FFU vs. AHU in Cleanroom Selection

I. Understanding the Core: Basic Definitions of FFU and AHU

FFU (Fan Filter Unit): A modular air supply unit integrating a fan, high-efficiency filter (HEPA/ULPA), and diffuser plate. It is typically embedded within the plenum box above the cleanroom ceiling. Common single-unit sizes are 1200×600mm or 600×600mm. It allows independent control of start/stop functions and wind speed. Its core function is circulation filtration and terminal air supply to ensure high local cleanliness.

AHU (Air Handling Unit): A centralized air treatment equipment integrating functions such as filtration, cooling coils, heating, humidification, and fans. It requires a supporting duct system to deliver treated air to the terminal air supply outlets in the cleanroom. Its core function is centralized processing of fresh air + return air to uniformly regulate temperature, humidity, and cleanliness, making it suitable for large-area, lower-grade clean zones.

II. Core Differences: Comparison Across 7 Key Dimensions

• Cleanliness Assurance Capability

FFU: Equipped with HEPA/ULPA filters at the terminal end (filtration efficiency ≥99.99% @0.3μm), it can achieve vertical laminar flow with face wind speed uniformity ≤±15%. With a coverage rate of 80%-100%, it stably supports ISO Class 4-5 (Class 100 - Class 1,000) high-cleanliness zones. Particle settling efficiency is 5 times higher than AHU turbulent flow.

AHU: Typically uses standard high-efficiency outlets at the terminal end with face wind speed uniformity ≤±30%. Restricted by duct layout, its coverage rate is ≤60%. It is only suitable for ISO Class 7-8 (Class 10,000 - Class 100,000) clean zones. In high-grade scenarios, uneven cleanliness and localized particle exceedances easily occur.

• Energy Consumption Performance (Based on a 100㎡ ISO Class 6 Cleanroom)

FFU System: Single EC fan power ranges from 110-190W, with total power around 4.86kW. Air change rate is 50-60 times/h. Fan heat generation is 20-30W/unit, which must be factored into the cooling load.

AHU System: Includes MAU + AHU, with a total pressure loss of 1300Pa and total power around 17.2kW, which is 2.5 times higher than FFU. Summer dehumidification requires cooling below 5℃ before reheating, resulting in an energy waste of over 35%.

• Space Occupation and Ceiling Height Requirements

FFU: Requires a 0.6-0.8m plenum box inside the suspended ceiling, resulting in a net height loss of ≥300mm, but no dedicated machine room is needed. For example, a chip packaging and testing plant (ceiling height 4.8m) using the FFU solution achieved a 3.2m net height, which was 0.6m higher than the AHU solution.

AHU: Requires an independent machine room (area ≥20㎡). Large supply and return air ducts are laid within the suspended ceiling, occupying 35% of the space. Net height loss is significant, and renovation projects are often restricted by limited ceiling heights.

• Renovation Flexibility

FFU: Modular design allows for individual addition/removal of units and zonal control. Renovations do not require altering ductwork, resulting in shorter construction periods and less downtime. Upgrading cleanliness simply requires adding more FFUs, taking only 1-2 days for a single zone.

AHU: Ductwork is fixed. Renovation requires redesigning the duct layout and adjusting unit parameters, leading to complex construction and long timelines. Upgrading cleanliness essentially equates to rebuilding, involving high costs and extended shutdown cycles.

• Temperature and Humidity Control Precision

FFU (paired with MAU + DCC): Decoupled temperature and humidity control. DCC dry cooling coils respond in <30 seconds with temperature fluctuations ≤±0.3℃. MAU utilizes two-stage cooling coils + desiccant wheel dehumidification for dew point control precision of ±0.5℃, adapting to stringent scenarios like photolithography and precision manufacturing.

AHU: Single-stage cooling coil processing with coupled temperature and humidity control. Temperature fluctuation is ±1-2℃, and humidity fluctuation is ±3-5% RH, unable to meet high-precision process requirements.

• Maintenance Costs and Difficulty

FFU: Filter replacement cycle is 2-3 years; in-place scanning leak detection can be performed without shutting down. Lightweight (20-30kg per unit), requiring only one person for replacement. Annual maintenance costs are approximately 40% of those for AHU.

AHU: Filter replacement cycle is 1-1.5 years, requiring system shutdown and duct dismantling with multi-person collaboration. Ducts easily accumulate dust and leak, necessitating comprehensive cleaning and leak detection annually, leading to high maintenance costs.

• Initial Investment Cost

FFU: High unit procurement cost; complex construction for plenum boxes and suspended ceilings. Initial investment is 15%-25% higher than AHU.

AHU: Lower procurement costs for units and ductwork; mature construction processes; low initial investment. Suitable for projects with limited budgets and lower-grade clean zones.

III. Applicable Scenarios: Precise Matching to Avoid Mismatches

• Scenarios Prioritizing FFU

High-Grade Clean Zones: Semiconductor wafer manufacturing, advanced packaging, Micro LED exposure areas (ISO Class 4-5).

High-Precision Processes: Photolithography, precision instrument assembly, lithium battery electrode sheet manufacturing (temperature/humidity precision ±0.5℃, ±2% RH).

Height-Restricted / Renovation Projects: Old factory upgrades, projects requiring net heights ≥3m.

Multi-Zone / Flexible Production: Fast product line iterations requiring frequent adjustments to clean zones.

High Heat Load Workshops: IGBT testing areas, workshops with high-heat-generating equipment (heat generation ≥500W/㎡).

• Scenarios Prioritizing AHU

Low-Grade Large-Area Clean Zones: Food processing, ordinary pharmaceutical packaging, daily chemical production (ISO Class 7-8, area ≥1000㎡).

Budget-Constrained Projects: Strict initial investment controls, ordinary cleanrooms without high cleanliness demands.

Sufficient Ceiling Height & Fixed Processes: Factory ceiling heights ≥6m, long-term unchanged production processes.

Loose Humidity Requirements: Non-sterile pharmaceutical warehousing, ordinary electronic assembly (humidity ±5% RH or greater).

• Hybrid Solution (FFU + AHU) Applicable Scenarios

Composite scenarios where the core area requires high cleanliness while peripheral areas require lower cleanliness (e.g., semiconductor packaging workshops: core area ISO Class 5, peripheral area ISO Class 8).

Division of Labor: AHU handles fresh air + controls peripheral temperature/humidity; FFU ensures core area cleanliness.

Advantages: Balances cost and performance. Ensures core area compliance while controlling peripheral costs. This is currently the mainstream solution for mid-to-high-end cleanrooms.

Suzhou Pharma Machinery Co.,Ltd.

2026/06/16

Gino