What needs to be considered when arranging the filter section before and after the fan?

When the filter section is placed in front of the fan, attention must be paid to the protection of the fan and subsequent components and the sealing of the negative pressure side; when placed in the back of the fan, attention must be paid to downstream pollution control, positive pressure sealing and air flow uniformity. The actual location should be determined based on the filtration level, wet and dry status, and system cleanliness goals.

Determine the layout value based on the objects to be protected

Inlet prefiltration is often used to reduce the entry of foreign particles into the processing chain. If downstream filtration is responsible for controlling particles that may be generated by upstream components, its relationship to the fan, coil and supply air connection should be checked. When the filter is close to the wet coil, the risk of water inclusion must also be assessed; when it is close to the fan outlet, it is necessary to check whether the airflow is concentrated on the local filter surface.

The pre-filtration function, negative pressure sealing and access door structure must be checked upstream of the fan; the air flow distribution, positive pressure sealing and downstream control tasks must be checked downstream of the fan; water droplets, moisture exposure and filter material application conditions must be checked in the adjacent wet section. The three types of positions correspond to different protection relationships and cannot be arranged just by the words 'filter section'. On what basis should the sequence of functional sections of the air conditioning box be determined? Please refer toOn what basis should the sequence of functional sections of the air conditioning box be determined?。

Characteristics of the filter section on the front side of the fan

When the filter section is located in front of the fan, the air is filtered before entering the fan, and the fan, downstream coil, humidification section and other components are less contaminated by particles. The front side is usually under negative pressure. If the box and access door are not tightly sealed, external unfiltered air may be sucked in and bypass the filter section. The seal inspection on the negative pressure side needs to focus on door seams, flanges and splices.

The filter section on the front side of the fan is also responsible for protecting downstream components. The filtration level and dust holding capacity need to match the inlet particle conditions. How to configure the primary and medium-efficiency filters in stages, please refer toHow to configure the primary-efficiency and medium-efficiency filters of air-conditioning boxes in different stages? . How to select the filter level according to the inlet air conditions, please refer toHow to select the air conditioning box filter grade based on the inlet air conditions?。

Characteristics of the filter section behind the fan

When the filter section is located behind the fan, the air is filtered after passing through the fan, and the filtered air directly enters the air supply pipe or end. The rear side is usually under positive pressure. If the seams of the box and the access door are not tightly sealed, the treated air may leak to the outside, but the outside air is not easily inhaled. The focus of sealing on the positive pressure side is to prevent untreated air from bypassing from upstream to downstream, and to prevent leakage loss of treated air.

The filter section on the rear side of the fan is closer to the air supply end, which is beneficial to downstream particle control, but the filter resistance will be included in the system resistance after the fan outlet. When the filter section is arranged behind the fan, the airflow uniformity may be affected by the fan outlet jet, and the wind speed distribution on the filter surface needs to be checked. For the influence of wind speed facing the coil, please refer toWhat impact does the coil head-on wind speed have on heat exchange and water entrainment in the air conditioning box?。

Additional checks should be made near wet coils and humidification sections.

When the filter is close to a wet coil, the water droplets behind the coil may make the filter damp, affecting the resistance and filter material condition. When the filter is close to the humidification section, insufficiently absorbed water mist may enter the filter material. Sufficient distance should be kept between the filter section and the wet section or water blocking measures should be installed, and the filter material itself should be checked to see if it allows a humid environment.

How to combine the slope of the water pan of the air-conditioning box with the layout of the drain outlet, please refer toHow to combine the slope of the water pan of the air-conditioning box with the layout of the drain outlet? . How to judge whether the MAU chemical filtration section is arranged before or after the surface cooler, please refer toHow to judge whether the MAU chemical filtration section is arranged before or after the surface cooler?。

Changes in location require rechecking the maintenance method

After the front and rear positions are adjusted, the filter extraction direction, pressure difference point and replacement space may all change. The wind direction and installation side should be drawn in the technical drawing, and the sealing method of the filter frame and installation frame should be confirmed. You cannot just move the 'filter section' back and forth in the functional section list while retaining the original inspection and measurement layout.

When the horizontal air-conditioning box is arranged against the wall, which side should be left for inspection? Please refer toWhen a horizontal air-conditioning box is arranged against a wall, which side should be left for inspection? . What functional segments should be included in the internal resistance of the air conditioning box? Please refer toWhat functional segments should be included in the internal resistance of the air conditioning box? . How to establish the fan pressure budget, please refer toHow is the total pressure of the air conditioning box fan determined by the internal resistance and external demand?。

Aili industrial supporting equipment

Aili Industrial can confirm that the filter and installation frame are matched with the box structure. When submitting the request, please indicate the filtration tasks and replacement channels at the same time. Aili Industrial has air filter manufacturing capabilities and can jointly confirm the filter size, grade, headwind speed, initial resistance and installation method with the air-conditioning box structure; the manufacturing end covers independent research and development and production of motors and fans, control systems, sheet metal, air filters and complete machine assembly. The interfaces and seals of the filter section and the fan section can be aligned in the same set; non-standard boxes can be adjusted according to on-site maintenance and air flow conditions.

Product form can be viewedAir handling unit andFan box page; terminal particle filtration can be combinedHEPA/ULPA filter confirmation; clean air supply package can be combinedFFU fan filter unit andCheck the fan filter unit at the EFU equipment end ; when it comes to gaseous pollution control, you can communicate separatelyChemical filter solutions. The specific layout, filtering effect and delivery scope still need to be verified based on the corresponding configuration data and on-site working conditions. Actual results are subject to on-site leak detection and particle test results.

Submit project parameters:https://ailigy.com/contactus.html

Related questions and answers

Is it better to place the filter section before or after the fan?
There is no single answer. It depends on the protection object, filtration level, wet section location and maintenance conditions. There are sealing and airflow issues that need to be checked before and after.

The filter section is on the front side of the fan, why should we pay attention to negative pressure suction?
The front side of the fan is usually under negative pressure. If the box or access door is not tightly sealed, external unfiltered air may be sucked in and bypass the filter section.

Can Aili Industrial help determine the location of the filter section?
The front and rear layout and sealing methods can be checked based on the filtration tasks, box structure and maintenance requirements. The specific plan needs to be confirmed according to the project conditions.

Related articles

1. On what basis should the sequence of functional sections of the air conditioning box be determined?

2. How to configure the primary-efficiency and medium-efficiency filters of air-conditioning boxes in different stages?

3. Should the high-efficiency filter of the air-conditioning box be placed inside the machine or at the end of the air supply?

4. What functional segments should be included in the internal resistance of the air conditioning box?

Key points for selection and acceptance inspection