Natural Ventilation

Detailed Explanation

Natural ventilation (infiltration) is the air exchange between a building interior and exterior without a mechanical device (fan, AHU, exhaust unit). This exchange occurs via three physical mechanisms:

1. Stack effect — warm interior air has lower density and flows out at high elevations, in at low elevations. Proportional to temperature difference (ΔT) and building height (h). 2. Wind effect — wind creates pressure differences across building façades; the windward face is at positive pressure (inflow), the leeward face at negative pressure (outflow). 3. Mechanical imbalance — exhaust fans inside the building (bathroom, kitchen, process extracts) create negative pressure that draws outdoor air in.

The unit of measure is ACH (Air Changes per Hour) or m³/h. Building envelope tightness is measured by blower door test (ACH50 value at 50 Pa pressure); practical infiltration is estimated as ACH50 / 17-20.

Per ASHRAE 62.1 and TS EN 16798 classification, typical ACH values: • Passive house (Passivhaus standard): 0.1-0.3 ACH • Modern tight building (LEED Gold+): 0.3-0.5 ACH • Standard office: 0.5-1.0 ACH • Older/leaky building: 1.0-2.0 ACH • Industrial workshop (door traffic): 2.0-5.0 ACH • Loading dock / warehouse (door continuously open): 5-15 ACH

Why It Matters

Natural ventilation is the hidden multiplier of humidification and dehumidification loads. Even without a mechanical makeup-air system, the building constantly breathes outdoor air. In winter, cold low-humidity outdoor air entering the space dries the interior; in summer, humid outdoor air increases moisture load.

Concrete example for a print shop: 5,000 m² × 6 m height = 30,000 m³ workshop, ACH = 1.2 (moderate leakage). Hourly infiltration = 36,000 m³/h.

Winter scenario (Ankara, -3°C / 75% RH outdoor, ≈ 2.4 g/kg absolute humidity): • Target: 22°C, 50% RH = 8.3 g/kg • Δw = 5.9 g/kg • Air mass: 36,000 × 1.2 = 43,200 kg/h • Humidification load: 43,200 × 5.9 / 1000 = 255 kg/h steam

If the same building were tight (ACH 0.4): 85 kg/h steam — one-third the capacity.

For this reason, building envelope tightening investment in new construction (door sealing, floor membrane, air curtains) can save 20-40% of humidification equipment capex. A pre-project blower door test is recommended; the real ACH value should come from measurement rather than estimate.

Practical Example

Consider a textile weaving workshop on the European side of Istanbul. 3,500 m² × 5 m height = 17,500 m³, production floor, continuous fabric and raw-material in/out flow, four 4×4 m loading doors (open ~20% of time at shift start).

ACH measurement: • Blower door test ACH50: 8.5 • Practical infiltration: 8.5 / 18 ≈ 0.47 ACH (steady, doors closed) • Door traffic effect: +1.8 ACH (at shift start, daily average) • Total average ACH: ~2.3 (during shifts, 8 h/day) • Off-shift ACH: 0.5 (night)

Cotton processing target: 22°C, 62% RH (for 8.5% regain). Winter peak (January, -2°C / 80% RH outdoor, ≈ 2.6 g/kg): • Target absolute humidity: 10.2 g/kg • Δw during shift: 7.6 g/kg, ACH 2.3 • Shift air mass: 17,500 × 2.3 × 1.2 = 48,300 kg/h • Shift humidification load: 48,300 × 7.6 / 1000 = 367 kg/h • Off-shift load: ~80 kg/h

Solution: 5 × Neptronic SKE4-90 (90 kg/h) units (450 kg/h total capacity), night-shift modulated control. Ambient conditions are monitored continuously; capacity is modulated to the shift pattern. Annual energy savings vs fixed-capacity operation: 35%.

Engineering Note

Engineering points for natural ventilation control and humidification/dehumidification load calculation:

• Blower door test standard — TS EN ISO 9972 (formerly EN 13829) test procedure; ACH50 measurement at 50 Pa, leakage mapping with thermal camera + smart smoke testing. • Stack effect is seasonal — winter ΔT of 25-30°C adds 0.3-0.5 ACH to infiltration in a 3-storey building; negligible in summer. • Wind effect — calculation from hourly meteorological data; typical correction factor 0.15-0.30. Higher in open areas, lower in cities. • Loading door operation — a single 4×4 m door open 20% of the time delivers 8,000-15,000 m³/h of infiltration alone; an air curtain reduces this load by 60-80%. • Seasonal ACH variability — summer vs winter stack-effect difference, outdoor-air usage profile (summer open windows) — control strategy must accommodate annual variation. • Infiltration vs ventilation — IAQ minimum requirement (ASHRAE 62.1 for offices: 2.5 L/s/person + 0.3 L/s/m², i.e. about 8-10 L/s/person at typical office occupancy) cannot be met by natural means; mechanical supply/exhaust is required. • CO2 measurement — proxy for actual ventilation rate; if CO2 >1,000 ppm, infiltration < required per-person supply.

NKT calculation methodology: real ACH measurement + hourly meteorological data + 4-season simulation = humidification/dehumidification capacity optimisation (preventing over/under sizing).

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.