASHRAE 55, making them essential tools for architects, HVAC engineers and facility managers. Computational Fluid Dynamics is often used to map PMV and PPD distributions across an entire room, identifying local discomfort zones that a single-point measurement would miss.

Recommended Comfort Requirements

ISO 7730 recommends that the PPD be kept below 10 %, which corresponds to the PMV criterion −0.5 < PMV < +0.5. The following conditions apply to spaces with light, mainly sedentary activity:

Winter conditions (heating period)

1. Operative temperature between 20 °C and 24 °C.
2. Vertical air temperature difference between ankle level (0.1 m) and head level (1.1 m) less than 3 °C.
3. Floor surface temperature between 19 °C and 26 °C (up to 29 °C for floor heating systems).
4. Mean air velocity below the limit specified for the given turbulence intensity.
5. Radiant temperature asymmetry from cold vertical surfaces (windows) less than 10 °C.
6. Radiant temperature asymmetry from a warm ceiling less than 5 °C.
7. Relative humidity between 30 % and 70 %.

Summer conditions (cooling period)

1. Operative temperature between 23 °C and 26 °C.
2. Vertical air temperature difference between ankle and head level less than 3 °C.
3. Mean air velocity below the limit specified for the given turbulence intensity.
4. Relative humidity between 30 % and 70 %.

Typical Values for Met and Clo

The metabolic rate (Met) represents the heat generated by the human body and increases with activity level. Clothing insulation (Clo) quantifies the thermal resistance provided by the occupant's clothing. The tables below list commonly used reference values for both parameters.

PMV and PPD Calculator

For projects requiring detailed thermal comfort mapping across an entire building zone, our CFD team can simulate airflow, temperature and humidity distributions and produce full PMV/PPD contour plots to identify and eliminate local discomfort zones. To learn more about the fundamentals, see our course Introduction to Computational Fluid Dynamics.