Wan-level Clean RoomISO Class 7 requires stringent controls over air cleanliness, temperature and humidity, and pressure differences, with its HVAC system (commonly referred to as the air purification HVAC system) being the core safeguard.
When selecting, it is crucial to consider the following key points:
One, Core feature requirements and parameters have been determined.
Cleanliness Grade (ISO Class 7):
Specific and Clear Particle Control Standards (such as) Particles ≥0.5μm: ≤352,000 particles/m³.
Ensure the efficiency and configuration of the end-of-line High Efficiency Particulate Air (HEPA) filters (typically H13 or H14), and confirm adequate air changes per hour (usually ≥40 cph, specific calculations required).
Key Selection Criteria: Calculate the total air delivery volume (considering the air change rate and room volume), and select an air conditioning unit and fan that can provide sufficient air volume and head to meet the system resistance.
2. Humidity and Temperature Control Accuracy:
Based on process requirements (such as electronics, pharmaceuticals, medical devices, precision manufacturing, etc.), determine precise temperature and humidity ranges (such as...). T=22±1℃, RH=45±5%）。
Selection Key:
Cooling/Heating Capacity: Precisely calculate cooling and heating loads, including envelope structures, personnel, equipment, lighting, fresh air, fan temperature rise, etc., and consider redundancy (such as N+1). Special attention must be given to the heat dissipation and humidity load of process equipment during load calculation.
Control Accuracy: Select systems equipped with high-precision, rapid-response temperature and humidity sensors and control valves (such as electric two-way valves, steam humidification valves). The design and sub-control strategy of the evaporative cooler/heat exchanger (such as regional control of chilled water flow) are crucial.
Dehumidification/Humidification Capacity: Determine the dehumidification amount based on the large moisture load (staff, fresh air, process), typically requiring deep dehumidification in the fresh air pretreatment section or a desiccant dehumidifier; and determine the humidification amount based on the small moisture load, usually using clean steam or electric heating/electric electrode humidification.
3. Differential Pressure Control:
Maintain positive pressure differentials between the cleanroom and adjacent lower-grade areas (typically ≥5Pa, with critical areas possibly requiring ≥10-15Pa).
Selection Key:
Airflow Balance: The system must have the capability to precisely adjust the air supply, return, and exhaust volumes (including process exhaust).
Variable Air Volume Control: Highly recommend using Variable Air Volume (VAV) systems, such as Pressure-Independent VAV Boxes or Fan Array Units (FFU) systems, to dynamically maintain stable pressure differences, particularly during door openings and when exhaust equipment starts or stops.
Pressure Relief Valve: An auxiliary protection measure has been implemented by installing backpressure valves in critical rooms.
4. New Airflow
Comply with personnel hygiene requirements (≥40 m³/h/person).
Increase local exhaust air volume to maintain the required air volume for positive pressure.
Compensate for air leakage volume.
Selection Key: Accurately calculate the required fresh air volume. Fresh air treatment is a major energy consumer, and its pretreatment (deep dehumidification, pre-cooling/pre-heating) and heat recovery solutions should be given priority consideration.
Two Key Selection Points for Air Handling Unit
1. Aircraft Type:Typically, a modular air handling unit (AHU) is selected, which should be a specialized type for cleanrooms (with smooth inner walls, resistant to dust accumulation, easy to clean, and good sealing).
2. Structural Material:The interior walls should be made of stainless steel (304 or 316L) or high-quality antibacterial galvanized steel plate (coated), with a robust frame. The insulation material must be a closed-cell material that is moisture-resistant and not prone to bacterial growth (such as rubber/PIR), and ensure good sealing.
3. Feature Segment Configuration:Please include and arrange the following content in order:
New section: Install pest-proof netting and air dampers.
Initial efficiency filter section: G4 or F5/F6, protecting subsequent components.
Pre-heating Section: Anti-freezing for Cold Areas (Hot Water Piping or Electric Preheating)
Mixed air/return air section: equipped with regulating valves.
Medium Efficiency Filtration Sections: F7/F8/F9, protecting the end high-efficiency filters and coils.
Cooling Section: Deep dehumidification and temperature reduction. Key Section! The number of tube rows and fin spacing must meet dehumidification requirements to avoid carrying water. Consider multi-stage control.
Additional Note: Compensation for overcooling after dehumidification, with precise temperature control (hot water coil or electric heating). Key Point!
Humidification Section: Clean steam or electric/elec-trode humidification (ensuring pure water quality, preventing scale and bacterial growth). Typically located after the fan and before the air distribution section.
Turbine Section: Key Segment! Select backward-inclined centrifugal fans (high efficiency, stable curve) with variable frequency drives (VFD). Adequate air volume and pressure head must be ensured (typically ≥15-20%, pressure head reserve is particularly important, considering the final resistance of the filter). Careful design is required for dual-fan configurations (supply/recirculate) or single supply with multiple returns.
Aerodynamic Section/Absorbing Section: Set after the fan to ensure uniformity of air delivery.
High-Efficiency Filtration Sections: F9 or H10/H11, serving as a pre-protection for the terminal HEPA filter (extending the lifespan of the HEPA).
Supply Air Section: Direct supply air ducts.
Chemical Filtration Section (excluding VOC/AMC), Heat Recovery Section (rotary, plate, heat pipe), Sterilization Section (UV lamps - use with caution regarding placement and intensity).
4Fan selection:
High efficiency, low noise.
Sufficient Wind Pressure: It is necessary to overcome the total resistance of initial, medium, and high-efficiency filters (initial + final resistance), surface coolers, heaters, piping systems, air valves, and terminal HEPA/FFU units, etc. The final resistance of the filter is the primary basis for selecting the pressure drop.
Variable Frequency Drive: Standard equipment for adjusting total air volume to maintain pressure difference and for energy-saving operation under partial load.
Sealability: Excellent sealing designs (such as EPDM sealing strips) must be implemented between different functional sections of the unit, doors, maintenance panels, etc., to ensure that the positive pressure section does not leak air and the negative pressure section does not吸入unfiltered air. Leakage tests must be conducted before shipment.
Drainage: Ensure a smooth and easy-to-clean drainage pan for the condenser section and humidifier section (if applicable), with sufficient slope, effective water seal in the U-bend, and a protective insect screen at the drain outlet.
Section 3: Airflow Organization and Terminal
1. Efficient Filter Arrangement:
Typically, a top-mounted HEPA (High-Efficiency Particulate Air) filter is used, combined with grated or perforated floor return air, to create a vertical unidirectional airflow (main clean zone) or non-unidirectional airflow (auxiliary areas).
FFU Systems: Another option, with high flexibility but slightly more complex control.
Key Selection Criteria: Determine the required number, size, and efficiency of HEPA/FFU units (H13 or H14). Ensure the installation frame is sealed reliably (liquid-tight seal or mechanical clamp seal), and perform a PAO/DOP leak detection scan after installation.
2. Return Air Method:Properly designed return air outlet locations and quantities ensure even airflow coverage, minimize dead spots, and effectively expel pollutants. Avoid short circuits.
