How to read the FFU fan curve? Why should we also look at the filter resistance curve?

The fan curve and resistance curve should be viewed together

In FFU selection, fan performance curve is a common reference. The fan curve describes the static pressure that the fan can provide at different air volumes. However, looking at the fan curve alone, the actual operating point of the FFU cannot be determined. Because the actual air volume of FFU also depends on the system resistance, including filter resistance, box resistance and external system resistance.

To determine the actual operating point of the FFU, the fan curve and the system resistance curve need to be looked at together. The intersection of the two curves is the actual working point. If you only look at the fan curve, you may overestimate or underestimate the actual air volume.

Therefore, when reading FFU performance data, both the fan curve and the resistance curve should be confirmed. Aili Industrial will explain the conditions corresponding to the curve during FFU complete machine testing and parameter compilation. For the basic structure of the FFU machine, please refer toAili Industrial FFU fan filter unit。

What does the fan curve describe?

The fan curve describes the pressure the fan can provide at different air volumes. Usually includes static pressure curve, total pressure curve or power curve. The horizontal axis is air volume, and the vertical axis is pressure or power.

Fan curves correspond to specific speeds and air densities. If the rotational speed or air density changes, the curve will also change. When reading, confirm the rotation speed, air density and test conditions corresponding to the curve.

The fan curve test object is the fan body, excluding the FFU box and filter. Therefore, the fan curve cannot directly represent the performance of the FFU machine.

What does the resistance curve describe?

The resistance curve describes the resistance of the system at different air volumes. For FFU, system resistance includes filter resistance, box internal resistance, air supply path resistance and external system resistance. The filter resistance is related to the air volume. When the air volume increases, the resistance usually increases.

Resistance curves are usually differentiated by filter status. The new filter has lower resistance, and the resistance increases after dust accumulation. If the project needs to account for the performance of the filter over its lifetime, resistance curves can be plotted separately for new filters and dust-filled filters.

How to determine the working point

The operating point is the intersection of the fan curve and the resistance curve. At the intersection point, the pressure provided by the fan is equal to the system resistance, and the air volume reaches equilibrium. The intersection points correspond to the actual operating air volume and pressure.

If the operating point corresponding to the target air volume is located in the efficient area of ​​the fan curve, the fan operation is more reasonable. If the operating point is close to the edge of the fan curve or outside the range, the efficiency may be lower or the target air volume cannot be achieved.

The operating point also changes as dust accumulates on the filter. After the filter accumulates dust, the resistance curve moves upward and the operating point moves toward the low air volume direction. If the FFU adopts constant speed control, the air volume will decrease. If constant air volume control is adopted, the fan speed will increase and the working point will move towards the high speed curve.

How to distinguish the data of bare air blower and complete machine

When reading the curve, you should confirm whether the data belongs to the bare fan or the complete unit. The bare fan curve only includes the fan body, and the complete machine curve includes the box and filter. If you use the bare fan curve to estimate the air volume of the whole machine, the result may be on the high side.

If the manufacturer provides the complete machine curve, the filter configuration and test conditions corresponding to the curve should be confirmed. The overall curves of different filter configurations are different.

How to evaluate margin

When evaluating margin, you can look at the relationship between the target operating point and the fan curve. If the target operating point is located in a flatter area of ​​the fan curve, the pressure change will be smaller when the air volume changes. If it is located in a steep area, pressure changes will have a greater impact on the air volume.

The margin should also take into account the change in operating point after the filter accumulates dust. If the working point can still meet the target air volume after dust accumulates on the filter, it means that the margin is sufficient. If the air volume drops significantly after dust accumulation, you may need to choose an FFU with a larger fan capacity or shorten the filter replacement cycle.

Issues that should be confirmed in advance during project communication

During the verification phase of the FFU fan curve and resistance curve, it is recommended to confirm the following with the manufacturer: whether the curve corresponds to a bare fan or a complete machine; the rotation speed and air density corresponding to the curve; the filter configuration and resistance curve; the target air volume and working point; the change in the working point after dust accumulation on the filter; the margin evaluation method; and whether on-site test verification is required.

If you are checking the FFU fan curve, you can visitAili Industrial FFU fan filter unit to learn about the complete machine configuration, you can also refer toFFU is equipped with ULPA ultra-high efficiency filter to learn about the filter resistance characteristics, or contact Aili Industrial for curve support.

in conclusion

The actual operating point of FFU is determined by the fan capacity and system resistance. When reading the performance curve, you should confirm whether the curve belongs to a bare fan or a complete unit with a filter, and then determine whether the target air volume can be achieved under the agreed resistance. The fan curve and resistance curve should be viewed together, with the operating point changing as the filter accumulates dust. Margin evaluation needs to consider the entire life cycle.

Aili Industrial has complete production capabilities in FFU complete machine testing and parameter compilation, and can explain the conditions corresponding to the curve. If you need to know more about the FFU performance curve, you can visitAili Industrial FFU fan filter unit , you are also welcome to contact Aili Industrial for project support.