Lesson 0.2Lesson 0.2 · How to Read a Climate
What Comfort Actually Means
Comfort is not a temperature. It is a band — and the band moves with the weather, the clothes, and the body.
The 24 °C myth
The air-conditioning industry says comfort is 24 °C — everywhere, forever. But a Nagpur farmer is comfortable at 31 °C in cotton, and a Delhi grandmother is content at 19 °C wrapped in a shawl. The single magic number falls apart on contact with real people. Before you design a wall to "keep people comfortable," you have to ask the harder question: comfortable at what, and for whom?
24 °C is a chamber-test number from a cold country. Your client's body wrote a different rule — design to it.
Static versus adaptive
There are two competing models of human thermal comfort, and they lead to opposite buildings.
Static (PMV / Fanger): a fixed comfort point around 24 °C. It was built from climate-chamber tests on lightly clothed subjects in temperate countries. Its logic: seal the building and run the AC to hold the number.
Adaptive: the comfort band *rises* with the outdoor temperature. It was built from surveys of real occupants in naturally ventilated buildings. Its logic: open the building and let the body adapt.
The key finding is humbling for the compressor industry: occupants who can open a window, change their clothes, and who *expect* summer to be warm are comfortable across a far wider range than a sealed-box model predicts.
The band that slopes upward
Plot comfort temperature against the outdoor running-mean and the adaptive band climbs a gentle slope while the static AC set-point stays a flat line. The visible *gap* between them on a hot day is the cooling load that passive design exists to erase — load that, with a fan and an openable window, never had to exist at all.
The slope is the whole point: as it gets hotter outside, the temperature people actually find comfortable rises too.
Comfort isn't a dot on a thermostat. It's a band that walks uphill with the weather — and you can design to stay inside it.
Drag the weather, watch the band move
Three altitudes on the same idea
Read the band that fits you — or all three.
Don't chase 24 °C in every room. A ceiling fan, an openable window and lighter clothing genuinely shift the temperature at which you feel comfortable — often by several degrees. Air movement over your skin is worth more than a colder thermostat, and costs a fraction as much to run.
Set the comfort target from the adaptive band, not a habitual 24 °C. A naturally ventilated home in the composite or warm-humid zones can target 26–30 °C indoors with air movement — code-aligned and roughly halving the cooling load. State the comfort basis explicitly in the brief so it survives value-engineering.
The India Model for Adaptive Comfort (IMAC), naturally ventilated mode, gives T_comfort = 0.54 · T_out + 12.83 °C, with a band of ±3 °C. For Chennai at Tout = 33 °C → Tcomfort = 30.6 °C, band 27.6–33.6 °C. That relaxes the static 24 °C target by ~6.6 °C, and each 1 °C of relaxation saves roughly 6% of cooling energy.
“Adaptive comfort just means telling people to tolerate heat.”
Run the method yourself
Do the arithmetic on your own city before Module 1.
- 1Find your city's outdoor running-mean (last week's average daily temperature is a fine proxy).
- 2Compute Tcomfort = 0.54·Tout + 12.83 and the ±3 °C band.
- 3Compare that to where you'd normally set an AC — how many degrees of cooling were you about to over-engineer?
- 4List the three adaptive opportunities your room offers or lacks: openable window, fan, freedom of clothing.
↳ Use the worksheet below to record your answers.
Take it with you
A moving target is a gift
T_comfort = 0.54·T_out + 12.83) rises with outdoor temperature, so the Indian body — given a fan, a window and clothing freedom — is comfortable far above 24 °C. Each 1 °C of relaxation saves ~6% cooling energy. The band only holds with real adaptive opportunity.We now have the five climates and the moving comfort band. Module 1 hands you the instruments to measure a real site against that band — starting with the sun path over India, which governs every shading decision you will make.