The clean shed is open all around, how to judge whether the chemical filtration is effective?

A clean shed is different from a closed clean room. It may be open on all sides or only partially enclosed. People, materials, and air from adjacent areas can enter freely. In this case, if the chemical filtration section is installed, how to judge the effect?

Direct answer: You can’t just look at the outlet concentration of the filter section, but also look at the gas concentration and airflow coverage at key locations in the shed.

The low concentration at the outlet of the filter section indicates that the part of the air that passed through the filter section has been processed. However, if untreated air enters from an open boundary or a backflow dead zone is formed in the shed, the gas concentration at the target location may still be high. For specific differences, please refer to Discussion of the difference between chemical filters and HEPA filters .

Identify open boundary inputs

The clean shed is open on all sides, meaning the boundaries are not sealed.

Personnel access and operations. The operator's hands, clothing, and tools may introduce gas or particles. When entering and exiting frequently, the amount of external air exchange increases.

Airflow in adjacent areas. If there are other processes or equipment next to the clean shed, the released gaseous pollutants may enter laterally. Wind direction and pressure differential determine the input. For specific partitioning methods, please refer to Discussion on how odors in multi-story factory buildings interact with each other and how chemical filtration should be partitioned .

Material transfer. Open containers or packaging may release gas as materials are moved in and out. If the material itself has odor or volatility, this part of the load will not pass through the filter section.

Fresh air from outside. If the fresh air in the room where the clean shed is located is not treated, gaseous pollution input from the outside will also enter the shed.

The main input pathways should be identified before determining whether the chemical filtration section can cover these pathways. For specific investigation methods, please refer to whether to do air sampling before choosing a chemical filter . Discuss

Clarify the scope of protection

To judge the effect, you must first determine what to protect.

Partial protection or whole shed air. If you are only protecting a certain workstation or equipment in the shed, the sampling point should be set near that location, rather than just looking at the average concentration in the shed. If the target is the entire shed air, sampling points need to cover a representative area. For specific sampling methods, please refer to Discussion of sampling points for chemical filter performance verification .

Where are the key locations. Product exposure areas, operating breathing belts, and air inlets of sensitive equipment may have different control requirements. Sampling points need to be determined separately.

One reading cannot represent the entire space. The airflow organization of an open clean booth is uneven and may be different between the edges and the center, and between the upper and lower parts. Sampling points should reflect actual differences.

What is the target gas? Is it acidic gas, alkaline gas, organic vapor or odor? Different components correspond to different detection methods and filter media. For specific principles, please refer to Discussion on why chemical filters should be selected according to the target gas .

Compare exit and shed

To judge whether chemical filtration is effective, you need to look at the concentration at the outlet of the filter section and in the shed at the same time.

Filter section outlet. Measure the air concentration after passing through the chemical filtration section. This data reflects the processing capabilities of the filter segment itself. If the outlet concentration is already high, it means that the filter material may be consumed or the selection is inappropriate. For specific differences, please refer to Discussion of the difference between initial efficiency and lifetime efficiency of chemical filters .

Key locations in the shed. Measure the gas concentration near the protected target. If the outlet of the filter section is normal but the key position in the shed is high, it means that untreated air has entered or the air flow coverage is insufficient.

Boundary input comparison. If conditions permit, measure the gas concentration near the open boundary to determine the degree of influence of external inputs.

The data should correspond to the same working conditions. Record the air volume, operating mode, personnel activities and door zone status during sampling. For specific verification methods, please refer to Discussion of whether chemical filter validation is required to maintain consistent production loads .

Check airflow coverage

The air flow organization of the open clean booth directly affects the filtration effect.

Air supply coverage. Does the air outlet surface of the chemical filter section or supporting air supply equipment cover the protected area? If the supply air only blows to part of the area, other locations may not get the treated air. For specific configuration, please refer to Discussion of what localized contamination can be treated by FFU plus chemical filter .

Whether the airflow is blocked. Equipment, tools, and personnel may block airflow and create localized stagnation areas. It is necessary to observe the actual air flow direction, or measure the wind speed at different locations.

Is there a short circuit? If the supply air blows directly to the return air outlet or open boundary without passing through the protected area, the filtration effect will be compromised. For specific air volume distribution, please refer to Discussion on whether the chemical filter air volume should be selected based on the total air volume of the system or the air volume of a single unit .

pressure difference relationship. If the clean shed is at a positive pressure relative to the outside, the amount of outside air entering will be reduced. If the pressure differential is insufficient or negative, the input to the open boundary increases. For specific pressure difference control, please refer to Discussion of how chemical filter modification can avoid affecting room pressure differential .

Comparing structural and source measures

If the effect is not satisfactory, the treatment direction is not necessarily just to increase filtering.

Improve fencing. Adding partial enclosures or soft curtains can reduce the direct entry of outside air. But be aware of the impact on operation and maintenance.

Adjust adjacent exhaust air. If gaseous pollution is released in adjacent areas, strengthening local exhaust can reduce the spread to the clean shed. For specific configuration, please refer to Discussion on why EFU needs supporting chemical filters .

Optimize the air supply position. Adjust the installation position and direction of the chemical filter section or air supply equipment to allow the treated air to cover the protected area first.

Chemical filtration solutions still need to meet air volume and cleanliness requirements. After adding a filter section or adjusting the structure, the air volume and resistance need to be rechecked. For specific calculations, please refer to Discussion of how much the added resistance of the chemical filter will increase the fan's electricity consumption .

Project judgment example

A clean shed is open all around and has a chemical filtration section inside to process organic solvent vapor. The concentration test at the outlet of the filter section was normal, but the operator reported that there was still an odor in the shed.

The investigation found that the smell came from the solvent use station in the adjacent area and laterally entered the clean shed through the open boundary. The chemical filtration section only treats the circulating air within the shed and does not cover the external input.

Adjustment plan: Increase local exhaust in adjacent areas to reduce diffusion to the clean shed; at the same time, add soft curtains at the open boundary of the clean shed to reduce lateral air flow exchange. After the adjustment, the smell in the shed was significantly improved, and the concentration at the outlet of the chemical filtration section remained normal.

Another project improved the protection effect by adjusting the air supply direction so that the treated air first passes through the operating station and then flows to the open boundary.

These two cases illustrate: To judge the chemical filtration effect of an open clean shed, we need to look at the outlet of the filter section, as well as the key locations and airflow coverage in the shed. involving When selecting a chemical filter product series , it is recommended that the protection range, boundary conditions and system parameters be provided to the supplier for verification.

Key points for selection and acceptance inspection

About Aili Industrial’s clean shed filtration package

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 open clean shed projects, the protection scope, boundary conditions, air flow organization and target gas can be combined to assist in checking the chemical filtration section configuration and effect verification plan.

Related products:Chemical filter product series、MAU box chemical filter、FFU comes with chemical filter . Provide protection range, boundary conditions and target gas when enquiring, which will help confirm the appropriate solution. The specific selection is subject to the technical documents and test results confirmed by the project.