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HVAC / Thermal Comfort
Thermal Comfort PMV/PPD Simulator (ISO 7730)
Compute Fanger's PMV and PPD in real time from air temperature, mean radiant temperature, air velocity, humidity, clothing insulation and metabolic rate. Evaluate office HVAC, residential air-conditioning and healthcare-facility comfort against the ISO 7730 / ASHRAE 55 categories in a single view.
Parameters
Air temperature t_a
°C
Mean radiant temperature t_r
°C
Radiant temperature from walls, windows and ceiling (measured with a globe thermometer)
Clothing surface temperature t_cl is solved iteratively. f_cl = clothing area factor, h_c = convective heat transfer coefficient.
Indoor Thermal Comfort — Fanger PMV / PPD (ISO 7730)
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I hear "PMV" all the time in HVAC discussions — how is it different from just the room temperature? Is this why a room labelled 25 °C can feel either too cold or too hot?
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Exactly right. What humans feel as "hot" or "cold" isn't decided by air temperature alone — it's actually six variables. On the physical side: (1) air temperature t_a, (2) radiant temperature t_r from walls and windows, (3) air velocity v, (4) humidity RH. On the human side: (5) clothing insulation in clo, (6) metabolic rate in met. For example at 25 °C, sitting by a sunlit wall heated to 35 °C feels uncomfortably warm from radiation, but a 0.5 m/s breeze from a fan suddenly feels cool. Fanger at Denmark Technical University collapsed all six variables into a single number — that's PMV.
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I see. With the defaults — 24 °C, 1.0 clo (winter suit), 1.2 met (office) — PMV came out to about 0.79. Isn't that "slightly warm"? Does it mean a winter suit at 24 °C is already too warm?
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Yes, and that's the interesting part of the Fanger model. A winter suit (1.0 clo) at 24 °C does shift PMV toward warm. Try dropping clothing to 0.5 clo (summer wear) — PMV drops sharply toward 0. That's exactly why Japan's "Cool Biz" policy recommends 28 °C in summer with no jacket: reducing clothing lets you reach the same comfort at a higher set point, cutting cooling energy dramatically.
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PPD is "predicted percentage of dissatisfied" — but you said even at PMV = 0 there are 5% dissatisfied. What does that mean? Shouldn't an ideal environment satisfy everyone?
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That's the clever part of Fanger's work. The equation was fit to data from 1,300 subjects, and no matter how perfectly you tune PMV = 0, around 5% always vote "too cold" or "too warm". People have different basal metabolism, sweat rates, and that day's condition. An environment that satisfies everyone is physically impossible. HVAC pros call this the "complainer floor" — designing to PPD < 10% means 90%+ are satisfied and the remaining 10% will complain no matter what. Once PPD passes 20%, meeting rooms get noticeably restless.
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The PPD-vs-PMV curve forms a clean V shape. At ±2 about 80% are dissatisfied. So in practice you keep PMV within ±0.5?
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That maps directly to the ISO 7730 categories. Cat A (|PMV| ≤ 0.2, PPD ≤ 6%) is the highest standard — operating rooms, VIP meeting rooms. Cat B (≤ 0.5, ≤ 10%) is the standard for general offices. Cat C (≤ 0.7, ≤ 15%) is acceptable for energy-priority operation. Buildings chasing LEED or WELL certification target A–B; Europe's EN 16798 uses the same framework, and Japan's CASBEE adopts it too. In design you aim for Cat B and try not to drop to Cat C even during peak hours.
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One more thing — when I raise the air velocity to 1.0 m/s, PMV drops dramatically. Does that mean turning down the AC and adding a fan saves energy?
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Absolutely. Raising velocity from 0.1 to 0.8 m/s lowers perceived temperature by 2–3 °C. So 28 °C with a fan feels about the same as 26 °C with no air movement. Bumping the set point by 2 °C saves 15–20% of cooling energy, so ceiling-fan + HVAC is now an iron rule of energy-efficient design. The catch is local draft — a strong jet hitting the neck or feet causes discomfort. ISO 7730 Annex A defines a separate "draft rate DR" index for that, which you ideally use alongside PMV.
