FFU Application and Equipment Selection Guide in Clean Rooms

The Fan Filter Unit (FFU) is also a necessary part of cleanrooms. Its distinctive structure can be easily connected in modular and is utilized in cleanrooms, clean benches, clean production lines, and prefabricated cleanrooms, as well as Class 100 cleanrooms. The FFU also uses an internal filter (primarily) and the high-efficiency filter. The air passes through a fan, is filtered, and is spread evenly with the speed of 45 m/s with a 20 percent deviation, which provides high levels of cleanliness in all environments. The FFU has many benefits compared with the traditional ductwork systems. It can be installed and maintained easily and enhances cleanliness and decreases noise and vibration during new construction or renovations of cleanrooms, saving much space and costs. Moreover, its flexibility, reusability, and negative pressure ventilation base its popularity as a layout of cleanrooms with a cleanliness rating of Class 1000 or higher. The FFU is also smaller in the air supply plenum than other systems, thus doing away with the necessity of more cleanroom space.

FFU Detailed Classification

• Case Dimensions: The chassis module dimensions can be determined and customized based on the centerline distance of the ceiling keels, as well as custom sizes.

• Case Materials: Available in standard coated steel, stainless steel, aluminum, and other materials.

• Motor Type: Available in AC and brushless DC. AC motors are further categorized as single-phase and three-phase.

• Control Methods: AC units offer control methods including single-mode and multi-mode step-down control, as well as stepless regulation such as voltage regulation or variable frequency control.

• Unit Static Pressure: Available in standard and high static pressure types.

• Filter Efficiency Classification: Based on their efficiency, high-efficiency filters can be categorized as high-efficiency filters and ultra-high-efficiency filters. A coarse pre-filter is also optional at the unit inlet.

The FFU system is mainly made up of four parts, namely the housing, deflector, fan, and control parts. The casing usually consists of galvanized aluminum alloy-coated steel, aluminum alloy, or stainless steel. It has the major role of assisting the fan and air guide ring and the deflector. The deflector, an airflow balancing device, is fitted to the housing, below and surrounding the fan. Single-phase AC, DC, and three-phase AC fans are available. In the case of AC FFUs, a five-speed speed regulator or stepless speed regulator is a popular control component. In the case of DC systems, the control chip is hardwired into the motor and can be remotely controlled by dedicated control software, a computer, a control gateway, and a network connection.

Basic FFU parameters and selection

General specifications for manufacturing equipment include：

• Dimensions: Must match ceiling dimensions.

• Material: Environmental requirements and cost factors must be considered.

• Surface velocity: Should be controlled within the 35-45 m/s range. Power consumption will vary depending on velocity.

• Static pressure: Must be sufficient to overcome wind resistance.

• Filter: Select based on Clean Room Classification.

• Motor: Consider power supply characteristics, power, and bearing life.

• Noise: Must meet cleanroom noise limits.

When selecting a model, consider the following basic parameters:

• Surface velocity: 0.35-0.55 m/s.

• Power consumption: AC systems typically range from 100-300 watts, while DC systems range from 50-220 watts. DC systems consume less power than AC systems.

• Air velocity uniformity: This refers to the uniformity of air velocity across the FFU surface. High-class cleanrooms require this, as failure to do so can easily cause turbulence. Excellent design and craftsmanship are crucial for this parameter. During testing, the surface velocity should be measured at 6-12 evenly selected points on the FFU outlet surface. The deviation between the maximum and minimum values and the average value must not exceed ±20%.

• External static pressure: Also known as residual pressure, this is closely related to the FFU's service life. Generally, the external static pressure is required to be no less than 90 Pa at a surface velocity of 0.45 m/s.

• Total static pressure: This refers to the static pressure the FFU can provide at maximum power and zero air velocity. AC FFUs typically have a static pressure of around 300 Pa, while DC FFUs have a static pressure of 500-800 Pa. At a given wind speed, the total static pressure can be calculated by adding the external static pressure to the filter pressure drop.

