How do HEPA and ULPA match cleanliness goals?

How to choose between HEPA and ULPA is a question that often arises in cleaning projects. Many projects will directly ask: Is ULPA necessary for ISO 5? Is H13 enough for ISO 7? There is no universal answer to these questions because filter selection depends not only on the room rating but also on process-sensitive particle size, allowable particle levels, background loading, system resistance, and installation sealing conditions.

Simply equating the cleanliness target with the filter model will easily lead to two extremes: not upgrading the areas that should be upgraded, or using the highest level for the entire site. As a result, the fan cannot be driven, the resistance is too high, and the operating cost increases. The following will start from the following links: target definition, filtering requirements, complete machine matching, and on-site verification.

First distinguish between particle targets and filter levels

Cleanliness levels describe the concentration of air particles in a specified area, specified particle size, and occupancy conditions. Filtration efficiency describes the ability of a filter to reduce particle penetration under specified test conditions. The two are related, but not the same concept.

If you are still unclear about the difference between space rating and filter efficiency, you can read What is the difference between cleanliness level and filtration efficiency ? Let’s first clarify this basic concept. The cleanliness level must also indicate the measured particle size. For specific reasons, please refer to Why must the particle size be indicated in the cleanliness grade?。

HEPA and ULPA are filter ratings, not room rating labels. In the same ISO 5 area, different filtration solutions may be used due to different process-sensitive particle sizes, background loads and equipment structures. You cannot specify a filter model based on the ISO number alone.

Clarify filtration needs from contamination risks

Before choosing a filter, make sure of three things:

• Sensitive particle size : Which particle size is the product most sensitive to, whether it is 0.3μm, 0.1μm or smaller;

• Background loading : Concentration and sources of particles in the air upstream of the filter;

• Allowable Level : The level of particles allowed on a product surface or critical area.

If the process is particularly sensitive to tiny particles, it may be necessary to add control indicators and detection capabilities, and then compare HEPA and ULPA configurations. If the background load is low and the product-sensitive particle size is large, a suitable HEPA solution may also meet the requirements. For specific judgment, please refer to Is ULPA mandatory for ISO Level 5 projects?。

When it comes to protecting the interior of the device, there is also a combination of cavity airflow paths and exposure times. Can be referenced How to plan clean air supply for closed equipment cavities? , first confirm the protection boundary, and then determine the filtering level.

The filter efficiency report should clearly read the test particle size

When comparing HEPA to ULPA, you can't just take a percentage. The test particle size in the efficiency report should be read in conjunction with the adopted standard, test method and air volume. The fixed particle size results and the most penetrable particle size results are not the same caliber.

For specific readings, please refer to How to read the test particle size in the filter efficiency report? . If one report writes about 0.3μm efficiency and another reports on MPPS classification, it cannot be sorted directly by percentage. The test caliber should be unified first.

High-efficiency configuration requires checking the matching of the entire machine

Higher efficiency filters tend to have higher resistance. After switching to ULPA, if the fan operating point remains unchanged, the actual air volume may decrease, resulting in insufficient terminal wind speed or insufficient air changes.

When selecting, you should check:

• The initial resistance and final resistance of the filter at the target air volume;

• The working point of the fan under corresponding resistance;

• Whether the input power and noise of the whole machine are still within the allowable range;

• Whether the installation space accommodates thicker or denser filters.

If the filter area is insufficient, the fan may require higher pressure to maintain flow. For details, please refer to How does insufficient filter area affect fan selection? . If the wind speed facing the filter is too high, it may also increase resistance, power consumption and noise. Please refer to What will be the impact if the wind speed facing the filter is too high?。

The rated air volume must match the actual operating air volume

The rated air volume of the filter is used to describe its specified test or design conditions. The actual operating air volume should fall within the usage range confirmed by the manufacturer. When selecting a model, you need to check the efficiency, resistance, and fan operating point. You cannot determine replacement based on the same size.

For specific judgment, please refer to How does the filter's rated air volume match the actual operating air volume? . If the air volume drops after replacing the filter, you should first check the operating point instead of directly increasing the rotation speed.

