Should the chemical filter air volume be selected based on the total air volume of the system or the air volume of a single unit?

This problem occurs very frequently in actual projects. You may encounter this problem when modifying air-conditioning boxes, adding chemical filtration sections to fresh air units, or installing circulating filtration at the equipment end.

The key is to figure out how the air passes through the filter section. Does the entire air flow pass through one section of the filter, or is it divided into multiple modules and connected in parallel? Is it series or parallel? These structures determine what caliber and air volume should be selected. If you choose the wrong caliber, either the filter is not enough, or you choose too large a filter, resulting in waste.

First determine how the air passes through

Before selecting a model, first understand the system structure.

tandem structure. If the filter section is connected in series on the air path, all system air volume will pass through this section of filter. In this case, the selected air volume is the actual air volume passing through the filter section, which is basically the same as the total air volume of the system.

Parallel structure. If multiple filter modules are installed in parallel, the total air volume will be distributed to each module. The actual air volume carried by each module depends on the branch resistance and flow distribution. When selecting, confirm the processing air volume of a single module instead of directly dividing the total air volume by the number of modules.

Series plus parallel combination. Some systems have both series-connected filter sections and parallel-connected module groups. In this case, it is necessary to confirm in sections: what is the air volume of each section of the filter, and how much does each module bear? For specific configuration, please refer to Discussion of the common product forms of chemical filters .

The same air volume is passed in series, and the processing volume is not added. In the series structure, each stage of the filter passes the same air volume, and there is no 'addition' argument.

Parallel modules share the air volume, but pay attention to the uniformity of distribution. When connected in parallel, the air volume distribution of each module depends on the branch resistance. If the air duct design is asymmetrical or the resistance of a certain branch is too high, uneven distribution of air volume may result. For specific balancing methods, please refer to whether the air volume balance needs to be re-done when modifying the chemical filter . Discuss

Check rated conditions

The air volume data on the sample needs to be compared with the actual working conditions.

The sample air volume should correspond to the size, medium and pressure loss conditions. The same type of filter may have different rated air volumes with different media filling amounts and different structural forms. When selecting, confirm what configuration the sample data corresponds to.

The target total air volume divided by the number of modules is only a preliminary estimate. This algorithm assumes that the air volume of each module is completely uniform, but this is not necessarily the case in reality. The impact of factors such as frame layout, air inlet distribution, maintenance status, etc. on distribution should also be considered.

The wind speed through which the filter material passes is also limited. If the air volume is too high and the contact time between the gas and the medium is insufficient, the treatment effect may be reduced. The air volume is too low and the processing capacity is not enough. When selecting, check whether the passing wind speed under the target gas, concentration and air volume is within a reasonable range. For specific calculation methods, please refer to Discussion on how to calculate the removal efficiency of chemical filters .

Temperature and humidity will also affect air volume. In high temperature or high humidity environments, changes in gas density and viscosity may affect the air volume passing through the filter section. If the working conditions are special, these should be considered when selecting.

Precautions for parallel connection of multiple modules

Parallel structure is relatively common in actual projects, and there are several points that need to be paid attention to.

Difference in branch resistance. The length of the branches connected to each module, the number of elbows, and the position of the air valve may be different. Different resistances will lead to uneven distribution of air volume. When designing, try to make the resistance of each branch as close as possible, or reserve adjustment means.

Inlet air distribution. If multiple modules are installed in a large frame, the location of the air inlets will affect the airflow distribution. The air volume of modules close to the air inlet may be larger, and the air volume of modules farther away from the air inlet may be smaller.

Maintenance status. If a module's filter material has been consumed or clogged, its resistance will change, possibly causing the air volume to be redistributed. When replacing filter media, pay attention to the impact on other modules.

Verification of single module air volume. After installation, it is recommended to measure the actual air volume module by module to confirm whether it is consistent with the design distribution. If the deviation is large, the damper needs to be adjusted or the structure inspected. Device-side applications such as For systems equipped with FFU chemical filters , the module’s air volume distribution and unit control methods also need to be checked together.

Verify actual operating point

After the design selection is completed, the actual operating point still needs to be verified.

After installation, measure the air volume of the system and each branch. Meeting the standard for total air volume does not mean that each module meets the standard. Point-by-point measurements can reveal distribution problems.

Confirm the fan margin. Adding new filter sections will increase system resistance. Whether the fan can maintain the target air volume needs to be calculated based on the actual resistance curve. For specific methods, please refer to Discussion of how much the added resistance of the chemical filter will increase the fan's electricity consumption .

Check export targets. Qualified air volume does not mean that the gas treatment effect is up to standard. The outlet concentration needs to be tested separately. involving the MAU box-type chemical filter , it is recommended to set up sampling ports before and after the filter section to facilitate tracking. For the fresh air project of

Treatment effects cannot be inferred from the number of modules alone. Installing a sufficient number of modules does not mean that the system capability is sufficient. The actual effect depends on air volume distribution, media status and operating conditions.

Project judgment example

A certain fresh air system needs to add a chemical filtration section, with a total air volume of 30,000 m³/h. The preliminary plan uses four modules connected in parallel.

During model selection, we found that if we simply divide the total air volume by 4, each module can handle 7500 m³/h. However, the air inlet distribution inside the frame is uneven. The actual air volume of modules close to the air inlet side may be higher, while the air volume of modules farther away from the air inlet side may be lower. At the same time, the resistance differences of each branch will also affect the distribution.

Adjustment plan: Optimize the air inlet distribution during frame design, and set adjustment dampers on each branch. After installation, the air volume is measured module by module, and the air volume of each module is adjusted to be close to the design value. After confirming that the air volume is evenly distributed, verify the outlet concentration.

This case shows that the parallel system cannot simply distribute the air volume evenly according to the quantity, but must consider the actual distribution situation. involving When selecting a chemical filter product series , it is recommended that the system structure and air volume distribution requirements be provided to the supplier for verification.

Key points for selection and acceptance inspection

About Aili Industrial’s air volume selection support

The core of air volume selection of chemical filters is to match the system structure, module allocation and actual working conditions.

Aili Industrial has independent manufacturing capabilities in filters, motors, fans, control systems and sheet metal processing, and can provide chemical filter product series and supporting air supply equipment. For projects that require multi-module configuration, the system air volume, frame layout and branch structure can be combined to assist in checking the single-module air volume and distribution plan. When the filter is matched with MAU, FFU, EFU and other equipment, the resistance, interface and maintenance methods can be confirmed uniformly.

Related products:Chemical filter product series、MAU box chemical filter、FFU comes with chemical filter . When enquiring, provide the system air volume, module number and structural conditions to help confirm the appropriate air volume selection plan. The specific selection is subject to the technical documents and test results confirmed by the project.