🌿 Moderate thermal environment — the PMV and PPD indices

Environment PN-EN ISO 7730

Overview

The standard gives methods of predicting the general thermal sensation and the degree of discomfort (thermal dissatisfaction) of persons staying in a moderate thermal environment. It makes possible the analytical determination and interpretation of thermal comfort by the calculation of the PMV (predicted mean vote) and the PPD (predicted percentage of dissatisfied) and of the criteria of local comfort. It concerns healthy women and men in rooms in which thermal comfort is desired but in which there occur moderate deviations from it — in the design of new environments and in the assessment of existing ones. Worked out for the working environment, it applies also to other environments.

The PMV predicts the mean of the votes of a large group of persons on a seven-point scale of thermal sensation (+3 hot, +2 warm, +1 slightly warm, 0 neutral, −1 slightly cool, −2 cool, −3 cold), on the basis of the heat balance of the body: equilibrium occurs when the internal production of heat equals its loss to the surroundings. The PPD gives quantitatively what percentage of persons will feel the environment to be too warm or too cool — those voting "hot", "warm", "cool" or "cold" are considered dissatisfied.

The description of the method below corresponds to the edition ISO 7730:2005 (PN-EN ISO 7730:2006); in 2026 PKN introduced a new edition, PN-EN ISO 7730:2026-03, in the English version (publication date 06-03-2026; introduces EN ISO 7730:2025 and ISO 7730:2025 [IDT]; replaces PN-EN ISO 7730:2006 in all language versions together with the corrigenda Ap1:2014-02 and Ap2:2016-04 — status of the PKN card as of 23.09.2026). How the new edition differs from the one described below — WE HAVE NOT ESTABLISHED: we do not have the text of the standard. In the Polish regulations the PMV index serves also to classify thermal environments: in accordance with the regulation on the maximum admissible concentrations (NDS) and the maximum admissible intensities (NDN) the criterion for classification as a hot thermal environment is PMV ≥ +2, and as a cold one PMV ≤ −2. Thermal comfort corresponds to values within the limits −0.5 < PMV < +0.5.

SCALE OF CITATIONS — A MEASUREMENT ON THE DATABASE OF ACCREDITATION SCOPES (read on 23-09-2026, matching on the BEGINNING of the notation "PN-EN ISO 7730", i.e. the way the "Laboratories" tab of this entry searches): 208 entries at 106 laboratories.

Method principle

The PMV is calculated from the equation of the heat balance of the body, in which there occur: the metabolic rate M, the effective mechanical power W, the clothing insulation Icl and the clothing area factor fcl, the air temperature ta, the mean radiant temperature tr, the relative air velocity var, the partial pressure of water vapour pa, the convective heat transfer coefficient hc and the temperature of the surface of the clothing tcl; the equations for tcl and hc are solved iteratively (1 met = 58.2 W/m², 1 clo = 0.155 m²·K/W). The index was derived for the steady state, but it may be applied with small fluctuations of the variables if means weighted over the last hour are used. From the PMV the PPD is calculated: PPD = 100 − 95·exp(−0.03353·PMV⁴ − 0.2179·PMV²); for PMV = 0 the PPD amounts to 5 %, for PMV = ±0.5 — 10 %, for PMV = ±1 — 25 %, for PMV = +2 — 75 %.

Applications

• Assessment of thermal comfort in offices, rooms of mental work, school rooms and hospitals
• Classification of the thermal environment at the workplace (moderate / hot thermal environment PMV ≥ +2 / cold PMV ≤ −2) in accordance with the regulation on the maximum admissible concentrations and intensities
• Design and acceptance of heating, ventilation and air-conditioning installations — a check of conformity with the criteria of comfort
• Determination of the conditions which, with a given activity and clothing, give a neutral sensation (PMV = 0)
• Assessment of local discomfort: draughts, radiant asymmetry, vertical temperature gradient, floor temperature

Key parameters

Standard

Standard number

PN-EN ISO 7730:2026-03

Title (PL)

Ergonomia środowiska termicznego — Analityczne wyznaczanie i interpretacja komfortu termicznego z zastosowaniem obliczania wskaźników PMV i PPD oraz kryteriów miejscowego komfortu termicznego

Title (EN)

Ergonomics of the thermal environment — Analytical determination and interpretation of thermal comfort using calculation of the PMV and PPD indices and local thermal comfort criteria

Step-by-step procedure

1. Estimation of the metabolic rate

   Determine M in accordance with ISO 8996 or annex B of the standard, taking into account the kind of work; with a variable activity use the mean weighted by time over the previous hour.

2. Estimation of the clothing insulation

   Determine the thermal resistance of the clothing and of the chair in accordance with ISO 9920 or annex C, taking into account the season of the year.

3. Measurement of the parameters of the environment

   Measure the air temperature, the mean radiant temperature, the air velocity and the humidity in accordance with ISO 7726, at a place and at a height representative of the persons present.

4. Check of the range of application

   Make sure that the six main parameters lie within the ranges: M 46–232 W/m², Icl 0–0.310 m²·K/W, ta 10–30 °C, tr 10–40 °C, var 0–1 m/s, pa 0–2700 Pa; the index is used only for PMV from −2 to +2.

5. Determination of the PMV

   In one of three ways: (a) from the equations of the standard with a computer program (annex D), (b) from the tables of annex E for the combination of activity, clothing, operative temperature and relative velocity, (c) directly with an integrating sensor. The tables of annex E are in force for a relative humidity of 50 %; the influence of the humidity at temperatures close to comfort is small.

6. Calculation of the PPD and assessment

   Calculate the PPD from the PMV. Compare it with the criterion of comfort (−0.5 < PMV < +0.5); in the classification of a workplace check whether PMV ≥ +2 (hot thermal environment) or ≤ −2 (cold) — the methods for those environments (WBGT, IREQ) are then applied. Assess in addition the local discomfort in accordance with the criteria of the standard.

Required equipment and apparatus

Health and safety (OHS)

• The method concerns a moderate environment — with a PMV outside the range −2…+2 do not apply it to the assessment of the hazard, use the methods for a hot or a cold thermal environment
• Carry out the measurements without disturbing the work of the persons in the room; the air velocity sensors are delicate — protect them against damage

Frequently asked questions