Filter thickness and structure are not equal to resistance

Increasing filter thickness does not necessarily reduce resistance. The pressure drop is determined by the characteristics of the filter material, folding structure, filter area, air volume and internal support. Specific model data under the same working conditions should be used for comparison. Resistance or service life cannot be inferred from the appearance thickness. Related analysis can refer to Does increasing filter thickness definitely reduce resistance?。

Sealing and installation leak detection cannot be omitted

If the high-efficiency filter is not properly installed and sealed, bypass leakage will allow unfiltered air to enter the clean side. At this time, upgrading ULPA cannot achieve the expected results. After installation, the frame seal, installation interface and leak detection conditions should be checked.

If there are abnormal particles on site but the filter efficiency is acceptable, priority should be given to checking the sealed bypass and airflow short circuit. Can be referenced Does higher filtration efficiency necessarily lead to improved site ratings? and What particle problems can airflow short circuits cause?。

Initial resistance and final resistance are used for different judgments

The initial resistance usually describes the pressure drop of a new filter under a specified air volume, and the final resistance is used to judge maintenance or replacement during the agreed use period. The final resistance is not the only life criterion. Damage, moisture, process risks and actual air supply capacity must also be considered.

For specific judgment, please refer to What are the initial resistance and final resistance used to judge? . If the operating pressure differential is abnormally low, a breakage or bypass should be investigated rather than a performance improvement.

Scenario judgment: It is not necessary to upgrade the entire room uniformly

Local areas of key equipment and room background areas may use different filtering configurations, and the working conditions should be evaluated separately. There is no need to upgrade ULPA in the entire room because of high local requirements.

For example, ISO 5 is written in the ordinary background area and inside the precision equipment, but the process-sensitive particle sizes are different, and the filter selection may be different, and the technical conditions should be formed separately. For the filtration configuration of open work stations or local protected areas, please refer to How to establish a local clean area in an open workstation?。

Equipment selection and terminal matching

Filter selection should correspond to target particle size and actual resistance.The HEPA and ULPA filter pages have parameters for different levels of products. When selecting, check the efficiency of the specific model at the target air volume.

Please refer to the room background air supply FFU clean air supply products , please refer to the local protection of the equipment side. EFU equipment side fan filter unit . The logic of division of labor between the two lies in The division of labor between device-side EFU and room FFU is explained in detail.

If multiple devices require partition duty and troubleshooting, they can be combined FFU group control system provides unified management.

Project judgment example

A certain project originally used H14, but the user proposed to upgrade all projects to U15. After checking, it was found that the background load in some areas was not high, and the sensitive particle size of the product did not reach the level requiring U15; however, higher filtration configuration was indeed required inside key equipment. Adjustment method: Use U15 in key areas and check the fan working point, and retain H14 in the background area. After adjustment, the system resistance is controllable and the key areas meet the requirements.

Another project directly replaced the ULPA filter without checking the fan capacity. After installation, the terminal wind speed dropped. Adjustment method: Check the working point under the initial resistance of the new filter, adjust the fan speed and confirm that the power and noise are within the allowable range. After adjustment, the air volume and filtration efficiency are both satisfied.

These two situations illustrate that the selection of HEPA and ULPA must be comprehensively judged based on process objectives, background load, system resistance and installation conditions, and cannot be specified solely based on room grade or industry habits.

Key points for selection and acceptance inspection

Aili industrial equipment supporting support

The selection of HEPA and ULPA is often stuck between 'one level higher efficiency' and 'the fan cannot be driven'. Aili Industrial is responsible for air filters, fans, motors, control systems and complete machine assembly at the same time. It can check the filter efficiency, rated air volume, actual resistance, sealing method and complete machine working point in the same configuration table to avoid insufficient end wind speed after the filter is upgraded, or over-configuration of the background area to increase long-term operating costs. Specific filter parameters can be viewed HEPA and ULPA filters , the complete machine package can be viewed FFU clean air supply products and EFU equipment side fan filter unit。