At which points should sampling be conducted for chemical filter performance verification?

After the chemical filter is installed, the effect will ultimately be determined by sampling and testing. But where the sampling points are chosen directly determines what questions the data can answer.

If you choose the wrong point, the data may look normal but cannot explain the actual problem. For example, if you only measure one point at the filter outlet and without inlet data, you cannot judge the removal efficiency; if you only measure the total return air and not the protection area, you cannot tell whether the target location meets the standard. For specific efficiency calculation methods, please refer to Discussion on how to calculate the removal efficiency of chemical filters .

First distinguish between filter segments and regional purposes

Before sampling, first clarify what questions the test will answer.

To evaluate the filter section itself , paired inlet and outlet sampling is required. The removal efficiency is obtained by subtracting the outlet concentration from the inlet concentration and dividing by the inlet concentration. Only the exit is measured, there is no reference to the entrance, and the data is incomplete.

To evaluate the protection effect , sampling is required in target areas or key workstations. If the outlet concentration of the filter section is qualified, it does not mean that the gas concentration in the protective area also meets the standard. The airflow organization in the area and the location of the pollution sources will affect the final result.

The two types of data have different meanings and cannot be mixed into the same efficiency indicator. The filter section efficiency reflects the filter performance, and the regional concentration reflects the actual protection effect. It is recommended to sample and record separately during acceptance. For specific differences, please refer to Discussion of what breakthrough concentration means in a chemical filter report .

Filter section sampling: inlet and outlet pairing

If the purpose is to evaluate the effect of the filter section, the sampling points should cover the inlet and outlet.

Inlet sampling point. It is located upstream of the filter section, close to the air inlet surface of the filter, and avoids elbows, valves or local exhaust outlets. The inlet concentration should represent the gas load entering the filter section. If there are multiple branches at the entrance, you need to confirm whether the concentration of each branch is consistent.

Exit sampling point. It is located downstream of the filter section and close to the air outlet surface of the filter. The outlet concentration reflects the filtered gas level. The outlet sampling point should avoid the bypass air leakage location, otherwise the data may be low.

Paired sampling. The inlet and outlet should be collected at the same time period as much as possible to avoid inability to correspond to the data when the inlet concentration fluctuates. If the inlet concentration changes significantly, a synchronization or time matching scheme is required. For specific methods, please refer to Discussion on how to calculate the removal efficiency of chemical filters .

Number of sampling points. For large cross-section filter sections, a single point may not be representative. Multiple sampling points can be set up at the inlet and outlet, averaged, or evaluated by cross-section zoning.

Area Sampling: Protect Target Locations

If the purpose is to evaluate the protection effect, the sampling points should be located around the target area.

Key work stations. Sampling points should be set up for gas-sensitive equipment or operating locations. For example, near photolithography equipment, precision assembly stations, and product exposure areas. For specific applications, please refer to Discussion of which contaminants should be focused on in photolithographic area chemical filters .

Return air area. The return air concentration can reflect the overall level of regional air. If there are multiple return air outlets in the area, you need to confirm whether the concentration is consistent. For specific differences, please refer to whether data center chemical filters should handle fresh air or recirculated air . The discussion of

New outlet and background. If external input is the primary source, fresh air outlet sampling can determine the pollution load entering the system. Background sampling can eliminate the influence of environmental background.

Points must be representative. Avoid being close to local exhaust outlets or pollution sources, and avoid locating them in dead corners of airflow or in locations where untreated air interferes. Sampling points should be representative of actual conditions in the area or target. For specific sampling methods, please refer to whether to do air sampling before choosing a chemical filter . Discuss

Time and working conditions must match

After the sampling point is selected, the sampling timing and working conditions must also be aligned.

Covers representative time periods. If production is intermittent, sampling times should include periods when contamination occurs. Data measured during pollution-free periods cannot represent the actual load. For specific methods, please refer to Discussion of how to set clear success conditions for chemical filter trials .

Record operating conditions. The air volume, temperature and humidity, production status and ventilation method during sampling should be recorded. This information can help determine the representativeness of the data. For specific differences, please refer to Discussion of the difference between initial efficiency and lifetime efficiency of chemical filters .

Avoid changing other conditions at the same time. If the air volume is adjusted, materials are replaced, or production shifts are changed at the same time during the sampling period, data changes may come from these factors and may not necessarily reflect the actual performance of the filter.

Repeat sampling. For key points, it is recommended to repeat sampling at different periods of time to confirm the stability of the data. Single data may be random.

Prevent sampling self-bias

The sampling process itself may also affect the results.

Pipe material. The sampling line material should be compatible with the target gas to avoid adsorption or release. Some gases are sensitive to pipeline materials, and appropriate materials need to be selected.

Pipe length. A sampling pipe that is too long may cause gas to adsorb or react on the pipe wall, affecting concentration readings. Try to shorten the pipeline as much as possible, or confirm according to the method requirements.

Detection limit. For low concentration projects, the detection limit of the detection method must meet the requirements. When the outlet is lower than the detection limit, it should be explained according to the method and cannot be written directly as zero concentration. For specific differences, please refer to Discussion of why chemical filter performance reports list specific target gases .

Background control. Before sampling, confirm the environmental background concentration and set up a blank sample if necessary to eliminate interference introduced by the sampling process.

Project judgment example

After the chemical filter of a certain project was installed, only one point was measured at the outlet, and the data showed that the concentration was very low. However, after running for a period of time, the protected area still reflects an odor.

The investigation found that the outlet sampling point was located directly behind the filter section, but the protection area was affected by another air flow path and did not pass through the filter section. Only the exits are measured, which cannot reflect the actual conditions of the protected area.

Adjustment plan: Add sampling points in the protection area and key work stations, and simultaneously detect the inlet and outlet of the filter section to confirm the efficiency of the filter section. After additional sampling, it was found that the gas concentration in the protected area was indeed high, and the source was related to the bypass air flow. After re-testing, the regional concentration dropped.

This case illustrates: the sampling point location must correspond to the detection purpose, and the filter section efficiency and regional effect need to be confirmed separately. involving When selecting chemical filter product series , it is recommended to provide the sampling plan and point layout to the supplier for verification.

Key points for selection and acceptance inspection

About Aili Industrial’s sampling and testing packages

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 performance verification, the target gas, filter section structure, protection area and system conditions can be combined to assist in checking the sampling point layout plan. When the filter is matched with MAU, FFU, EFU and other equipment, the location and maintenance method of the sampling port can be confirmed uniformly.

Related products:Chemical filter product series、MAU box chemical filter、FFU comes with chemical filter . Providing the detection purpose, target gas and system conditions when inquiring will help confirm the appropriate sampling plan. The specific selection is subject to the technical documents and test results confirmed by the project.