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Application of FFU in Clean Rooms and Equipment Selection Guide
2026/1/27
Compared with traditional duct systems, the FFU system demonstrates numerous advantages. It not only is easy to install and maintain, but also can enhance the cleanliness of newly built or renovated clean rooms, reduce noise and vibration, thereby significantly saving space and cost. Moreover, the flexibility, reusability, and negative pressure ventilation features of the FFU system make it the preferred layout method in clean rooms with a cleanliness level of 1000 or above.
Compared with other systems, the FFU system occupies less floor space within the air supply static pressure box and hardly occupies any space in the cleanroom.
Detailed classification of FFU:
◆ Classification by cabinet size: Based on the centerline distance of the ceiling truss, the modular dimensions of the cabinets are mainly divided into: 1200*600 (code 42), 1200*900 (code 43), 1200*1200 (code 44), 600*600 (code 22), 750*1500 (code 25), and non-standard sizes customized by customers.
◆ Classification of chassis materials: It includes standard coated steel plates, stainless steel plates, aluminum plates, and other materials.
◆ Motor classification: It is divided into AC motors and brushless DC motors. Among them, AC motors are further classified into single-phase and three-phase types.
◆ Classification of control methods: The control methods for AC power supply units include single-condition control, multi-condition step-by-step control, and continuous regulation such as voltage regulation or frequency conversion control.
◆ Classification of engine static pressure: It is divided into standard static pressure type and high static pressure type.
◆ Filter efficiency classification: Based on the efficiency of the high-efficiency filter, it can be divided into high-efficiency filters and ultra-high-efficiency filters. The inlet of the unit can also be equipped with a coarse pre-filter.
In addition, the FFU system is mainly composed of four parts: the box, the deflector plate, the fan, and the control components. The box material commonly used is galvanized aluminum alloy coated steel, aluminum alloy or stainless steel. Its main function is to support the fan and the air guide ring, as well as the deflector plate. The deflector plate is an air flow balancing device, located inside the box, around the bottom of the fan. The fan has three types of options: single-phase AC, DC, and three-phase AC. For AC FFU, the commonly used control components include a five-speed speed regulator or an infinitely variable speed regulator. For DC systems, the control chip is embedded inside the motor, and remote control is achieved through dedicated control software, computers, control gateways, and network lines.
The basic parameters and selection of the FFU, as well as the general specifications for the manufacturing of the equipment, include:
◆ Size: Must be compatible with the size of the ceiling;
◆ Material: Consider both environmental requirements and cost factors;
◆ Surface wind speed: It should be maintained within the range of 35 to 45 m/s. The power consumption will vary depending on the wind speed.
◆ Static pressure: Must be sufficient to overcome air resistance;
◆ Filter screen: Choose according to the cleanliness level;
◆ Motor: Consider the power supply characteristics, power capacity and bearing lifespan;
◆ Noise: It must comply with the noise limits set by the cleanroom.
When making the selection, the following basic parameters need to be taken into consideration:
◆ Wind speed: 0.35 - 0.55 meters per second.
◆ Power consumption: The power consumption of the AC system is usually between 100 and 300 watts, while that of the DC system is between 50 and 220 watts. The DC system consumes less power compared to the AC system.
◆ Uniformity of wind speed: This refers to the uniformity of the air velocity on the FFU surface. Higher-level cleanrooms have strict requirements for this aspect; otherwise, it may cause turbulence. Excellent design and craftsmanship are crucial for this parameter. During the test, 6 to 12 points should be evenly selected on the outlet surface of the FFU for surface wind speed measurement. The deviation between the maximum, minimum values and the average value should not exceed ±20%.
◆ External static pressure: Also known as residual pressure, it is closely related to the service life of the FFU. Generally, it is required that when the face air velocity is 0.45 m/s, the external static pressure should not be lower than 90 Pa.
◆ Total static pressure: This refers to the static pressure value that the FFU can provide when operating at maximum power and with zero wind speed. For AC FFUs, it is usually around 300 Pa, while for DC FFUs, it is between 500 and 800 Pa. At a certain wind speed, the total static pressure can be calculated by adding the external static pressure of the machine to the pressure loss of the filter.
◆ Noise: Typically ranges from 42 to 56 dBA. Pay special attention to the noise level when the face wind speed is 0.45 m/s and the external static pressure is 100 Pa. For FFUs of the same specification and size, the noise level of the direct current system is 1-2 decibels lower than that of the alternating current system.
