Explain PMV and PPD and their role in thermal comfort.

• A. PMV predicts the energy required to heat the building; PPD predicts cooling load.
• B. PMV predicts the average thermal sensation; PPD predicts the percent dissatisfied; designs aim for PMV near 0.
• C. PMV and PPD are about acoustic comfort.
• D. PMV is a project management metric; PPD is a project progress date.

Answer: (B)

PMV and PPD are design tools that quantify how people perceive indoor temperature. PMV, or Predicted Mean Vote, estimates the average thermal sensation of a group on a scale from cold to hot (-3 to +3) under specific conditions, taking into account factors like metabolic rate, clothing, air temperature, mean radiant temperature, air velocity, and humidity. PPD, or Predicted Percentage Dissatisfied, translates that same condition into the portion of people who would be unhappy with the environment. In practice, designers aim for a PMV near zero, which corresponds to the smallest expected level of dissatisfaction, typically resulting in a low PPD. These concepts come from Fanger’s thermal comfort model and are most reliable in steady indoor environments; they aren’t about energy use, acoustics, or project-management metrics.