Indoor Environmental Quality & Thermal Comfort
Comfort isn't one temperature — it's six factors, and adaptation saves energy
Sustainability is for people, not just meters — and indoor environmental quality is the measurable health of the space you occupy: its light, its comfort, its quiet and its air. This unit takes on the single most expensive habit in Indian interiors: the belief that comfort means ‘22 degrees’. Thermal comfort is not one temperature; it is a balance of six factors, and the adaptive-comfort finding is that with a ceiling fan and light clothing, 29 degrees is comfortable — so a fixed low setpoint is needlessly cold and burns energy. Try it in the explorer.
Learning objectives
By the end of this lesson, you will be able to — mapped to the course outcomes for Sustainable Interior Design:
Explain indoor environmental quality as visual, thermal, acoustic and air quality, and its health effects.
Analyse thermal comfort as six factors (temperature, radiant, humidity, air movement, clothing, activity).
Use adaptive comfort — air movement and clothing widen the comfort band — to cut cooling energy.
Indoor Environmental Quality
IEQ spans visual, thermal, acoustic and air quality — poor IEQ causes sick-building syndrome. Indoor air is often dirtier than outdoor (VOCs, formaldehyde off-gassing); and ‘CFC-free’ is ozone-safe but often a high-GWP HFC, so not climate-safe.[1, 2]
IEQ is measurable health
INDOOR ENVIRONMENTAL QUALITY (IEQ) is the measurable quality of the space you actually occupy, across four dimensions: VISUAL (light and glare), THERMAL (comfort), ACOUSTIC (noise) and AIR quality. Poor IEQ is not a vague complaint — it causes headaches, fatigue and poor concentration, the cluster called SICK BUILDING SYNDROME. Good sustainable design improves health and productivity, not just energy bills; people are the point.[1]
Thermal comfort — six factors
Comfort balances six factors — air temperature, radiant temperature, humidity, air movement, clothing and activity. Air movement is cheap cooling (a fan lets you raise the setpoint), and adaptive comfort means naturally-ventilated spaces are comfortable across a much wider band.[3, 4]
Comfort is a balance
'The room needs to be 22 degrees' is a MYTH. Thermal comfort is a balance of SIX factors: air TEMPERATURE, RADIANT temperature (hot or cold surfaces around you), HUMIDITY, AIR MOVEMENT, your CLOTHING, and your ACTIVITY level. A shaded, breezy 29-degree room in light clothes can feel better than a still, humid 24-degree one. The engineer Fanger combined these into a comfort model (PMV/PPD); the point for a designer is that temperature is only one lever of six.[3]
Try it — the adaptive comfort explorer
Set a room temperature, then add a ceiling fan and lighter clothing and watch the comfort band widen upward — the same room that felt too warm at 28 degrees becomes comfortable, no colder thermostat required. That widening band is where an enormous amount of cooling energy is saved.
Adaptive comfort explorer · comfort is not one temperature
At 28°C with still air and formal clothing:
Too warmAdd air movement and lighter clothing and the comfort band widens upward — a fan makes ~29°C comfortable, so a fixed 22°C AC setpoint is needlessly cold and energy-hungry. Illustrative teaching figures, ASHRAE-55-adaptive inspired.
At a glance
| Aspect | The fact | The folklore |
|---|---|---|
| Indoor environmental quality | Measurable health — visual, thermal, acoustic, air | A vague comfort feeling |
| Indoor air | Often more polluted than outdoors (VOCs, formaldehyde) | Automatically cleaner than outside |
| 'CFC-free' | Ozone-safe, but often a high-GWP HFC — not climate-safe | Fully environmentally safe |
| Thermal comfort | Six factors (temp, radiant, humidity, air, clothing, activity) | One temperature (22 degrees) |
| Air movement | Cheap cooling — a fan lets you raise the setpoint | Irrelevant if you have AC |
| Comfort range | A wide adaptive band in naturally-ventilated spaces | One fixed setpoint for everyone |
Key terms
The measurable quality of an occupied space across visual (light/glare), thermal, acoustic and air-quality dimensions — with real effects on health, comfort and productivity.
Volatile organic compounds (including formaldehyde) released by paints, adhesives, sealants and engineered boards — the 'new' smell; specify low-VOC and ventilate.
The cluster of headaches, fatigue and poor concentration linked to poor indoor environmental quality, especially poor ventilation and air quality.
A balance of air temperature, radiant temperature, humidity, air movement, clothing and activity — not a single temperature; combined by Fanger into the PMV/PPD model.
The finding that people in naturally-ventilated buildings are comfortable across a wider temperature band because they adapt — so a fan and light clothing make far-higher temperatures comfortable.
CFC-free means ozone-safe (Montreal Protocol, 1987), but many replacements are HFCs with very high global-warming potential (phased down by the Kigali Amendment, 2016) — not the same thing.
Study task
Audit one room you use for indoor environmental quality across all four dimensions — visual (light and glare), thermal, acoustic and air — and note one improvement for each. Then use the comfort explorer to make the energy argument concretely: find the temperature at which the room is uncomfortable with still air and formal clothing, and show how a ceiling fan and lighter clothing move it back into the comfort band without lowering any thermostat. Estimate, in words, the cooling energy that adaptive habit would save over a summer — and list the two air-quality specifications (low-VOC finishes, a low-GWP refrigerant) you would insist on, explaining why ‘CFC-free’ alone is not enough.
Self-assessment
1. What are the four dimensions of Indoor Environmental Quality?
2. Why is 'the room needs to be 22 degrees' a myth?
3. What does adaptive comfort tell a designer?
4. Is a 'CFC-free' air conditioner climate-safe?
5. Why is air movement so valuable for comfort?
Recap
References & further reading
- [1]Indoor Environmental Quality — visual, thermal, acoustic and air quality; VOCs and formaldehyde; sick-building syndrome (IEQ and indoor-air references). https://www.epa.gov/indoor-air-quality-iaq
- [2]Refrigerants — Montreal Protocol (CFC phase-out, 1987) and the Kigali Amendment (HFC phase-down, 2016); global-warming potential. https://ozone.unep.org/kigali-amendment-overview
- [3]Thermal comfort — the six factors, Fanger's PMV/PPD, air movement and the comfort zone (ASHRAE 55; Koenigsberger, Manual of Tropical Housing and Building). https://www.ashrae.org/
- [4]Adaptive thermal comfort — wider comfort band in naturally-ventilated buildings (ASHRAE 55 adaptive model; adaptive-comfort research). https://www.ashrae.org/
Further reading
- Otto Koenigsberger & others, Manual of Tropical Housing and Building (Orient Longman).
- Allan Konya, Design for Hot Climates.
- C.P. Kukreja, Tropical Architecture (Tata McGraw-Hill).
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.
The author
Amogh N P
Architect, interior designer, and creative polymath. Studio Matrx began in his notebooks — his vision of design made honest, useful, and open to everyone. Its Academy is written and taught in his memory, and free, forever.
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