◆ Vibration rate: Should be less than ? mm/s.
◆ The basic dimensions of the FFU: These include the basic module (i.e., the centerline distance of the ceiling truss), the size of the FFU cabinet, and the size of the filter, etc.
The basic dimensions of the FFU and the selection of high-efficiency filter without baffles
In the design of cleanrooms, the selection of FFU is of crucial importance. Its basic dimensions include both imperial units such as 1200×1200 and metric units such as 900×1200, allowing users to make choices based on their actual needs. At the same time, the selection of high-efficiency non-barrier filters is also a key step, as their efficiency directly affects the cleanliness of the cleanroom. Common filter efficiencies in the market include H14 and U16, and users can select the appropriate filter based on the cleanliness level and requirements of the cleanroom. Additionally, FFU fans have two options: DC fans (EC) and AC fans (AC), and users can make a trade-off based on actual needs and budget.
Selection of FFU Fans
In the design of a clean room, the selection of FFU fans is of great significance. Currently, there are mainly two types of fans available on the market: DC fans (EC) and AC fans (AC). These two types of fans have their own advantages and disadvantages, and users need to make a choice based on their actual needs and budget.
DC fan (EC) is suitable for cleanrooms with a large number of FFUs. It can intelligently control the operation status and faults of each FFU through computer software, thereby saving maintenance costs. Moreover, compared with AC-FFU, EC-FFU can save energy by over 30%, which is a considerable annual energy saving for large FFU systems. At the same time, EC-FFU also has the feature of low noise, further optimizing the working environment of the cleanroom.
On the other hand, although the AC ventilation fan (AC) requires less initial investment, it may fall short in terms of control accuracy and energy efficiency compared to the DC fan. AC-FFU is usually equipped with a manual speed regulator and is suitable for clean rooms with less than 200 FFUs. However, as the size of the clean room expands, the advantages of the DC fan will become more prominent.
In addition, when choosing the fan, the configuration of the filter also needs to be considered. The efficiency of the filter directly affects the cleanliness of the cleanroom. Therefore, users need to select the appropriate filter based on the level and requirements of the cleanroom. At the same time, the energy consumption of different configurations of FFU will also vary. Users need to choose the configuration scheme with lower energy consumption while meeting the cleanliness requirements.
In an FFU system using the same type of fan, the system using PTFE filter is more energy-efficient compared to the one using glass fiber filter. Taking a face wind speed of 45m/s as an example, the power consumption of the DC system FFU using glass fiber is 46w higher than that using PTFE, which means the energy consumption is 8% higher.
Analysis of Common Issues:
The noise problem often exceeds the expectations of the designers. During the testing process, it is necessary to adjust the air volume, use sound-absorbing materials, and analyze whether there are any special areas of noise variation from the wind turbine.
The installation difficulties may be caused by the following reasons: the size of the FFU does not match that of the T-Bar, or the 100% coverage area results in the inability to fix the hook-shaped retaining clips. Additionally, the inconvenience of maintenance is also a common issue, mainly manifested as a lack of sufficient operation space to replace the filters smoothly.
When choosing an electric motor, various factors need to be taken into consideration. For instance, three-phase AC power motor may have the risks of phase failure and burnout; while single-phase AC power motor may be larger in size and have unbalanced load. Although DC motor has high efficiency, its cost and maintenance expenses are also relatively higher. Therefore, in practical applications, an appropriate choice needs to be made based on specific requirements and budget.
Furthermore, the harmonic issue should not be overlooked. It is mainly caused by the rectification device of the DC motor, which generates voltages at frequencies other than the fundamental frequency. This may lead to increased system current values, control system failures, increased temperatures of electrical components, shortened service life, and other problems.
In terms of power connection methods, there are typically two options: terminal blocks and plugs. Terminal blocks take longer to connect but are usually standard accessories and are suitable for small clean rooms; while plugs are simpler and faster to connect and are usually optional accessories, more suitable for large clean rooms. In practical applications, the appropriate connection method needs to be selected based on the size and requirements of the clean room.
◆ Filter material: Do you need a low-boron or boron-free filter? The PTFE type filter is the option for boron-free filters.
◆ Product Certification: Are there any requirements for certifications such as CE/UL/FM? Both the motor and the filter can undergo relevant certifications.
