Will the increased resistance of the FFU high-efficiency filter reduce the wind speed?

Yes, but not all decreases in wind speed can be attributed to drag.

This problem is particularly common after replacing the filter element: the unit does not move, the controller parameters do not change, but the wind speed is lower than before. The first reaction on site is often 'the new filter element has too much resistance.' This judgment may be correct, or it may lead to a wrong direction.

The increase in filter element resistance will indeed change the fan operating point, but there are other possibilities for the decrease in wind speed. First figure out which category it is, and then decide how to deal with it.

First look at the temper of the fan

FFU mostly uses centrifugal fans equipped with EC or DC motors. The characteristics of this type of fan are: when the system resistance increases, the operating point moves to the left along the fan curve, the air volume decreases, and the static pressure increases. This is a characteristic of the fan itself, not a fault.

Therefore, if the resistance of the replaced H14 is higher than that of the original H13, but the controller gear position has not changed, the decrease in wind speed is an expected phenomenon. The question is how much it drops and whether it can maintain the target surface wind speed.

The judgment method is very straightforward: get the resistance data of the new filter element at the target air volume, and compare it with the PQ curve of the fan to see where the new working point falls. If the landing point is still within the range corresponding to the target wind speed, the plan is established; if it has deviated, it cannot be simply solved by 'increasing the speed' - increasing the speed may bring about chain changes in noise, vibration and motor load.

It is not a problem of resistance, it will also be manifested as a decrease in wind speed.

In the following situations, the differential pressure gauge looks normal, but the wind speed does not increase:

The filter element is installed backwards. For products with protective nets or airflow direction requirements, the state of the air inlet surface will change after the installation is reversed, and the wind speed distribution will be uneven. The performance is that the local surface wind speed is low, the average value looks okay, but the uniformity becomes worse.

The air intake of the unit is blocked. If there are cables, bridges, air ducts or ceiling structures above the FFU close to the air inlet, the air inlet resistance will increase, and the effect is similar to the increase in filter element resistance. This type of problem is more common on newly installed or renovated units.

Measurement methods are inconsistent. The anemometers used before and after changing the filter element are different, the measuring point locations are different, and the stabilization time is not enough, so the readings themselves are not comparable. This happens more often than imagined.

Controller or power supply status change. The gear display is the same, but the actual output may not be the same. If a certain unit in the group control system communicates at an abnormal speed, it may not be discovered just by looking at the panel.

Processing order recommendations

Restore comparable conditions first, and then determine the cause.

Specific methods: confirm that the old and new data are obtained at the same gear, the same measuring point, and similar environmental conditions; check the resistance report and installation direction of the new filter element; check whether there is any new obstruction in the air inlet space of the unit; confirm that the controller output and communication status are normal.

After completing these steps, the problem can basically be located in the filter element selection, installation status or control link. The least recommended approach is to directly increase the speed. Increasing the rotational speed can indeed bring the wind speed back temporarily, but the system resistance does not change, and the motor load, noise and vibration will also change. Long-term operation is not cost-effective, and the real reason is concealed.

If it is confirmed that the filter element resistance is too high and the fan margin is insufficient, there are several treatment directions: replace the filter element with a larger effective filtration area, adjust the unit configuration, or recalculate the target wind speed within the scope allowed by the project. These require looking at the fan curve and filter element resistance together during the selection stage.

About Aili Industrial’s FFU package

Aili Industrial's FFU ranges from motors, fans, and control systems to HEPA/ULPA air filters are all manufactured independently, and the core components are matched in the same system. This means in During the FFU fan filter unit selection stage, the filter element resistance and fan operating point can be calculated together, instead of purchasing them separately and then trying your luck on site.

For projects that are already in operation, if the wind speed drops after replacing the filter element, the original unit model, old and new filter element parameters, and actual measured wind speed records can be provided to facilitate comparison with the fan curve to determine where the problem lies. Device-side applications such as The internal space of the EFU equipment-side fan filter unit is more compact, and the air inlet conditions are different from those of FFU. Equipment structural factors should also be considered when troubleshooting.