• Noise levels are typically between 42-56 dB. During operation, pay particular attention to noise levels at a face wind speed of 0.45 m/s and an external static pressure of 100 Pa. For FFUs of the same size, DC systems have a noise level 1-2 dB lower than AC systems.

• Vibration rate: Should be less than ?mm/s.

• Basic FFU dimensions include the basic module (i.e., the centerline distance from the ceiling keel), FFU enclosure dimensions, and filter dimensions.

Basic FFU Dimensions and High-Efficiency Non-Baffled Filter Selection

Selecting the right FFU is crucial in cleanroom design. Standard sizes include 575*575*285mm, 1175*575*285mm, 600*1200*285mm, and 1175*1175*360mm, allowing users to choose based on their specific needs. Choosing a high-efficiency non-baffled filter is also crucial, as its efficiency directly impacts the cleanroom's cleanliness. Common filter efficiencies on the market include H14 and U16. Users can select the appropriate filter based on their cleanroom class and requirements. FFU fans are available in both direct current (EC) and alternating current (AC) configurations. Our Amber uses Nidec motors from Japan, allowing users to balance their needs and budget.

FFU fan selection is crucial

Currently, there are two main types of fans on the market: DC fans (EC) and AC fans (AC). Each has its advantages and disadvantages, and users need to choose based on their specific needs and budget.
DC fans (EC) are suitable for cleanrooms with a large number of FFUs. They use computer software to intelligently control the operating status and fault conditions of each FFU, reducing maintenance costs. Furthermore, EC-FFUs can save over 30% energy compared to AC-FFUs, which can translate into significant annual energy savings for large FFU systems. EC-FFUs also feature low noise levels, further optimizing the cleanroom working environment. 

On the other hand, AC fans, while requiring less initial investment, may not offer the same control accuracy and energy savings as DC fans. AC-FFUs are typically equipped with manual speed regulators and are suitable for cleanrooms with fewer than 200 FFUs. However, as cleanroom size expands, the advantages of DC fans become more pronounced. Furthermore, filter configuration is important to consider when selecting a fan. Filter efficiency directly impacts the cleanliness of a cleanroom, so users need to select the appropriate filter based on the cleanroom's class and requirements. 

Furthermore, energy consumption varies between different FFU configurations, so users should prioritize configurations that minimize energy consumption while meeting cleanliness requirements.

Among FFU systems using the same fan type, systems using PTFE filters are more energy-efficient than those using glass fiber filters. For example, at a face velocity of 45 m/s, a DC FFU using glass fiber consumes 46 watts more power than one using PTFE, representing an 8% increase in energy consumption.

Common Problem Analysis

During testing, it is necessary to adjust the air volume, use sound-absorbing materials, and analyze whether there are specific areas of windmill noise variation. 

Installation difficulties may be caused by the following:

The FFU sizes are not the same as T-bar sizes, and the hook-shaped clips cannot be clamped due to 100% coverage. Maintenance issues are another typical issue, mostly because of insufficient clearance to change filters. 

Different factors are to be taken into account when choosing a motor. As an example, three-phase AC motors can be exposed to the threat of phase loss and burnout, whereas single-phase AC motors can be larger with the potential of causing imbalanced loads. DC motors also have relatively high building and maintenance prices but they are high efficiency. Thus, in practice, the right option has to be selected depending on the particular requirements and cost.
Moreover, one should not disregard harmonics. The main cause of harmonics is the non-fundamental voltages of frequency of the DC motor rectifier. This may result in high system current, failures in control systems and high temperatures and reduced service life of electrical components.
Terminal blocks and plugs are generally used as power connection options. Terminal block connections have long connection times, but they are commonplace accessories and can be used with smaller cleanrooms. Plug connections, in their turn, are easier and quicker, and are usually offered as an option, and are better to use in bigger cleanrooms. A choice of suitable connection method in practice should be determined on the size and requirement of the cleanroom.

• Filter Material: Whether a low-boron or boron-free filter is required, PTFE filters are a good choice for boron-free filters.

• Product Certification: Whether CE/UL/FM certification is required, both the motor and filter can be certified accordingly.