The Ultimate Guide to Cleanroom HVAC Systems: From System Division to Design Essentials

As a vital component of cleanroom control systems, the HVAC (Heating, Ventilation, and Air Conditioning) system plays a crucial role in regulating and monitoring air temperature, humidity, airborne particles, and microorganisms in the production environment. Its main objective is to ensure environmental parameters meet quality standards, prevent air contamination and cross-contamination, and provide a comfortable environment for personnel. Additionally, the HVAC system minimizes and prevents adverse effects on workers during production and safeguards the surrounding environment. In cleanroom design, maintaining a clean and secure space is a fundamental consideration.

1. HVAC System Division

1. By Product Type: To prevent cross-contamination between products or due to different purification requirements.

2. By Cleanroom Classification or Temperature/Humidity Requirements: Cleanrooms with varying classifications (A, B vs. C, D) or environmental requirements should have separate systems.

3. By Filtration Level: Non-purified, medium-efficiency, and high-efficiency purification systems must be separated due to large differences in airflow resistance.

4. By Airflow Type: Unidirectional and non-unidirectional cleanrooms should be in separate systems to account for different air exchange rates and prevent excessive reheating.

5. By Floor, Area, or Process Section: Allows independent operation of production areas, supporting energy savings.

6. Special or Contaminated Areas: Independent systems should be designed for environments handling highly sensitizing drugs, contraceptives, vaccines, hormones, antineoplastic chemicals, highly toxic microbes, or areas with heavy dust generation.

7. By Production Cycle: Different systems for long-running vs. intermittent operations; storage areas should be separate from production zones.

2. Heat Sources for HVAC

1. Preferred Sources: Gas boilers, with urban steam supply as the top choice.

2. Energy Efficiency: Prefer hot water boilers. Use steam boilers if heating, humidification, or sterilization is required. Use gas and oil as backups for each other.

3. Boiler Room Standards: Classified as Class D buildings, with at least 7–10 m ceiling height. No rooms above the boiler. Independent buildings preferred; if inside the plant, use pressureless hot water or steam boilers ≤2 t/h.

4. Boiler Room Facilities: Must include a control room, lab (can be shared), water softening system, steam distribution tank, gas pressure regulating station, blowdown expansion tank, cooling pond, exhaust, trench, and equipment access doors.

5. Additional Requirements: Boiler makeup tank must be elevated; flue insulated; explosion vents and condensate drainage required; install flue economizers for energy efficiency.

6. Feed Pumps: Use multistage pumps with high pressure head; allow manual and frequency-controlled operation.

7. Layout Tips: Avoid placing equipment before/after boilers; place water treatment farther away in a separate room if possible.

8. Flue System: Ideally, each boiler should have an independent flue.

3. Cooling Sources

1. Water-Cooled Preferred: Better temperature control, ideal for constant temp/humidity systems.

2. Energy Flexibility: Consider steam lithium-bromide chillers if steam is available, with electric chillers as backup.

3. Centralized Cooling Plant: Should be located at the plant’s load center.

4. Design Considerations: Ceiling height of 6–9 m for easy pipe routing and maintenance; include trench, washbasin, control room, toilet, ventilation, etc.

5. Equipment Layout: Chill water units near windows for pipe extraction; large pumps horizontal, small ones in-line.

6. Pipe Structure: Large pipe diameters and loads require reinforced concrete beams or steel columns; hanging load ≥2–3 kN/m².

7. Pump Room Isolation: Lithium-bromide unit pumps should be in separate rooms to avoid overheating.

8. Cooling Capacity: Central units should be 15%–30% less than terminal demand.

9. Pipe Design: Use main pipes under beams; electric butterfly valves preferred for reduced resistance and easy control.

10. Cooling Tower Design: Overdesign slightly to delay the need for two units to run simultaneously. Discharge piping must slope downward without upward bends.

4. Terminal HVAC Equipment

1. Independent Air Handling Rooms: Required; if not possible, consider noise and maintenance issues.

2. Room Size: Preferably ≥9 m; include equipment access doors. First floor needs concrete foundation; upper floors require lightweight steel bases ≥150–200 mm.

3. Drainage: Provide floor drains and pipes for coil and humidifier sections.

4. Fresh Air Handling: Centralized processing is energy-efficient. Supply chilled water at 5–7°C; recirculation at 12–19°C. For strict humidity needs, use desiccant wheels.

5. Valve Placement: Avoid installing valves above AHUs or under ducts to prevent leaks.

6. Rain Louvers: Design larger than fresh air ducts to minimize water ingress.

7. Silencer Design: Install in supply, return, and exhaust main ducts. Use non-combustible materials. Cleanrooms: microperforated plates; HVAC: impedance composite; exhaust: duct-type.

8. Pressure Taps: Install in fresh, supply, and return ducts. Before/after filters for pressure monitoring. Required for fan testing and contaminant checks.

9. Valve Setup in Clean Systems: Use motorized shutoff and regulating valves; install insect screens at fresh air intakes. Use VAVs to maintain room pressure as needed.

10. Fresh Air Ducts: Wall inlets should follow modular sizing (e.g., 1200×600 mm). Duct and inlet sizes based on 60%–100% of design fresh air volume.

11. Return Ducts: 70%–90% of supply airflow → same size; 30%–70% → one size smaller.

12. HEPA Terminal Design: Airflow 60%–80% of rated capacity.

13. Fan Coil Selection: Account for load, function, and orientation. Example:

• Office: 170 W/m²

• Rooftop Office: 200 W/m²

• Meeting Room: 250 W/m²

• Rooftop Meeting Room: 300 W/m²
  Does not include fresh air load.

14. Fresh Air Volume: Minimum air exchange rate: 1.5–3 ACH.

15. Computer Rooms: Precision AC required. Cooling load ≥700 W/m². CO₂ system tightness must be considered.

16. Heat-Generating Areas: Require independent chilled water systems and 4-pipe systems with separate hot/cold coils.

17. Northern Areas: Frost, sand, and coal dust protection are essential.

18. Airflow Balance: Use valves on diffusers and branches. Avoid mixing ducts of different cleanliness levels, pressure, or temperature/humidity.

19. AHUs without Mechanical Rooms: Install in ceiling with soundproof casing and allow maintenance space.

20. Electric Heaters in AHUs: Use pressure-differential shut-off instead of airflow cut-off. Safety measures: grounding, overheat, and pressure alarm shut-off. Reheat sizing based on partial load.

21. Fresh Air Control: Use pressure-independent constant airflow valves on FCU branches.

22. Return Air Design: Second return optional; coil design should support both first and second return scenarios.

5. Air Ventilation System

1. Fan Redundancy: Critical systems must have backup fans.

2. One-to-One Exhaust: Critical equipment should have dedicated exhaust fans.

3. Heat Recovery: Use in direct-flow HVAC systems for energy savings.

4. Elevator Machine Rooms: Require ventilation (50 ACH) and split AC systems.

5. Toilet Exhaust: Preferably via built-in shafts.

6. Duct Material: Depends on exhaust type.

7. Duct Shape: Round for small ducts; rectangular for large ones.

8. Low-Noise Buildings: Use silenced fan boxes for labs and offices.

6. Pollution Control

Design must minimize air quality impacts on processes, equipment, and operations.

• Locate Pollution Sources: Identify locations, dimensions, type, and volume.

• Choose Exhaust Type: Use local, compartmentalized, or full-area exhaust systems.

• Best Practice: Isolate source in a negative-pressure compartment for optimal control