What is Indoor Environmental Quality?
Indoor environmental quality (IEQ) describes conditions inside a building that affect occupant health, comfort, and productivity — air quality, thermal comfort, lighting, and acoustics. Architects and engineers design ventilation, daylighting, and materials to optimize it.
Indoor environmental quality (IEQ) is the overall condition of air quality, thermal comfort, lighting, and acoustics inside a building, measured and managed through ventilation rates, temperature/humidity control, daylighting, and low-emission materials.
- •Adequate outdoor air ventilation rate
- •Stable thermal comfort (temperature + humidity)
- •Sufficient daylight and glare control
- •Low background noise, good acoustics
- •Low-VOC materials and finishes
- •Insufficient fresh air, elevated CO2
- •Overheating or excessive cold, high humidity
- •Glare or inadequate lighting
- •High noise, poor speech intelligibility
- •High-VOC materials causing off-gassing
Try it: interactive calculator
Step-by-step worked examples
A classroom holds 25 students (Pz=25) in an 80 m² room (Az=80). Using Rp=3.8 L/s·person and Ra=0.3 L/s·m² (ASHRAE-style values), find the required outdoor airflow.
Vbz = Rp·Pz + Ra·Az Vbz = 3.8×25 + 0.3×80 Vbz = 95 + 24 Vbz = 119 L/s
The same classroom's HVAC only delivers 90 L/s. What's the shortfall and likely IEQ symptom?
Shortfall = 119 − 90 = 29 L/s Under-ventilation raises indoor CO2 and reduces fresh air per person Likely symptoms: drowsiness, poor concentration, stuffy air
If occupancy drops to 15 students (same room), recalculate the required airflow.
Vbz = 3.8×15 + 0.3×80 Vbz = 57 + 24 Vbz = 81 L/s (below the 90 L/s HVAC capacity — now adequate)
Flashcards
Quick quiz
Q1.Which of these is NOT typically part of IEQ?
Q2.In Vbz = Rp·Pz + Ra·Az, the Ra·Az term accounts for…
Q3.Rp=2.5 L/s·person, Pz=20, Ra=0.3 L/s·m², Az=50 m². Find Vbz.
Q4.Elevated indoor CO2 concentration typically indicates…
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Common mistakes
IEQ is only about air quality. — Correct: IEQ also includes thermal comfort, lighting, and acoustics — not air quality alone.
More ventilation is always better regardless of energy cost. — Correct: Ventilation must be balanced against energy use; codes like ASHRAE 62.1 define minimum adequate rates, not unlimited maximums.
CO2 itself is the main health hazard indoors. — Correct: CO2 is mainly a ventilation-adequacy proxy; the real concerns are VOCs, particulates, humidity, and pathogen dilution alongside comfort.
Good daylighting has no connection to IEQ. — Correct: Daylight access and glare control are core components of IEQ, affecting mood, alertness, and visual comfort.
FAQ
What is indoor environmental quality (IEQ)?
IEQ describes the conditions inside a building — air quality, thermal comfort, lighting, and acoustics — that affect occupant health and comfort.
What is the formula for required ventilation (IEQ air quality)?
ASHRAE's breathing zone formula: Vbz = Rp·Pz + Ra·Az, combining a per-person rate and a per-area rate.
What are examples of IEQ factors?
Fresh air ventilation rate, temperature and humidity control, daylight and glare, low-VOC materials, and background noise level.
How do you calculate required outdoor air for a room?
Multiply the per-person outdoor air rate by occupancy, multiply the per-area rate by floor area, and add the two results (Vbz = Rp·Pz + Ra·Az).