Quantifying Comfort
Thermal comfort is deceptively complex — it depends on air temperature, radiant temperature, humidity, air movement, clothing, and physical activity, all interacting simultaneously. In 1970, P.O. Fanger at the Technical University of Denmark published a landmark model that combines these six factors into a single Predicted Mean Vote (PMV) on a -3 to +3 scale. His work, based on experiments with over 1300 subjects, remains the foundation of all modern thermal comfort standards.
The Heat Balance Equation
The human body is a heat engine that must maintain core temperature near 37°C. Metabolic heat production (from food metabolism and muscular work) must be balanced by heat losses through radiation, convection, evaporation, and respiration. The PMV model calculates this balance: when losses equal production, PMV is zero (neutral). When the body retains heat, PMV is positive (warm); when it loses too much, PMV is negative (cool).
The PPD Curve
Even at perfect thermal neutrality (PMV = 0), Fanger found that 5% of people remain dissatisfied — human thermal preference has inherent variability. The PPD curve shows that maintaining PMV between -0.5 and +0.5 keeps dissatisfaction below 10%, which is the target specified by ASHRAE Standard 55 and ISO 7730. Outside this range, dissatisfaction rises sharply: at PMV = ±2, over 75% of occupants are uncomfortable.
Practical Applications
Building HVAC systems are designed and controlled to maintain thermal comfort. The PMV model guides thermostat setpoints, humidity control strategies, and air distribution design. In offices (1.0-1.2 met, 0.5-1.0 clo), the comfort zone is typically 20-26°C depending on season. This simulation lets you explore how each parameter shifts the comfort perception and identify which environmental adjustments most effectively restore comfort.