Frequently Asked Questions
PMV (Predicted Mean Vote) is a seven-point index from -3 (cold) to +3 (hot) that predicts the average thermal sensation of a group, while PPD (Predicted Percentage of Dissatisfied) is the percentage of people likely to vote uncomfortable in the same environment. PPD is derived from PMV by PPD = 100 - 95·exp(-0.03353·PMV⁴ - 0.2179·PMV²). A key feature of the model is that even at PMV = 0 (neutral), PPD never drops below 5% — a perfectly comfortable environment for everyone is physically impossible.
Category A is the highest standard with |PMV| ≤ 0.2 and PPD ≤ 6%, used for operating rooms and premium hotel suites where complaints must be minimised. Category B is the recommended standard with |PMV| ≤ 0.5 and PPD ≤ 10%, applied to typical offices and meeting rooms. Category C is the acceptable level with |PMV| ≤ 0.7 and PPD ≤ 15%, used for energy-priority buildings or transport facilities where some dissatisfaction is tolerated. This tool reports the category automatically.
Metabolic rate: seated quiet 1.0 met (58.15 W/m²), office work 1.2 met, slow walking 2.0 met, light exercise 3.0 met, jogging 4.0 met. Clothing: nude 0 clo, summer wear (short-sleeve shirt + light trousers) 0.5 clo, long-sleeve shirt + slacks 0.7 clo, winter business suit 1.0 clo, heavy coat 1.5 clo, arctic outfit 2.5 clo. At the same air temperature, 24 °C with 1.0 clo and 24 °C with 0.5 clo produce very different PMV values.
Proposed by de Dear & Brager (1998), the adaptive model is an empirical alternative for naturally ventilated buildings. Fanger's PMV assumes a sealed, mechanically conditioned space, but in naturally ventilated buildings occupants adapt through window opening and clothing adjustments, producing a wider acceptable indoor temperature band that correlates with outdoor temperature. For example, with a monthly mean outdoor temperature of 25 °C, the acceptable operative temperature is 25.5 °C ± 3.5 °C (80% acceptable). The adaptive model is standardised in ASHRAE 55 and EN 16798-1 and is widely used for energy-efficient summer operation and mixed-mode buildings.
Real-World Applications
Office HVAC design and commissioning: Major design firms target PMV that does not exceed +0.5 during peak cooling load nor fall below -0.5 during heating. Combined with BEM software like Revit MEP or IES VE, an 8,760-hour annual simulation evaluates the share of hours achieving PPD ≤ 10% — often required to exceed 95% as a KPI. Predicted PMV at design time and post-occupancy complaint rates correlate strongly, which is why the Fanger model has been the industry standard for over forty years.
LEED, WELL and CASBEE certifications: Thermal comfort is invariably part of building environmental certifications. LEED EQ "Thermal Comfort" credit requires compliance with ASHRAE 55 (effectively PMV/PPD), the WELL Comfort Concept requires PPD ≤ 10% for 98% of the year for higher tiers, and CASBEE awards full marks for PMV within ±0.5 in its "Q1 Indoor Environment" category. Because these certifications directly affect real-estate value and rents, precise PMV/PPD simulation is performed from the earliest design phase.
Quantitative basis for Cool Biz / Warm Biz: Japan's MoE-recommended "28 °C in summer, 20 °C in winter" comes from PMV analysis. With summer 0.5 clo, 1.2 met and v = 0.2 m/s at 28 °C, PMV ≈ +0.4 (Cat B), while winter 1.0 clo at 20 °C gives PMV ≈ -0.2 (Cat A) — theoretically justified balance points between energy savings and comfort. The same framework underpins Europe's "winter set point 19 °C" (IEA) and Singapore's office recommendation of 24–26 °C.
