Thermal Comfort — PMV and PPD Models

Predicted Mean Vote (PMV) and Predicted Percentage Dissatisfied (PPD) for indoor thermal comfort.

thermalcomfortpmv

Overview

Thermal comfort is defined as the condition of mind that expresses satisfaction with the thermal environment (ASHRAE 55). The most widely used model is the PMV-PPD model by Fanger (ISO 7730).

PMV Scale

PMV	Sensation
+3	Hot
+2	Warm
+1	Slightly warm
0	Neutral
−1	Slightly cool
−2	Cool
−3	Cold

The target for comfort: $-0.5 < PMV < +0.5$

PPD — Predicted Percentage Dissatisfied

$PPD = 100 - 95 \cdot \exp\left(-0.03353 \cdot PMV^4 - 0.2179 \cdot PMV^2\right)$

8 rows

PMV vs PPD relationship
pmv
-2
-1.5
-1
-0.5
0
0.5
1
1.5

Source: ISO 7730

Factors Affecting PMV

Factor	Variable	Typical Office Value
Air temperature	$T_a$	22–24 °C
Mean radiant temp.	$T_r$	≈ $T_a$
Air velocity	$v_a$	< 0.2 m/s
Relative humidity	$RH$	40–60%
Metabolic rate	$M$	1.2 met (seated office)
Clothing insulation	$I_{cl}$	0.5–1.0 clo

Note: Even at PMV = 0, at least 5% of occupants will be dissatisfied — this is the minimum possible PPD.

Source: engineeringtoolbox.com