Is the fan box suitable for clean workshops? To be coordinated with filtration and differential pressure systems

The fan box can be used in clean factories, but it is not the decisive factor in cleanliness. The cleanliness level is guaranteed by filter efficiency, sealing method, air flow organization and operation management. The fan box is responsible for providing power to overcome the resistance of the filter section, air duct and end. Choosing the right fan box is only a part of the establishment of a clean system, but not the whole process.

Many projects tend to mix two things together when purchasing: the fan box is responsible for air supply power, and the filter is responsible for air cleanliness. If the division of labor between the two is unclear, problems will arise during model selection. For example, the fan box is selected based on ordinary ventilation conditions without considering the resistance of the high-efficiency filter at the end. After it is installed, the air volume is not enough, the number of air exchanges at the end is not reached, and the cleanliness naturally cannot be improved.

First look at its location in the clean air conditioning system

The air conditioning system of a clean factory usually consists of a fresh air treatment section, a circulating air treatment section, air supply pipelines, terminal filters and a return and exhaust system. The fan box may appear in several locations: as a circulating air unit, which returns the return air to the clean area after being filtered and coiled; as a fresh air unit, which processes outdoor fresh air before sending it into the system; as an exhaust unit, which discharges the clean area air outdoors or into the return air duct.

Different locations have different requirements for the fan box. The circulating air unit must overcome the resistance of the return air pipeline, filter section and air supply pipeline. The air volume is usually large and the pressure head is relatively low. The fresh air unit must overcome the resistance of the fresh air inlet, filter section and air mixing section, and also consider the impact of outdoor temperature changes on air density. The exhaust unit must handle air containing dust or chemicals, and the material and sealing requirements may be higher.

Where the fan box is placed in the system flow chart determines its air volume, static pressure, material and control method. If this issue is not clarified first, there will be no basis for selection.

Filter section resistance is the core variable in selection

The biggest difference between a clean system and an ordinary ventilation system is the resistance of the filter section. Ordinary ventilation systems may only have primary filtering and a resistance of tens of pascals. Cleaning systems usually have three stages of filtration: primary efficiency, medium efficiency, and high efficiency. The total resistance may reach hundreds or even thousands of pascals.

More importantly, filter resistance is not a fixed value. After the new filter is installed, it is the initial resistance. After running for a period of time, dust accumulates and the resistance gradually increases. When it needs to be replaced, it is the final resistance. The final resistance may be twice or more than the initial resistance. When selecting a fan box, the working point must be calculated based on the final resistance, not the initial resistance.

If you only select based on the initial resistance, the air volume of the fan box will be normal when it is first put into operation. After a few months of operation, the filter will accumulate dust, the resistance will rise, the fan working point will move in the direction of small air volume, the end air volume will decrease, and the cleanliness may not meet the standard. At this time, if the speed is increased to compensate, the motor load will increase and the energy consumption will increase. However, the amount of compensation depends on the fan curve and motor margin.

System end configurationWhen using HEPA/ULPA high-efficiency filters , the initial resistance of the filter and the resistance at the end of use should be included in the calculation of the working point. When the process requirements are higher, it can be evaluatedDoes the ULPA ultra-high efficiency filter meet the requirements? The filter replacement cycle and the pressure difference conditions during replacement should also be clarified during the selection stage.

The room pressure difference cannot only be determined by the air supply volume.

One of the core requirements of a clean factory is pressure differential control. A certain pressure difference needs to be maintained between areas with different cleanliness levels and between clean areas and non-clean areas to prevent pollution from spreading from low-level areas to high-level areas.

The pressure differential is determined by the supply air, return air, exhaust air and the room envelope. When the supply air volume is greater than the return air plus exhaust air volume, the room has a positive pressure; otherwise, the room has a negative pressure. The fan box provides air supply power, but whether the pressure difference reaches the standard depends on the opening of the return air valve, exhaust air volume, room sealing condition and door opening frequency.

In some projects, if the pressure difference fluctuates, the first reaction is to adjust the fan box speed. But if the return air valve is opened incorrectly, or the exhaust system is unstable, just adjusting the supply air volume will not solve the problem. Differential pressure control should be coordinated at the system level, and the speed regulation strategy of the fan box should match the actions of the differential pressure sensor and the return damper.

For multi-room clean systems, differential pressure control is more complex. Changes in pressure difference in one room will affect adjacent rooms, creating a chain reaction. The control strategy needs to consider the coupling relationship between each room, and each room cannot be adjusted independently. The sensor installation position, control response speed and valve action time will all affect the pressure difference stability.

Materials and maintenance should also be included in the design

The box material and surface treatment of the clean room depend on the installation area and air path. For fan boxes installed in clean areas, the surface of the box should be smooth, not prone to dust accumulation, and easy to clean. For fan boxes installed in non-clean areas but delivering clean air, the inner wall of the box should also be smooth to avoid the breeding of bacteria or particulate matter.

The method of maintenance is equally important. Filters need to be replaced regularly, and fans and motors need maintenance. If the fan box is installed in the suspended ceiling or mezzanine, the access door opening space, filter extraction direction and personnel operating position must be confirmed at the drawing stage. Just because the equipment can be placed in the computer room does not mean it can be maintained. The filter replacement path is blocked by the air duct, making subsequent maintenance difficult.

The exhaust system also needs to consider the medium characteristics. If the exhaust air contains dust, corrosive gases or high-temperature air, the box material, motor protection level and sealing method must be confirmed separately. Ordinary carbon steel boxes may rust quickly in corrosive environments, and ordinary motors may have poor heat dissipation in dusty environments.

Look at clean system selection from the perspective of complete machine matching

The core of the fan box selection for the clean system is to make the working point of the whole machine fall within the resistance change range of the filter section. From the initial resistance to the final resistance of the filter, the system resistance curve will move, and the fan operating point will change accordingly. When selecting, make sure that this change range covers the high efficiency area of ​​the fan, and that the motor and driver have margin to cope with the increase in resistance.

Aili Industry has independent supporting capabilities in fans, motors, controls and sheet metal structures. It can calibrate impellers, motors, drivers and boxes at the same working point. For clean systems, the working points can be calculated separately according to the initial resistance and final resistance of the filter section to confirm that the fan can meet the terminal air volume requirements throughout the entire operating cycle, rather than selecting based on an ideal state. This kind of internal coordination from the power end to the entire machine structure can reduce the common problems of insufficient estimation of filter section resistance and insufficient speed regulation range coverage in outsourced assembly solutions.

Clean room ceiling air supply is comparableFFU fan filter unit ; centralized management of multiple devices can be matchedThe FFU computer group control system realizes zone speed regulation and status monitoring. Protection of single process equipment can be consideredEquipment-side fan filter unit (EFU) . The final filtered air supply at the end of the air duct can beHigh-efficiency air supply outlet (HEPA BOX) . The division of labor boundaries between these equipment and the fan box should be clearly drawn on the system flow chart to avoid confusing power equipment and filtering equipment.

Specific structure and configuration options can be found inIt is confirmed in the fan box product catalog that non-standard projects should provide equipment or machine room drawings, and then finalize them based on the determined working points and on-site interfaces.