What particle problems can airflow short circuits cause?

Airflow short circuit is a common but easily overlooked problem in clean systems. Its performance is: the air supply volume seems to be sufficient and the equipment is running normally, but the particle concentration at the workstation is high, recovery is slow, or regional differences are obvious. The reason is that the supply air does not effectively pass through the protected area and leaves from the nearby return air outlet or exhaust outlet.

To determine an airflow short circuit, you should not only look at the total air volume, but also the actual path of the air. The following will focus on the causes of short circuits, particle manifestations, troubleshooting methods, and rectification directions.

First understand the conditions for the formation of air flow short circuit

Airflow short circuits usually occur when:

• The distance between the air supply vent and the return air vent is too close, and the air takes a shortcut to leave;

• The return air outlet or exhaust outlet is located near the supply air jet to remove the protective air flow;

• Equipment or structures block the airflow from reaching the remote workstation;

• Room openings or gaps create low-resistance passages through which air escapes from nearby areas;

• The local exhaust volume is too large, and the suction direction conflicts with the air supply direction.

These conditions may exist individually or together. When a short circuit occurs, the total air volume may still meet the standard, but the effective ventilation is insufficient.

The total air volume is sufficient but the particle removal at the workstation is insufficient.

The most typical manifestation of an airflow short circuit is: the total air volume of the system appears to be normal, but the particle concentration at the workstation is high or the recovery is slow. This is because the air does not actually pass through the workstation and the pollutants are not effectively taken away.

If you only check the total air volume and equipment operating status, you may not find the problem. It is necessary to observe the actual path of the air flow and confirm whether the air passes through the protected area before leaving. The problem of average wind speed masking local differences can be referred to Why does the measured average wind speed not mean that the air flow is uniform?。

Slow recovery is a common symptom

If the particle concentration does not decrease for a long time after people enter, open the door, or generate dust temporarily, it may be related to air flow short circuit. Short circuits cause air to circulate in local areas, preventing pollutants from being discharged in time.

Slow recovery does not necessarily mean that the system has insufficient capabilities, but may also be caused by a wrong path. For detailed investigation, please refer to How to reduce local retention in non-unidirectional flow clean rooms? , first confirm whether the air flow covers the workstation.

Regional differences increase

Airflow short circuits can lead to increased differences in particle concentrations in different areas of the room. Areas close to return or exhaust vents may perform better, and areas further away from these locations may perform worse.

If it is found that certain workstations in the same room have high particles while other workstations are normal, check whether these workstations are within the scope of the airflow short circuit. For lateral interference identification in unidirectional flow areas, please refer to How to identify lateral interference in unidirectional flow areas?。

Exhaust air suction can aggravate short circuits

If the equipment exhaust, process exhaust or local exhaust hood is located close to the air supply surface or protected area, clean air may be directly drawn away, causing a short circuit. The greater the exhaust air volume, the more obvious the impact of short circuit.

When judging, you should compare the airflow changes when the exhaust is turned on and off to confirm whether the exhaust has removed the protective airflow. If exhaust is a necessary process condition, the air supply direction and exhaust position should be adjusted instead of simply turning off the exhaust.

The position and direction of the return air outlet are critical

Improper location of the return air outlet is a common cause of airflow short circuit. If the return air outlet is too close to the air supply outlet, the air will take a shortcut to leave; if the return air outlet is blocked, the air will be discharged through other paths, which may cause stagnation.

The return air vents should be evenly distributed and avoid being concentrated near the supply air jet. The return air direction should also be coordinated with the supply air direction so that the air can cover the work area before being discharged. For optimization of return air layout, please refer to How to convert the clean area area into air supply demand? , first confirm whether the air volume distribution is reasonable.

Airflow visualization helps identify short circuit paths

Airflow visualization is a straightforward way to identify airflow short circuits. Through smoke or tracer gas, the actual path of the air from the air supply surface to the return air outlet can be observed to determine whether it passes through the protected area.

When observing, you should pay attention to:

• Whether the air supply jet reaches the work station;

• Whether the air is diverted near the workstation;

• Whether there is a shortcut;

• The direction of airflow near the return air outlet.

Visualization should be carried out under actual operating conditions, covering equipment operation and personnel activity states. For boundary verification of open workstations, please refer to How to establish a local clean area in an open workstation?。

Measure air volume and pressure difference to assist judgment

Airflow visualization helps identify problems, and measurements help quantify changes. When measuring, please note:

• Record the air volume at the supply air outlet and return air outlet;

• Compare wind speed and direction in different areas;

• Check the balance between exhaust air volume and make-up air volume;

• Record the pressure difference changes.

If the return air volume is much greater than the air volume passing through the workstation, there may be a short circuit. If the exhaust air volume is too large, the protective airflow may be removed. For specific air volume calculations, please refer to How to convert face wind speed and air volume?。

Correction direction: adjust the path rather than blindly increment

After discovering a short circuit in the air flow, priority should be given to adjusting the air supply and return paths instead of simply increasing the air supply volume. Common rectification directions include:

• Adjust the position of the return air outlet to avoid the supply air jet;

• Adjust the exhaust position or air volume to reduce the suction of protective airflow;

• Add baffles or partitions to guide airflow through the workstation;

• Clear the obstructions on the return air duct;

• Adjust equipment layout to allow airflow to reach remote areas.

Airflow paths and particle trends should be re-verified after rectification. Insufficient maintenance channels will increase subsequent expenditures. This is reflected in what later expenses will be increased due to insufficient maintenance channels . There is a more detailed analysis of

Equipment selection and terminal matching

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.

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. 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?。

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

Project judgment example

The total air volume of a certain project reached the standard, but the particles at the workstation continued to be high. The investigation found that the return air outlet is located near the air supply jet, the air leaves via a shortcut, and the work station is in a weak protection zone. Adjustment method: Move the return air outlet to the opposite side of the workstation, so that the airflow passes through the workstation and then is discharged. After adjustment, the particles at the station decreased.

In another project, the wind speed at the workstation dropped after the exhaust air of the equipment was turned on. The investigation revealed that the exhaust air volume was too large and the protective airflow was taken away. Adjustment method: Adjust the exhaust position and air volume, and increase supplementary air so that the air supply can cover the workstation. The wind speed recovers after adjustment.

These two situations illustrate that airflow short circuit will cause the problem of sufficient total air volume but insufficient protection, which needs to be investigated and rectified based on the actual path.

Key points for selection and acceptance inspection

Aili industrial equipment supporting support

Air flow short circuit is often not caused by insufficient air volume, but by incorrect path. Aili Industrial has collaborative capabilities in fans, motors, filters, control systems and complete machine assembly links. It can combine the project's return air layout, exhaust conditions and workstation locations to check the equipment layout, air flow path and operation settings to help determine whether to adjust the position of the return air outlet, change the exhaust direction or optimize the air supply form, rather than just adding equipment based on the total air volume. Specific models can be viewed FFU clean air supply products , supporting equipment can be viewed EFU equipment end fan filter unit , please refer to the filter package. HEPA and ULPA filters。