Coupling with CFD analysis: After room airflow and temperature distribution are analysed with OpenFOAM, ANSYS Fluent or STAR-CCM+, computing PMV at each mesh point and mapping the result is now common practice. Non-uniform PMV directly under diffusers, near cold windows or above local jets becomes visible and feeds back into diffuser placement and cold-radiator countermeasures. Modelica and EnergyPlus also ship standard PMV blocks for building-control optimisation (model predictive control, MPC).
Common Misconceptions and Pitfalls
The biggest trap is judging thermal comfort by air temperature alone. Japan's Building Standard Law allows a broad 17–28 °C indoor range, but that's a simplistic regulation that ignores PMV and often diverges from reality. A window-side desk in direct sun can read 25 °C air with a 32 °C mean radiant temperature, pushing PMV beyond +1. In winter, near a cold pane, the air may be 22 °C but radiant temperature drops to 15 °C, dragging PMV down to -0.7. Most complaints of "I lowered the set point and it's still hot" or "I raised it and it's still cold" come from overlooked radiant temperature. Measuring radiation with a globe thermometer or thermal imager is step one of any HVAC design.
Second, using PMV outside its applicable range. Fanger's PMV assumes steady-state, mechanically conditioned, sealed spaces (offices, residences, retail). Naturally ventilated buildings, sports facilities, outdoor terraces, and rooms with violent temperature swings show large prediction errors — especially in hot, humid conditions (PMV > +1.5). It's important to use complementary indices such as the Standard Effective Temperature (SET*) or the Adaptive Thermal Comfort model. Also, elderly people, infants, and patients with thermal disorders have different heat balances from healthy adults, so direct PMV application can miss hypothermia or heatstroke risk.
Finally, ignoring local discomfort from drafts and temperature non-uniformity. PMV predicts whole-body average sensation, but local discomforts — cold airflow on the neck (draft), vertical temperature gradient between feet and head, cold floors — need separate evaluation. ISO 7730 Annex A defines additional criteria for "draft rate DR", vertical air-temperature difference, floor temperature, and radiant asymmetry. PMV = 0 with one of these violated produces stubborn complaint patterns. In real surveys, nearly every case of "PMV says OK but complaints don't stop" can be traced to local discomfort. Always check supply jet patterns, cold radiator profiles, and underfloor-supply temperatures alongside PMV.
How to Use
Enter air temperature (°C) between 10–30°C; typical office setpoint is 21–23°C
Set mean radiant temperature (°C) accounting for window/radiator proximity; for indoor spaces without radiant asymmetry, use air temperature ±2°C
Input air velocity (m/s): still indoor air ~0.1 m/s, near ventilation outlet ~0.3–0.5 m/s
Specify relative humidity (%) between 30–70%; 45–55% is typical office target
Define clothing insulation (clo) and metabolic rate (W/m²): sedentary office work = 1.0 clo and 58.2 W/m² (1 met)
Execute calculation to obtain PMV (−3 to +3 scale), PPD percentage, and ISO 7730 compliance category (A/B/C)
Worked Example
Conference room at 22°C air temperature, 22°C mean radiant temperature, 0.15 m/s air velocity, 50% relative humidity, occupants wearing 1.0 clo (business casual), light activity 70 W/m² (1.2 met). Simulator calculates: clothing surface temperature t_cl = 31.5°C, convective heat transfer h_c = 3.8 W/m²K, radiant loss = 45.2 W/m², PMV = +0.15, PPD = 5.1%. Result satisfies ISO 7730 Category A (PMV between −0.5 and +0.5, PPD <10%).
Practical Notes
Mean radiant temperature dominates comfort when surfaces differ from air; window-adjacent seating requires 1–3°C adjustment downward in winter
Relative humidity below 30% increases evaporative losses; above 65% reduces skin moisture evaporation efficiency—stay within 40–60% for offices
Air velocity >0.25 m/s causes draft discomfort even if PMV favorable; use local shielding or desk placement away from diffusers