Thermal Comfort (PMV/PPD) Calculator

What is the PMV/PPD Thermal Comfort Model?

The Predicted Mean Vote (PMV) model, developed by P.O. Fanger and standardized in ISO 7730, predicts the average thermal sensation of a large group of people on a 7-point scale from -3 (cold) to +3 (hot), with 0 being neutral. It combines six factors: air temperature, mean radiant temperature, air velocity, relative humidity, metabolic rate (met), and clothing insulation (clo).

Predicted Percentage Dissatisfied (PPD) is derived from PMV and indicates the percentage of people expected to be thermally uncomfortable. Even at PMV=0 (neutral), PPD is 5% because individual variation means some people are always uncomfortable. ISO 7730 Category B (typical offices) requires -0.5 ≤ PMV ≤ +0.5, corresponding to PPD < 10%.

Metabolic rate is expressed in met (1 met = 58.2 W/m², seated at rest). Typing is ~1.1 met, standing work ~1.6 met, and heavy labor ~3-4 met. Clothing insulation is in clo (1 clo = 0.155 m²·K/W, typical business suit). Summer clothes ≈ 0.5 clo, winter indoor ≈ 1.0 clo.

Formula: PMV = f(Ta, Tr, v, RH, M, Icl) PPD = 100 - 95 × exp(-0.03353 × PMV⁴ - 0.2179 × PMV²)

Example Calculation

Office conditions: air temperature 23°C, mean radiant temperature 22°C, air velocity 0.1 m/s, relative humidity 50%, metabolic rate 1.1 met (typing), clothing 0.9 clo (business casual). PMV ≈ -0.2 (slightly cool). PPD ≈ 6%. This falls within ISO 7730 Category A (PMV ±0.2, PPD < 6%) — excellent comfort conditions.

When to Use This Calculator

• HVAC engineers verifying that design conditions (temperature, humidity, air velocity) will achieve acceptable thermal comfort for building occupants
• Facility managers investigating thermal comfort complaints to identify which environmental parameter (temperature, radiant heat, draft) is causing dissatisfaction
• Workplace health professionals assessing whether thermal conditions in offices, factories, or server rooms meet ISO 7730 comfort categories
• Researchers studying indoor environmental quality as part of post-occupancy evaluation or building performance certification (WELL, LEED)
• Choosing between comfort and heat-stress assessment — use this ISO 7730 PMV/PPD model for moderate indoor comfort; for hot environments where heat-related illness is the risk, use the WBGT heat stress calculator (ISO 7243)

Common Mistakes to Avoid

• Using air temperature alone as a comfort metric — radiant temperature from cold windows or hot equipment can shift PMV by 1-2 units even when air temperature is ideal
• Ignoring clothing and metabolic rate — a seated office worker (1.0 met, 0.7 clo) has completely different comfort requirements than a standing warehouse worker (2.0 met, 1.0 clo)
• Assuming one temperature satisfies everyone — even at PMV=0, 5% are dissatisfied; providing personal control options (fans, heaters, adjustable layers) is more effective than chasing a single setpoint
• Neglecting air velocity in mechanically ventilated spaces — cold drafts from diffusers positioned above occupied zones are the most common source of local discomfort complaints

How to Interpret Results

• If PMV is between -0.5 and +0.5 (PPD < 10%), the space meets ISO 7730 Category B — acceptable for most commercial buildings
• If PMV is between -0.2 and +0.2 (PPD < 6%), the space meets Category A — the highest standard for premium office environments
• If PMV is below -1.0, occupants will perceive the space as cool/cold — increase air temperature, reduce air velocity, or increase radiant temperature
• If PMV is above +1.0, occupants will perceive the space as warm/hot — reduce air temperature, increase air movement, or reduce radiant heat sources

Related Standards & References

• ISO 7730 — Ergonomics of the thermal environment — Analytical determination and interpretation of thermal comfort using PMV and PPD
• ASHRAE 55 — Thermal Environmental Conditions for Human Occupancy
• EN 16798-1 — Indoor environmental input parameters for design and assessment of energy performance
• WELL Building Standard — Thermal Comfort feature requirements

Frequently Asked Questions

Why do people in the same room feel differently about temperature?

Individual thermal comfort varies due to differences in metabolism, body composition, clothing, activity level, age, and acclimatization. The PMV model predicts the average group response — even in optimal conditions (PMV=0), 5% of people will be dissatisfied. Personal control (desk fans, adjustable layers) is the most effective way to accommodate individual differences.

How does air velocity affect thermal comfort?

Increased air velocity enhances convective and evaporative heat loss from the body. At temperatures below neutral, drafts cause discomfort (cold sensation). Above neutral, moderate air movement (0.2-0.5 m/s) can offset 2-3°C of excess warmth. ISO 7730 limits mean air velocity to 0.15 m/s in winter and 0.25 m/s in summer to prevent draft complaints.