Definition
Special environments where airborne particle count, temperature, humidity, and pressure are controlled according to ISO 14644 standards. Used in pharmaceutical production, semiconductor fabrication, and medical device manufacturing. Humidity control is critical for both product quality and static electricity prevention.
Detailed Explanation
A cleanroom is a specialized engineering environment where airborne particle concentration, temperature, humidity, and pressure are controlled within defined limits. The primary reference standard is ISO 14644-1, which defines 9 cleanliness classes based on particle size and count (ISO 1 cleanest, ISO 9 least clean). The legacy FED-STD-209E "Class 100, 1,000, 10,000" classification is also still in use.
In pharmaceutical manufacturing, the EU GMP Annex 1 classification is used: • Grade A: aseptic filling, most critical (ISO 4.8 dynamic) • Grade B: A zone surroundings, preparation (ISO 5 dynamic) • Grade C: bulk preparation (ISO 7) • Grade D: packaging, storage (ISO 8)
The link between particle control and humidity: 1. Static electricity — low RH (<30%) causes dust to adhere to surfaces and products. Optimum RH 45–55%. 2. Microbial contamination — high RH (>65%) supports bacterial and mold growth. RH of 30–55% is recommended in Grade A/B zones. 3. Particle generation — low RH causes stress cracking in polymers/electronics; high RH creates condensation-related contamination. 4. Operator comfort — low RH causes dry skin, high RH causes fatigue; both increase production error risk.
Humidity control strategy: condensation-type dehumidifier + steam/ultrasonic humidification to maintain a 45 ± 5% RH band.
Design Standards
ISO 14644-1 Classes (particles/m³, ≥0.5 µm): ISO 1: 0 ISO 2: 4 ISO 3: 35 ISO 4: 352 ISO 5: 3,520 ISO 6: 35,200 ISO 7: 352,000 ISO 8: 3,520,000 ISO 9: 35,200,000
Typical HVAC parameters: • Class 5 (ISO 5): 240–480 ACH, 95% ULPA filter, 30–55% RH, 20–22°C • Class 7 (ISO 7): 30–60 ACH, 99.99% HEPA H13, 30–60% RH, 20–24°C • Class 8 (ISO 8): 10–20 ACH, recommended 99.95% HEPA H12, 30–65% RH
Pressurization: • +10 to +15 Pa relative to adjacent area • Maximum: +30 Pa (door force, usability limit) • Cascade: outdoor (0 Pa) → gowning (+5 Pa) → corridor (+10 Pa) → cleanroom (+15 Pa)
Filtration stages (general): F7 pre-filter → F9 intermediate filter → HEPA H13/H14 final filter
Practical Example
Class C (ISO 7) granulation room design at a pharmaceutical tablet facility:
Space: 80 m² × 3 m = 240 m³ Targets: ISO 7, 45 ± 5% RH, 21 ± 2°C, +15 Pa Process: moisture-sensitive maltoses; requires low RH (40%) Outdoor: summer 32°C, 65% RH; winter 0°C, 85% RH
Air circulation: 40 ACH × 240 = 9,600 m³/h Outdoor air: 15% (25 m³/h per person rule) → 1,440 m³/h
Summer moisture load: Outdoor air ingress: 1,440 × 1.2 × (19.3 − 8.1) g/kg = 19,354 g/h ≈ 19.4 kg/h Personnel (5 people): 5 × 80 = 400 g/h Process (granulator vacuum): 1,500 g/h Total: ~21.3 kg/h
Selection: a condensation-type dehumidification system integrated into the AHU (NKT CD1200-3000, model CD1500). The outlet air is 8°C, 95% RH (≈ 6.3 g/kg); reheat brings it to 21°C → room inlet W ≈ 6.3 g/kg → room maintains 40% RH.
In winter, outdoor air is low in humidity; oil-vapor or electric steam humidifiers maintain the 45% RH lower limit. Filtration: F7 + F9 + HEPA H13. Continuous particle monitoring (DOP test, periodic validation).
Engineering Note
Considerations in cleanroom HVAC design:
• Once-through vs recirculation — at high classes (ISO 5 and below), 100% outdoor air is nearly impossible (energy load); recirculation + supplementary outdoor air is standard. In pathogen-risk situations, 100% outdoor air may be mandatory. • Validation protocols — IQ/OQ/PQ (Installation/Operational/Performance Qualification) is mandatory in pharmaceuticals. NIST-traceable calibration of humidity sensors and periodic service of particle counters. • Humidifier hygiene — steam humidification is the only method accepted in GMP; ultrasonic or cold mist are not used in pharmaceutical Class A/B due to Legionella risk. • Reheat energy load — the condensation system cools air to 8°C, then reheats to 21°C. This reheat constitutes 25–35% of annual energy bills; energy recovery wheels or rotor integration provide energy savings. • Personnel density — the 25 m³/h per person outdoor air rule is sometimes insufficient. ASHRAE 62.1 and EU GMP Annex 1 tables should be consulted. • Surface materials — easy-to-clean, particle-free finishes (epoxy floor, steel panel walls) and hygienic junction design (radius corners, sealed silicone) are critical.
NKT cleanroom HVAC solutions (condensation-type + integrated dehumidification + filtration) are delivered to pharmaceutical, hospital, and electronics manufacturing facilities in compliance with GMP/ISO standards.
