When FFU uses wind speed to calculate air volume, which air outlet area should be used?
Multiply the wind speed by the area. If the area is taken incorrectly, the result will be biased.
In FFU air volume calculation, the common method is to measure the average wind speed on the air outlet surface and then multiply it by the effective air outlet area. The formula looks simple, but in actual use, deviations in results often occur, often due to the area value.
The overall dimensions, filter size and actual air supply area of the FFU are not exactly the same. The box has a frame, the filter has a sealing edge, and the air outlet surface may have battens, protective nets or diversion structures. If the air outlet area is directly multiplied by the length and width of the box shape, the calculated air volume will be higher because the frame and non-air supply parts are also taken into account.
Therefore, when converting air volume from wind speed, the effective air outlet area corresponding to the measurement plane and method should be used instead of the box outer area. In the FFU complete machine test and parameter description, Aili Industry will mark the diameter of the air volume, wind speed and effective area to facilitate verification by the project party. For the basic structure of the FFU machine, you can refer toAili Industrial FFU fan filter unit。
The difference between appearance area, filter area and effective air outlet area
The overall area is the length multiplied by the width of the FFU cabinet, usually marked according to the nominal size, such as 1175×575 mm. This size is mainly used for ceiling openings and installation arrangements, and is not equal to the actual air supply area.
The filter area is the nominal size of the filter element and is usually marked according to the nominal size. The filter is installed in the FFU box with a sealing edge or installation frame around it. The actual area of the filter material exposed to the air flow may be smaller than the nominal area of the filter.
The effective air outlet area is the net area through which the airflow actually passes and participates in the air supply. It is usually equal to the net opening area of the filter outlet side, minus the frame, battens, sealing structures and any obstructions. For FFUs with different structures, the effective air outlet area needs to be confirmed according to the actual structure.
When converting air volume from wind speed, the effective air outlet area should be used instead of the external area or the nominal area of the filter.
The measuring plane and area diameter should correspond
The effective air outlet area not only depends on the structure, but also on the measuring plane. If the wind speed is measured close to the air outlet surface of the filter, the effective area is close to the net air outlet area of the filter. If the wind speed is measured at a certain distance from the wind outlet surface, the airflow may have spread or contracted, and the corresponding effective area will change.
Therefore, the area value should correspond to the measurement plane and method. The measurement method describes the location, distance and number of measurement points, and the area value should also be determined based on the same caliber. If the measurement method and area caliber are inconsistent, the conversion results will not be comparable.
For the same FFU, if the measurement plane is changed or the measuring point arrangement is changed, the average wind speed may change, and the corresponding effective area may also need to be adjusted. This is why when different people use the wind speed method to calculate the air volume of the same FFU, the results may be inconsistent.
How to confirm the effective air outlet area
To confirm the effective air outlet area, you can start with the filter and air outlet surface structure. First confirm the actual net air outlet size of the filter, and deduct the portion occupied by the sealing edge and installation frame. Then confirm whether there are battens, protective nets, deflectors or other obstructions on the air outlet surface, which will further reduce the effective area. Then confirm the position of the measurement plane and calculate the effective area according to the corresponding plane.
If the manufacturer provides an effective air outlet area or air volume test report, the manufacturer's data can be used directly. If the manufacturer does not provide it, it can be calculated based on actual structural measurements, or cross-validated with an air volume hood on site.
Aili Industrial will record the air volume and wind speed during the FFU factory test, and mark the test caliber in the parameter description to facilitate verification by the project party under the same conditions. If the project needs to compare FFU air volume data from different manufacturers, it is recommended to confirm whether the area diameters used by both parties are consistent.
A simple accounting example
Assume that the external dimensions of an FFU are 1175×575 mm and the external area is approximately 0.676 square meters. If the net air outlet size of the filter is 1150×550 mm, the effective air outlet area is approximately 0.633 square meters. If the measured average wind speed is 0.45 meters per second, the air volume calculated using the external area is approximately 0.304 cubic meters per second, and the effective air outlet area is calculated to be approximately 0.285 cubic meters per second. The difference between the two is about 6.7%.
If the FFU structure also has battens or protective nets, the effective air outlet area will be further reduced and the difference will be even greater. This example shows that the area value has a significant impact on the air volume calculation results.
In actual projects, the net air outlet area of the filter or the effective air outlet area marked by the manufacturer should be used as the standard, and the measurement method and measuring point location should be recorded.
How to cooperate with other measurement methods
Wind speed conversion is a common method but can also be cross-validated with air volume hood measurements. The air volume hood directly measures the air volume and is not affected by the area value, but the hood itself will increase resistance and change the FFU working point. The combination of the two methods can provide a more comprehensive understanding of the FFU air volume status.
If the project usesThe FFU/EFU group control touch screen controller sets the rotation speed, and the rotation speed or control settings should also be recorded during measurement to ensure that different measurements are performed under the same working conditions.
For projects that require accurate air volume data, it is recommended that the measurement method, area diameter, measurement point arrangement and judgment criteria be specified in the technical agreement. Aili Industrial has complete production capabilities in FFU complete machines and testing, and can provide air volume test data and area diameter specifications according to project needs.
Issues that should be confirmed in advance during project communication
During the FFU air volume calculation and acceptance stage, it is recommended to confirm the following with the manufacturer: how to value the effective air outlet area; measurement plane and measurement point layout; anemometer model and calibration status; rotation speed or control settings during measurement; filter status and operating time; whether an air volume test report is provided; whether cross-validation is required for air volume hood measurement and wind speed conversion; judgment standards and allowable deviations.
Confirming these issues before acceptance can reduce on-site disputes. If you need to know more about the FFU overall machine configuration and air volume parameters, you can visitAili Industrial FFU fan filter unit , you can also contact Aili Industrial to obtain project selection support.
in conclusion
When using wind speed to calculate FFU air volume, the effective air outlet area should be used instead of the box shape area or the filter nominal area. The effective air outlet area needs to deduct the frame, sealing structure, battens and obstructions, and correspond to the measurement plane and method. Depending on the area value, the air volume calculation results will be significantly different.
Aili Industry has complete production capabilities in FFU complete machines and testing, and can mark the air volume, wind speed and area diameter to facilitate verification by the project party under unified conditions. If you are sorting out FFU air volume calculation or acceptance methods, you can visitAili Industrial FFU fan filter unit understands the complete machine configuration. You are also welcome to contact Aili Industrial for project selection support.
