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 outdoor, 3.2 g/kg absolute humidity): • Target: 22°C, 50% RH = 8.3 g/kg • Δw = 5.1 g/kg • Air mass: 36,000 × 1.2 = 43,200 kg/h • Humidification load: 43,200 × 5.1 / 1000 = 220 kg/h steam

If the same building were tight (ACH 0.4): 73 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. NKT engineering recommends a pre-project blower door test; 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 outdoor, 3.4 g/kg): • Target absolute humidity: 10.4 g/kg • Δw during shift: 7.0 g/kg, ACH 2.3 • Shift air mass: 17,500 × 2.3 × 1.2 = 48,300 kg/h • Shift humidification load: 48,300 × 7.0 / 1000 = 338 kg/h • Off-shift load: ~80 kg/h

Solution: 5 × Neptronic SKE4 80 kg/h units (400 kg/h total capacity), night-shift modulated control. NKT - Climate Track tracks ambient ACH variation in real time and tunes capacity to shift count. 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 (typically 8-12 L/s/person per ASHRAE 62.1) 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

NKT delivers season-adaptive humidification and dehumidification solutions for large industrial workshops (textile, printing, press, automotive assembly, raw-material storage) where natural ventilation load dominates:

1. Blower-door-based ACH measurement — pre-project test at 4 points, leakage map, real ACH value as design input. 2. Multi-unit capacity modulation — Neptronic SKE4 + SKG4 hybrid, shift/outdoor-air-based PID, 20-100% capacity band. 3. NKT - Climate Track ambient tracking — 16-32 point T/RH/dewpoint, derived infiltration calculation, real-time ACH value. 4. Air-curtain integration recommendation — engineering report for large loading doors, ROI typically 8-14 months. 5. CFD-supported air distribution — heat and moisture distribution simulation in large-volume workshops, sensor placement optimisation.

Sample typical project: 10,000 m² textile workshop, ACH 2.8 (shift), 8 × SKE4 80 kg/h, NKT - Climate Track 24 points, air-curtain integration. Annual moisture-load balancing: peak winter 580 kg/h, peak summer 220 kg/h, annual energy 1.1 GWh. 42% energy savings vs a fixed-capacity unit.