FFU air volume hood measurement and wind speed conversion are inconsistent, how to check
Why are there differences between the two measurements?
There are two commonly used methods for FFU air volume measurement: one is to directly measure the air volume with an air volume hood, and the other is to measure the average wind speed on the air outlet surface and then multiply it by the effective air outlet area to convert the air volume. During acceptance or debugging, it is sometimes found that the results obtained by the two methods are inconsistent or even significantly different.
This inconsistency does not necessarily indicate abnormal FFU performance. The measurement principles, measuring point locations and calculation methods of air volume hood measurement and wind speed conversion are different. If the methods are not unified, the results will naturally be different. When troubleshooting, you must first check the measurement method, and then determine whether there is a problem with the equipment itself.
During the cooperation between FFU factory testing and on-site acceptance, Aili Industry will explain the caliber of air volume, wind speed and effective area to help the project party compare data under the same method. For the basic structure of the FFU machine, please refer toAili Industrial FFU fan filter unit。
How does the effective air outlet area affect the conversion results?
When calculating air volume using the wind speed conversion method, the average wind speed multiplied by the effective air outlet area is used. The value of the effective air outlet area directly affects the calculation results. If you use the box appearance area instead of the actual air supply area, the result will be higher because the box frame, sealing edge and non-air supply part are also taken into account.
The effective air outlet area usually refers to the net area of the actual air supply surface of the filter, excluding the portion occupied by the frame, beading and sealing structures. The effective air outlet areas of different FFU structures are different. For FFUs with the same dimensions, if the internal filter size or installation method is different, the effective air outlet areas may also be different.
When checking the two measurement results, it is recommended to first confirm whether the effective air outlet area used for wind speed conversion is correct. If the area value is too large, the converted air volume will be high; if the value is small, the converted air volume will be low.
How wind speed measurement points and measurement methods affect the results
The accuracy of the wind speed conversion method also depends on the measurement point layout and measurement method. The wind speed distribution on the outlet surface is usually not completely uniform, and the wind speed at the edges and corners may be lower than in the central area. If the number of measuring points is insufficient or the location is biased towards high wind speed areas, the average wind speed will be high; if the measuring points are biased towards low wind speed areas, the average wind speed will be low.
The response time, measurement direction and calibration status of the anemometer should also be confirmed during measurement. If the anemometer is not calibrated or has a mismatched range, the readings may be off. The measurement direction should be consistent with the direction of air flow to avoid errors caused by oblique measurements.
Air volume hood measurement also has its own conditions. The air volume cover needs to fit closely with the air outlet surface of the FFU. The cover itself will produce a certain amount of resistance, which may change the working point of the FFU. If the size of the cover does not match the FFU, or the seal is not tight, the measurement results will also be affected. The calibration status of the air volume hood and the reading stabilization time also need to be confirmed.
How does the additional resistance of the cover affect the working point?
When the air volume cover is placed on the FFU air outlet surface, it is equivalent to adding a section of resistance and flow channel changes to the air supply path. After the resistance of the FFU fan increases, the working point will move, and the actual air volume may be lower than the free air supply state. Different air volume hoods have different resistance characteristics. If the same FFU is measured with different air volume hoods, the results may be different.
Therefore, the air volume hood measurement value should be understood as the air volume under the hood conditions, rather than the absolute air volume of the FFU in the free air supply state. When comparing measurement data from different devices or at different times, the same air volume hood and the same measurement method should be used.
If the project requires air volume data that is closer to actual operating conditions, it can be corrected in conjunction with system resistance conditions, or other measurement methods can be used for cross-validation.
How to reconcile two measurement methods
When the air volume hood measurement is inconsistent with the wind speed conversion, you can check it by following the steps below. First confirm whether the effective air outlet area used for wind speed conversion is correct and check the actual air supply size of the filter. Then check whether the arrangement of wind speed measuring points covers the entire wind outlet surface, and whether the number and location of measuring points are reasonable. Then confirm the calibration status, range and measurement method of the anemometer and air volume hood. Then confirm whether the two measurements are performed at the same rotation speed and the same filter status. Finally, confirm whether the air volume cover matches the FFU air outlet surface and whether the seal is good.
If the above conditions are consistent and there are still obvious differences in the results of the two methods, you can repeat the measurement to confirm the stability, or use a third method for cross-validation.
Repeated measurement and recording methods
In order to reduce measurement differences, it is recommended to fix the measurement method during acceptance or commissioning and keep complete records. The record content includes: measurement method, instrument model and calibration status, effective air outlet area value, measuring point layout, FFU speed or control setting, filter status, environmental conditions, measurement time and readings.
If data from different FFU or different batches need to be compared, the same method and the same instrument should be used. Aili Industrial will record the air volume and wind speed data during the FFU factory test to facilitate verification by the project party during on-site measurement. If the project usesThe FFU/EFU group control touch screen controller performs speed setting and should also record the control setting values to ensure consistent measurement conditions.
Issues that should be confirmed in advance during project communication
During the FFU acceptance and measurement method confirmation stage, it is recommended to confirm the following with the manufacturer and the acceptance party: whether the air volume hood method or the wind speed conversion method is used for air volume measurement; how to obtain the effective air outlet area for wind speed conversion; the number and arrangement of wind speed measurement points; the air volume hood model and calibration status; the rotation speed or control setting during measurement; filter status and running time; environmental conditions and measurement time; whether repeated measurements and cross-verification are required; measurement record format and judgment standards.
Confirming these issues before acceptance can reduce on-site disputes. For clean room projects, FFU air volume measurement is only part of the acceptance. It also needs to be combined with filter leak detection, wind speed uniformity and room cleanliness to make a comprehensive judgment.
in conclusion
The inconsistency between FFU air volume hood measurement and wind speed conversion is usually not a problem with the equipment itself, but is caused by differences in the effective area, measuring points, hood resistance, or instrument conditions. When troubleshooting, you should first check the method and then judge the equipment performance. Unifying the measurement caliber, fixing the measurement method and keeping complete records are effective ways to reduce measurement differences.
Aili Industrial has complete production capabilities in FFU complete machines and testing, and can record factory air volume and wind speed data to facilitate verification by the project party during on-site acceptance. If you need to know more about the FFU complete machine configuration and test caliber, you can visitAili Industrial FFU fan filter unit。
