Glossary
PMV (Predicted Mean Vote)
Plain-Language Definition
A thermal comfort index predicting the average response of a large group of people on a 7-point scale from -3 (cold) to +3 (hot), where 0 represents thermal neutrality.
Technical Context
Developed by P.O. Fanger, PMV is calculated from six variables: air temperature, mean radiant temperature, air velocity, relative humidity, metabolic rate (met), and clothing insulation (clo). ASHRAE Standard 55 recommends PMV between -0.5 and +0.5 for acceptable thermal comfort. ISO 7730 uses PMV to define three comfort categories: A (PMV +/-0.2), B (PMV +/-0.5), C (PMV +/-0.7). The WELL Building Standard v2 requires PMV monitoring in occupied spaces.
Why It Matters
Thermal comfort directly impacts occupant productivity, health, and satisfaction. Research shows a 2% decrease in productivity per degree deviation from optimal temperature. PMV provides a scientific basis for setting HVAC parameters rather than relying on subjective complaints. It is the primary metric used by ASHRAE 55, ISO 7730, and WELL v2.
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