FFUs are self-powered units that operate independently of the central air conditioning system's supply pressure, handling the entire process of air intake, filtration, and clean air delivery. Their operating principle is as follows: the fan draws air in from the top of the unit; the air passes through two stages of filtration—pre-filtration and high-efficiency filtration—before being discharged across the entire outlet surface at a uniform velocity (typically 0.45 m/s ± 20%). This design ensures a very high level of air cleanliness and establishes a stable, unidirectional laminar airflow at the outlet, effectively preventing secondary contamination caused by air mixing.
Core Components and Operating Principles
FFUs typically consist of the following key components:
Housing: Acts as the structural framework; usually made of materials such as Al-Zn coated steel, stainless steel, or powder-coated cold-rolled steel, offering a combination of lightweight durability and corrosion resistance.
Fan: The core power component; typically a direct-drive centrifugal fan featuring a long service life (over 50,000 hours), low noise, maintenance-free operation, and stepless speed control.
Filter System: The core purification component; includes High-Efficiency Particulate Air (HEPA) filters (≥99.97% efficiency for 0.3μm particles) or Ultra-Low Particulate Air (ULPA) filters (≥99.9995% efficiency for 0.12μm particles). Some models feature a pre-filter (primary filter) at the fan intake to protect the fan and extend the lifespan of the main filter.
Air Deflector and Flow Equalizer: Located beneath the fan; utilizes a specialized airflow channel design to ensure uniform and stable discharge velocity, keeping deviations within ±20%.
Control Unit: Regulates fan speed and monitors operating status. Control methods range from simple multi-step switches and stepless speed controllers to advanced PLC or computer-based remote centralized control systems.
Key Parameters and Selection Criteria
When selecting an FFU, the following technical parameters should be prioritized:
Filter Efficiency and Cleanliness Class: These are the core indicators determining the FFU's purification capability. ULPA filters are mandatory for high-requirement areas classified as ISO Class 5 (Class 100) or cleaner (e.g., chip lithography, aseptic filling), whereas HEPA filters suffice for ISO Class 6–7 (Class 1,000 to Class 10,000) areas. FFUs can meet cleanliness requirements ranging from ISO Class 3 (Class 1) to ISO Class 9 (Class 1,000,000).
Face velocity and airflow volume: The standard face velocity is typically set at 0.45 m/s ± 20%. Airflow volume is calculated based on the cleanroom volume and the required air change rate (ACH). ISO Class 5 cleanrooms require ≥200 air changes per hour, while ISO Class 6 cleanrooms require 50–100 air changes per hour.
Noise: Cleanroom projects impose strict noise limits. Noise levels should not exceed 60 dB for non-unidirectional flow cleanrooms and 65 dB for unidirectional flow cleanrooms. High-quality FFUs can maintain noise levels between 45 and 55 dB(A) at a face velocity of 0.45 m/s.
Power consumption and fan type: EC (Electronically Commutated) DC fans are the mainstream choice today; they offer 30%–40% greater energy efficiency than traditional AC fans and support variable speed control. Power consumption typically ranges from 50 W to 300 W, depending on the specific model and airflow volume.
External static pressure (residual pressure): This indicates the FFU's ability to overcome resistance from the filter and supply air ductwork. At a face velocity of 0.45 m/s, the external static pressure is generally at least 90 Pa, with some DC FFUs capable of exceeding 200 Pa.
Réseau IPv6 pris en charge
