What Indoor Environmental Quality Means
Indoor Environmental Quality (IEQ) encompasses four dimensions of the indoor environment that directly affect occupant health, comfort, and productivity: air quality, thermal comfort, lighting, and acoustics. People spend approximately 90% of their time indoors — the quality of that environment has measurable impacts on cognitive performance, absenteeism, and wellbeing.
The Four Dimensions of IEQ
| Dimension | Key Parameters | Primary Standard |
|---|---|---|
| Indoor Air Quality (IAQ) | CO₂, PM2.5, PM10, VOCs, formaldehyde, ventilation rate | ASHRAE 62.1, WELL v2 |
| Thermal Comfort | Temperature, humidity, air velocity, radiant temperature, PMV/PPD | ASHRAE 55, ISO 7730 |
| Lighting | Illuminance (lux), uniformity, glare, daylight, colour temperature | IES, EN 12464-1 |
| Acoustics | Background noise (NC/NR), speech privacy, reverberation time | ASHRAE Handbook, WELL Sound concept |
Key IEQ Metrics and Thresholds
| Parameter | Good Practice | Acceptable | Poor / Red Flag | Source |
|---|---|---|---|---|
| CO₂ (indoor) | ≤ 600 ppm above outdoor | ≤ 800 ppm total | > 1,200 ppm | ASHRAE 62.1, WELL |
| PM2.5 (indoor) | ≤ 10 μg/m³ | ≤ 15 μg/m³ | > 35 μg/m³ | WELL, WHO |
| PM10 (indoor) | ≤ 20 μg/m³ | ≤ 50 μg/m³ | > 100 μg/m³ | WHO |
| Total VOCs | ≤ 200 μg/m³ | ≤ 500 μg/m³ | > 1,000 μg/m³ | WELL, EN 16798 |
| Formaldehyde | ≤ 27 ppb | ≤ 50 ppb | > 100 ppb | WELL, WHO |
| Temperature (office) | 22–24°C | 20–26°C | < 18°C or > 28°C | ASHRAE 55 |
| Relative humidity | 40–60% | 30–70% | < 20% or > 80% | ASHRAE 55 |
| Ventilation rate (office) | ≥ 8.5 L/s/person | ≥ 5 L/s/person | < 3 L/s/person | ASHRAE 62.1 |
| Illuminance — open office | 500 lux (desk level) | 300–500 lux | < 200 lux | IES, EN 12464-1 |
| Background noise — office | NC 35–40 | NC 40–45 | > NC 50 | ASHRAE, WELL |
Impact on Health and Productivity
Research consistently shows that IEQ directly affects occupant performance:
- Harvard COGFX Study: Doubling ventilation rates improved cognitive function scores by 101%. CO₂ above 1,000 ppm reduced decision-making by 50%.
- Temperature: Productivity decreases by 2% for every °C above 25°C (Seppänen et al., 2006).
- Lighting: Daylight access improves sleep quality by 46 minutes/night and reduces absenteeism (Boubekri et al., 2014).
- PM2.5: 10 μg/m³ increase in PM2.5 associated with 1% cognitive performance decline.
IEQ Monitoring
Continuous monitoring is increasingly standard in quality commercial buildings:
- Essential sensors: CO₂, temperature, humidity — minimum requirement
- Enhanced sensors: PM2.5, PM10, TVOC, formaldehyde — required for WELL certification
- Monitoring platforms: Cloud-based dashboards displaying real-time IEQ data
- Cost: Basic CO₂/temp/humidity sensor: $100-300/unit. PM2.5 sensor: $200-500/unit. Full platform: $1-3/m²/year.
Bangladesh Context
- Outdoor air pollution: Dhaka PM2.5 frequently exceeds 100 μg/m³ — effective air filtration (MERV 13+) in AHUs is essential to achieve good indoor PM2.5.
- Ventilation challenges: Many buildings use minimal outdoor air to reduce cooling load — this saves energy but worsens IAQ.
- High humidity: 70-90% RH in monsoon. Without proper dehumidification, mould growth and comfort problems are common.
- Construction dust: Adjacent construction (frequent in Dhaka) creates PM10/PM2.5 spikes. Building pressurization and filtration are countermeasures.
- Temperature expectations: Many buildings overcool to 18-20°C, wasting energy. 24-26°C with good air movement is comfortable and efficient.
References
- ASHRAE 62.1 — Ventilation for Acceptable Indoor Air Quality
- ASHRAE 55 — Thermal Environmental Conditions for Human Occupancy
- WELL Building Standard v2 — Air, Thermal Comfort, Light, Sound concepts
- Harvard COGFX Study — Associations of Cognitive Function with Carbon Dioxide
- WHO — Global Air Quality Guidelines (2021)
Insights & Guidance
- IEQ has four dimensions: air quality, thermal comfort, lighting, and acoustics. All affect productivity.
- CO₂ above 1,000 ppm reduces decision-making by 50% (Harvard COGFX study). Target: ≤800 ppm.
- PM2.5 ≤15 μg/m³ indoors is the WELL threshold. In Dhaka (outdoor PM2.5 often >100), MERV 13+ filtration is essential.
- Temperature: 22-26°C is the comfortable range. Overcooling to 18°C wastes energy without improving comfort.
- Ventilation rate: ≥8.5 L/s/person for offices (ASHRAE 62.1). Many buildings in Bangladesh provide less.
- Continuous IEQ monitoring (CO₂, temp, humidity, PM2.5) is increasingly expected in quality commercial space.
Occupant health and productivity are directly tied to IEQ. Staff costs are typically 10-100x building operating costs — a 2% productivity improvement from better IEQ far outweighs the investment. For WELL and LEED certification, IEQ parameters must meet specific thresholds. MNC tenants increasingly require IEQ monitoring data. In Dhaka, where outdoor air pollution is severe, indoor filtration is a health necessity, not a luxury.
- Sick Building Syndrome — high CO₂, poor ventilation, and VOC off-gassing cause headaches, fatigue, respiratory issues.
- Mould growth — high humidity (common in Bangladesh monsoon) without dehumidification leads to mould, which causes respiratory illness and property damage.
- PM2.5 infiltration — without proper filtration, Dhaka's outdoor pollution becomes indoor pollution.
- Overcooling — 18°C set-points waste 30-40% cooling energy vs 24°C.
- Noise complaints — open-plan offices without acoustic treatment reduce concentration and satisfaction.
- IAQ monitoring data — CO₂, temperature, humidity (continuous or periodic)
- PM2.5 monitoring data (especially in Dhaka)
- Ventilation system commissioning report — outdoor air rates verified
- Filter replacement records — MERV rating, replacement schedule
- Thermal comfort survey results
- Lighting survey — lux measurements at workstations
- Stuffiness or odour — indicates poor ventilation.
- Condensation on windows or walls — indicates humidity problems.
- Visible mould — serious IAQ issue.
- Temperature: too cold (overcooling) or too warm?
- Lighting quality — dark corners, glare on screens, no daylight?
- Noise levels — can you concentrate? Is there excessive HVAC or traffic noise?
- Is indoor air quality monitored? What are the CO₂ and PM2.5 readings?
- What is the MERV rating of AHU filters? How often are they replaced?
- What is the temperature set-point? Can occupants adjust it?
- Is there a fresh air / ventilation system? What is the outdoor air rate?
- Has a lighting survey been conducted? What lux levels are achieved?
- IAQ assessment — certified industrial hygienist or IAQ consultant.
- Mould investigation — environmental hygienist for assessment and remediation.
- WELL certification — WELL AP for standard requirements and testing.
- Acoustic design — acoustic consultant for open-plan noise management.