I. Appearance of FFU
At present, all FFUs produced by various manufacturers can be distinguished by their appearance as follows:
1. From the shape perspective, there are two types: one is a rectangular shape, and the other has a sloping top. The sloping top of the FFU achieves a flow guiding effect, facilitating the flow and even distribution of air. The rectangular FFU usually relies on other paths to balance the air flow.
2. From the construction perspective, there are two types: one is an integrated type, and the other is a split type.
The advantages of the split type FFU are as follows:
① Facilitates the replacement of the filter
② Reduces the labor intensity during the equipment operation
③ Does not cause leakage

II. Components of FFU
At present, the most common components of various FFUs (in the order from top to bottom and from inside to outside) are as follows, depending on the different manufacturers and application environments, the components may be reduced.
1. Primary filter
Mainly to avoid damage to the high-efficiency filter caused by construction, maintenance or other unexpected situations, it serves to protect the high-efficiency filter and extend its service life.
2. Shell
The materials are mainly steel plates, aluminum plates, aluminum alloys, hard plastics, stainless steel, etc. Different manufacturers and different application environments have different choices, with a thickness of approximately 1.2 to 2.0, depending on the thickness, some can accommodate people.
3. Air duct connection components
In occasions with a lower cleanliness level (≤1000 grade, Federal Standard 209E), at the top of the ceiling there is no static pressure box at present. The FFU with air duct connection components makes the connection between the air duct and the FFU very convenient.
4. Motor
Currently, both AC motors and DC motors are used in FFUs. DC motors have a large volume, high cost, and are easy to control, but have higher energy consumption. AC motors have a small volume, low cost, and require corresponding skills for control, and have lower energy consumption. The service life of the motors currently used in FFUs is approximately 4 to 100,000 hours. Some excellent motors have corresponding technologies, such as oil-free lubrication, sealed bearings, overheating protection, and significantly improved commutator service life.
5. Impeller
There are two types of impellers: forward inclination and backward inclination. Forward inclination is conducive to increasing the directional flow of the air flow and enhancing the ability to remove dust. Backward inclination is conducive to reducing energy consumption and reducing noise.
6. Air flow balancing equipment
With the continuous spread of FFUs, most manufacturers have begun to install air flow balancing equipment to adjust the air flow of FFUs and improve the air flow distribution in the cleanroom. Currently, this balancing equipment is approximately divided into three types: one is a orifice plate, mainly adjusting the air flow of FFUs through the distribution of holes on the plate. One is a grille, mainly adjusting the air flow of FFUs through the density of the grille. The other is a power curve, mainly inducing the flow of air through the shape of the curve, and also adjusting the air flow through the distribution of holes on the curve.
7. High-efficiency filter
Mainly used to capture particles smaller than 0.5 microns and various suspended substances. The filter material is made of ultra-fine glass fiber paper, and the cutting board is made of coated paper, aluminum film, etc., and is bonded with wood frames and aluminum alloys. Each is tested by the flame test, having high filtration efficiency, low resistance, and large dust holding capacity. High-efficiency air filters can be widely used in air conditioning end supply locations of cleanroom workshops in industries such as optical electronics, LCD liquid crystal production, biomedicine, precision instruments, beverages and food, PCB printing, etc. High-efficiency and ultra-high efficiency filters are used at the end of the cleanroom, and their structural types can be divided into: with partitions, without partitions, large air volume, ultra-high efficiency, etc.
There are also three other high-efficiency filters, one is an ultra-high efficiency filter, which can achieve a purification rate of 99.9995%. One type is an antibacterial non-separation high-efficiency air filter, which has antibacterial effects and prevents bacteria from entering the clean workshop. The other is a sub-high efficiency filter, which is inexpensive and was previously widely used in purification spaces with low demand.
8. Metal Guard Screen
The primary function of the metal guard screen is to protect the filter. Most of them are anti-static.
9. Knife Edge
When FFU is used in some special occasions, the FFU with a knife edge can use a liquid tank for sealing, thus meeting the requirements of high sealing performance.
10. Control Unit
The control of FFU can be roughly divided into several types such as multi-level switches, continuous adjustment, and computer control, and the functions achieved include single-unit control, zone control, alarm, and operation status display.
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