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

The primary-efficiency and medium-efficiency filtration of the air-conditioning box should be configured hierarchically according to the system objectives and downstream component protection tasks. The front stage bears larger particles and part of the dust load, and the rear stage further reduces the particle load; the specific grades and combinations need to be confirmed based on the actual air conditions and the evaluation system adopted, and you cannot just pursue more stages.

Let each level have clear protection objects

First explain whether coils, fans, chemical media or subsequent high-efficiency filters need to be protected, and then assign tasks to each level. An overly dense front stage may increase resistance and replacement costs, and insufficient front stage capacity will cause the rear stage to accumulate dust faster. When comparing combinations, you should look at the rated air volume, initial resistance, dust holding capacity and replacement conditions, not just the name arrangement.

The inlet pre-filtration handles coarser particles and reduces the dust load in the rear section; the intermediate filtration further reduces particles under the agreed particle size evaluation conditions; the system support involves graded pressure difference monitoring, sealing and actual replacement of channels. Each level should have testable responsibilities, rather than a general 'more layer is safer'. How the inlet air condition affects the selection of filtration level can be referred toHow to select the air conditioning box filter grade based on the inlet air conditions?。

What problems do primary and intermediate effects solve respectively?

The primary filter mainly intercepts larger particles and protects the rear coil, fan and medium-efficiency filter itself. The medium-efficiency filter further reduces the fine particle load and provides pre-protection for the terminal high-efficiency filter or clean air supply. The relationship between the two levels is load sharing, not simple superposition. When the initial dust holding capacity is insufficient, the intermediate efficiency will accumulate dust in advance; when the intermediate efficiency is too high and the primary protection is insufficient, the replacement frequency of the intermediate efficiency may increase.

The structural differences between plate and bag filters will also affect the classification configuration. Please refer toWhat is the difference between plate and bag filters used in air conditioning boxes? . The effective area of ​​the bag filter is larger, and the dust holding and resistance performance are different from those of the plate filter. The selection should be compared under the same air volume and evaluation level.

The grading effect also depends on installation and maintenance.

Bypassing the installation frame will make the filter material grade meaningless, so the frame, sealing and compression structure must be checked together. Each level should be able to be monitored and replaced individually, and the total pressure difference cannot be used to replace all status judgments. The filtration combination will not alone determine the room cleanliness level, but also requires the cooperation of terminal, airflow and pollution source management.

Pressure difference monitoring is an important basis for judging replacement timing, but the pressure difference ranges and alarm values ​​of different levels need to be set separately. If only one total pressure difference is set, when the primary effect is blocked but the intermediate effect is acceptable, it will be difficult for maintenance personnel to judge which stage to change. The arrangement of the filter section before and after the fan will also affect sealing and maintenance. Please refer toWhat needs to be considered when arranging the filter section before and after the fan?。

The relationship between high-efficiency filtration and primary and secondary efficiencies

The high-efficiency filter at the end or the HEPA/ULPA of the clean air supply port relies on the front-stage filtration to reduce the dust holding pressure. When the primary and middle efficiency configuration is insufficient, the replacement frequency of the high-efficiency filter and the resistance rising speed will increase. On the contrary, if the primary and intermediate efficiency levels are too high but the actual air is cleaner, unnecessary resistance and maintenance costs may also be caused. Whether the high-efficiency filter should be placed inside the machine or at the end, please refer toShould the high-efficiency filter of the air-conditioning box be placed inside the machine or at the end of the air supply?。

When it is necessary to control gaseous pollutants, the division of labor between the chemical filtration section and the particle filtration section must also be clear. Please refer toWhat do the chemical filter and particle filter of the air conditioning box deal with respectively? . When the chemical media is sensitive to particles and droplets, the protective effect of the front-stage filtration needs to be checked.

What data to look at when comparing plans

When comparing different grading schemes, you should look at the efficiency, initial resistance, dust holding capacity and replacement pressure difference of each grade under rated air volume, rather than just looking at the grade name. Grades under different evaluation systems cannot be directly converted by letters or numbers. You should also pay attention to whether the filter frame size, installation depth and extraction space match the box body.

The selection of filter grade is also affected by the operating environment. Dust during construction, coastal salt spray or process dust may change the actual load. How to determine the maintenance cycle according to the operating environment, please refer toHow to determine the maintenance cycle of air conditioning box according to the operating environment?。

Aili industrial supporting equipment

Aili Industrial can check the filter and box installation frame as a set. When discussing classification, please clarify the downstream equipment that needs to be protected and the allowable system resistance. Aili Industrial has air filter manufacturing capabilities and can jointly confirm the filter size, filtration level, head wind speed, initial resistance and installation method with the air conditioning box structure; the manufacturing end covers motors, fans, control systems, sheet metal, air filters and complete machine assembly, and the graded pressure difference monitoring points and installation frames can be aligned in the same package.

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 filtration effect, applicable environment and replacement cycle 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.

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Related questions and answers

Is the higher the level of initial effect and intermediate effect, the better?
no. Increasing the level usually brings about increased resistance and replacement costs. It should be configured according to the inlet air conditions and downstream protection needs, rather than simply pursuing high levels.

Assuming only one total pressure difference, can we judge which stage should be replaced?
Not recommended. Differential pressure monitoring should be set up at each level to determine the dust accumulation status and replacement timing of the initial and medium effects.

Can Aili Industrial help configure the primary and medium effects?
The grading plan and installation frame can be checked based on the inlet air conditions, downstream protection objects and allowable resistance. The specific configuration needs to be confirmed according to the project conditions.

Related articles

1. How to select the air conditioning box filter grade based on the inlet air conditions?

2. What is the difference between plate and bag filters used in air conditioning boxes?

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

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

Key points for selection and acceptance inspection