Indoor Air Quality (IAQ)

Detailed Explanation

Indoor air quality (IAQ) is a multi-parameter concept measuring the impact of breathed air in an enclosed space on health, cognitive performance, comfort and productivity. Per WHO, ASHRAE, EPA and EU data, people spend 85-90% of their lives indoors; making IAQ far more critical than outdoor air quality.

IAQ assessment uses 6 main parameters:

1. Thermal comfort — temperature (T), relative humidity (RH), air velocity (v), surface temperature (Tr), clothing insulation (clo), activity level (met). Calculated via PMV-PPD indices (TS EN ISO 7730).

2. CO2 — by-product of human metabolism, indicator of inadequate ventilation. ASHRAE limit 1,000 ppm (quality target <800 ppm), cognitive performance drops 20% above 1,500 ppm (Harvard COGfx study).

3. Particulate matter (PM) — PM10 (≤10 μm, upper respiratory), PM2.5 (≤2.5 μm, alveolar penetration), PM1.0 (≤1.0 μm, enters bloodstream). WHO 24-h limit PM2.5 15 μg/m³, PM10 45 μg/m³.

4. VOCs (Volatile Organic Compounds) — from paint, furniture, carpet, cleaning products, photocopiers; formaldehyde, benzene, toluene etc. Total VOC (TVOC) <500 μg/m³ as quality target.

5. Microbiological load — bacteria, mould, virus, allergens. Legionella (water system), Aspergillus (HVAC scale), SARS-CoV-2 (inadequate ventilation).

6. Relative humidity — the hidden regulator of IAQ; below 30% RH respiratory drying, static; above 60% RH mould, mites, allergy risk. Optimum 40-60%.

These six parameters interact: high RH + low ventilation = mould; low RH + static = electronic damage + increased virus spread (SARS-CoV-2 stays viable 60% longer at low RH — China Public Health 2021).

Why It Matters

IAQ impact is measured across health, productivity, financial and regulatory dimensions:

1. Health impact — Sick Building Syndrome (SBS) symptoms (headache, eye irritation, mucosal dryness, fatigue) appear in 30-40% of indoor workers; especially in low humidity (25-35% RH), high CO2 (>1,000 ppm) + VOC combinations. WHO reports 20% of respiratory infections are IAQ-driven.

2. Cognitive performance — Harvard COGfx study (2015): office decision-making performance drops 50% as CO2 rises 600 → 1,400 ppm. At 30% RH mucosal dryness + virus spread + distraction; productivity drops 15-25% (Allen et al. 2019).

3. Financial impact — for a mid-sized 500-person office with average annual payroll of 25 M USD; a 5% productivity gain = 1.25 M USD/year. IAQ improvement investment is typically 100,000-300,000 USD; ROI <6 months.

4. Regulatory compliance — TS EN 16798-1 (2019) mandatory in EU buildings; ASHRAE Std 62.1 reference; LEED v4.1 + WELL Building Standard high-credit category. Turkish OHS regulation has required IAQ measurement since 2018.

5. Post-pandemic transformation — SARS-CoV-2 reset IAQ perception; ASHRAE Epidemic Task Force 2020 report recommended RH 40-60% + MERV-13 filtration. WELL Building IAQ category raises rental value by 3-7% (JLL 2022 research).

Indoor air quality is not just an HVAC capacity calculation but a system topic in which temperature, RH, CO₂, particulates and VOCs are treated together.

Practical Example

An 18,000 m² office tower built in 2019 in Levent, Istanbul. 1,200 staff, finance + consultancy tenants. Post-pandemic IAQ assessment in 2022.

Baseline assessment: • Temperature: 22-24°C ✓ ASHRAE • Relative humidity: winter 22-28%, summer 58-65% ✗ (winter <30%, summer >60%) • CO2: average 950 ppm, peak 1,400 ppm ✗ (>1,000 ppm sustained) • PM2.5: 18-25 μg/m³ ✗ (above WHO 15 μg/m³) • VOCs: TVOC 720 μg/m³ ✗ (above 500 μg/m³) • Complaint rate: 42% of staff with SBS symptoms

Occupancy data: lease occupancy 85%; real occupancy 62% (post hybrid work). 2 floors did not renew their leases (-2.4 M USD/year revenue loss).

IAQ improvement package:

1. Humidification — 8 × Neptronic SKE4-90 (90 kg/h) (720 kg/h total), winter 45% RH ± 5 guaranteed. RO water system, in-duct SAM-e distribution. Capex: 280,000 USD

2. Dehumidification — 4 × condensing dehumidifier units integrated into AHUs for summer, 50% RH ± 5 guaranteed. Capex: 95,000 USD

3. Filtration upgrade — F7 → MERV-13 + HEPA prefilter, PM2.5 < 10 μg/m³ target. Capex: 65,000 USD

4. CO2-sensor DCV — dynamic ventilation across 36 zones, OA modulation. Capex: 45,000 USD

5. NKT - Climate Track IAQ Pro — 48-point T/RH/CO2/PM/VOC monitoring, mobile dashboard, tenant reporting. Capex: 35,000 USD

Total capex: 520,000 USD. Financial result (12 months later): • Occupancy 62% → 88% (vacant floors re-leased) • Annual rent increase: 1,800,000 USD • ROI: 4 months • Staff complaint rate: 42% → 8% • WELL Building Gold certification

This example shows IAQ is not just a health concern but a financial-strategic tool.

Engineering Note

Engineering criteria in IAQ design and system optimisation:

• Multi-parameter approach — not only temperature and RH but CO2, PM, VOCs and microbiological load must be evaluated jointly. Single-parameter optimisation (e.g. cooling only) worsens other parameters. • Dew-point-based control — RH readings drift with temperature; dew point is more reliable. The psychrometric conversion is calculated directly from RH and temperature. • Seasonal optimisation — winter humidification + summer dehumidification + shoulder-season economizer + year-round ventilation; each season needs a different control strategy. • Ventilation vs filtration balance — high OA (ventilation) dilutes CO2 + VOCs but increases particulate ingress; MERV-13 + HEPA filtration must be combined with high OA. • Demand-Controlled Ventilation (DCV) — CO2-sensor-driven dynamic OA modulation, 25-40% energy savings + IAQ quality preservation; fixed OA wastes energy and overdries indoor air during low-occupancy hours. • Microbiological control — UV-C lamps integrated into HVAC inactivate moulds and viruses up to 99%; DI water + UV-C standard for Legionella control in water systems. • Condensation risk — high RH causes condensation + mould on cold surfaces (windows, exterior walls, chilled-water pipes); the control strategy must include surface-temperature monitoring + time-delayed RH adjustment. • Sensor placement and calibration — not the shop/office average but the occupant breathing zone (1.4-1.7 m height); 12-32-point multi-sensor network; calibration twice a year. • Reporting and transparency — tenant/occupant dashboard with daily IAQ report; used in WELL Building, LEED and ESG reporting.

NKT Application Link

For this application NKT – Nem Kontrol Teknolojileri supplies TFT, Neptronic and Microwell equipment. It supports unit selection with capacity calculation and technology matching based on space conditions, target temperature and RH (or dew point) and moisture load, and provides technical service and spare parts. Design, installation and commissioning remain within the scope of the facility's designer and contractor.