Thermal Comfort
When a space feels right — and why it's adaptive.
Comfort is not a single temperature — it is a balance between the heat your body makes and the heat it can shed, shaped by six factors. And in a naturally-ventilated building it adapts: the comfortable temperature rises with the outdoors, which is why a fan and an open window keep an Indian room comfortable far beyond a sealed office's 24 °C.
Learning objectives
By the end of this lesson, you will be able to — mapped to the course outcomes for Climatology & Building Physics:
Explain the body's heat balance and how it loses heat.
List the six factors of thermal comfort.
Use the adaptive model to estimate a neutral temperature and comfort band.
Explain why comfort is adaptive in naturally-ventilated buildings.
What comfort depends on
The body sheds metabolic heat by convection, radiation, evaporation and conduction; comfort depends on six factors — air temperature, mean radiant temperature, humidity, air velocity, clothing and activity — and in NV buildings the neutral temperature tracks the outdoors.[4, 5]
The body as a heat engine
The body must shed its metabolic heat to hold ~37 °C: by convection to moving air, radiation to surrounding surfaces, evaporation of sweat, and a little conduction. Evaporation is the only path that still works when the air is hotter than the skin — which is why air movement matters so much in the heat.[4]
Adaptive comfort
Enter the outdoor running-mean temperature to find the neutral temperature and the 80% comfort band: Tn = 0.31 × Tout + 17.8 °C.[5]
Adaptive comfort calculator
Neutral temperature for a naturally-ventilated building (ASHRAE 55): Tn = 0.31·Tout + 17.8.
At a glance
| Aspect | One | The other |
|---|---|---|
| Comfort model | Static: fixed setpoint (~22–24 °C), sealed HVAC | Adaptive: Tn rises with outdoor temp, NV buildings |
| Factor type | Environmental: air temp, MRT, humidity, air velocity | Personal: clothing (clo), activity (met) |
| Heat loss in the heat | Convection/radiation fail as air nears skin temp | Evaporation still works — needs air movement |
| Humidity effect | Low RH: evaporative cooling effective | High RH: evaporation blocked, comfort harder |
| Air movement | Still air: comfort ceiling lower | ~1 m/s air: offsets ~2–3 °C of warmth |
Key terms
Body heat output per area; 1 met = 58.2 W/m² (seated rest).
Clothing insulation; 1 clo = 0.155 m²·K/W (≈ a business suit).
The area-weighted mean temperature of the surfaces around you.
Air speed over the skin; raises convective + evaporative cooling — the fan effect.
An index combining air temperature, humidity and air movement into one.
Olgyay's plot of a comfort zone and the measures that extend it.
Model where the neutral temperature rises with outdoor temperature in NV buildings.
The operative temperature at which occupants feel neither warm nor cool.
Think it through
Use the calculator for an outdoor mean of 30 °C, then 20 °C. How far does the comfortable temperature move? Explain why a fixed 24 °C air-conditioning setpoint wastes energy in a naturally-ventilated Indian building.
Self-assessment
1. The adaptive neutral-temperature formula (ASHRAE 55) is —
2. The only body heat-loss path that still works when the air is hotter than the skin is —
3. Which is NOT one of the six factors of thermal comfort?
Recap
References & further reading
- [1]V. Olgyay, Design with Climate: Bioclimatic Approach. Princeton University Press.
- [4]O.H. Koenigsberger et al., Manual of Tropical Housing and Building. Orient Longman.
- [5]ANSI/ASHRAE Standard 55 — Thermal Environmental Conditions for Human Occupancy. ASHRAE.
- [6]S. Manu, Y. Shukla, R. Rawal et al., India Model for Adaptive Comfort (IMAC). Building & Environment (2016).
Further reading
- B. Givoni, Man, Climate and Architecture. Elsevier.
- S.V. Szokolay, Introduction to Architectural Science. Routledge.
- V. Olgyay, Design with Climate. Princeton University Press.
Sources gathered and fact-checked June 2026. Published values vary by source, sample and method — treat as indicative and confirm against the cited standard before structural use.