Why is the actual air volume of the EFU lower than the rated value? System resistance, filter and installation condition analysis

The actual air volume of the EFU is lower than the rated value, which is a common problem during the equipment debugging and acceptance stage. The rated air volume is the air supply capacity of the EFU under agreed test conditions. The actual air volume after installation is affected by system resistance, filter status, installation conditions and measurement methods, and is often lower than the sample rating. When purchasing, when you see that the actual air volume is low, it is easy to first doubt the fan's ability. However, the real reason may be filter resistance, air inlet obstruction, box air duct, air outlet structure or measurement diameter. Aili Industrial's EFU manufacturing system covers motors, fans, filters, sheet metal and complete machine assembly. The actual air volume, system resistance and fan working point can be checked according to the equipment drawings within the same manufacturing system. There is no need to confirm back and forth between the fan factory, filter factory and complete machine factory. This is why many equipment manufacturers will refer to the Aili Industrial configuration instructions when analyzing that the actual air volume of the EFU is lower than the rated value.

First distinguish between rated air volume and installed air volume

The rated air volume is the data of the EFU under agreed test conditions, usually marked under specific filter status, external static pressure and rotational speed. The installed air volume is the air supply volume after the EFU is installed on the equipment and connected to the actual air duct and filter. The two test conditions are different, and it is normal for the values ​​to be different. To determine whether the actual air volume is qualified, you must first align the test conditions of the rated air volume with the installed conditions, rather than directly comparing the sample numbers.

For the calculation and unit conversion of air volume, please refer toHow to calculate EFU rated air volume? The method in the air supply area, target wind speed and unit conversion method compares the rated value and installed value under the same caliber.

System resistance: In addition to the filter, there are air inlet and outlet

System resistance is the main reason for the decrease in actual air volume. The system resistance of EFU not only comes from the filter, but also includes the resistance of the air inlet, the resistance of the air duct inside the box and the resistance of the air outlet structure. The air inlet is blocked by the structure and the inlet resistance increases; the flow equalization structure inside the box is unreasonable and the air flow is turbulent; the air outlet path is narrow or blocked and the back pressure increases. After these resistances are superimposed, the fan operating point moves in the direction of small air volume, and the actual air volume decreases.

Ai Li industrialEFU products and customized configurations list the complete machine structure and supporting instructions by model. When checking the system resistance, the equipment manufacturer can directly correspond to the specific model and put the resistance of the filter, air inlet and air outlet structure in the same table for analysis.

Filter status: Dust accumulation and sealing will affect air flow

Filters are an important source of system resistance, but two situations need to be distinguished. The filter accumulates dust, the resistance rises, and the air volume decreases. This is a gradual change in normal operation; the filter seal fails and unfiltered air bypasses. The overall air volume may appear to be normal, but the effective filtered air volume decreases. The former looks at the pressure difference data, and the latter looks at the sealing status. When checking that the actual air volume is low, you must also confirm the filter pressure difference and sealing status, and not just look at the air volume number.

Regarding the relationship between the initial resistance and operating resistance of the filter, please refer toHow to confirm the initial resistance of EFU filter? rated air volume, test conditions and fan matching . Verification method for Filter packages can be viewedthe HEPA vs. ULPA air filters page.Rating descriptions on

Installation conditions: Air inlet clearance and air outlet direction are critical

The impact of installation conditions on actual air volume is often underestimated. The EFU is installed inside the device. If the air inlet is blocked by structures, cables or other components, the inlet resistance will increase and the air volume will decrease. If the air outlet direction deviates from the target area or is blocked by the structure, the effective air supply volume will also decrease. When confirming the installation location, check the air inlet clearance, air outlet path and distance between adjacent units, rather than just whether the EFU can be installed.

For the relationship between the installation position and the air inlet space, please refer toHow to confirm the EFU installation location? Equipment drawings, installation conditions and acceptance methods andHow to confirm the EFU air inlet space? equipment drawings, installation conditions and acceptance methods .Verification methods in

Fan operating point: The operating point will shift after the resistance changes.

The fan operating point is determined by the fan curve and the system resistance curve. The system resistance increases, the operating point moves along the fan curve in the direction of small air volume, and the actual air volume decreases. This is not a fault of the fan itself, but a change in the operating point. To determine whether the actual air volume is reasonable, the system resistance after installation should be placed on the fan curve to see whether the operating point falls within the expected range. If the working point deviates too much, it means that the fan selection or system resistance does not match the design.

Regarding the relationship between the fan working point and the matching of the whole machine, please refer toHow to choose EFU centrifugal fan? working point, power, temperature rise and continuous operation requirements . Checking methods for For projects that require DC speed regulation solutions, please refer toSpeed the DC speed adjustment EFU equipment fan filter unit page.​​adjustment instructions on

Measurement method: Measuring points, instruments and working conditions can also cause deviations

The actual air volume is low. Sometimes it is not an equipment problem, but a measurement method problem. The measurement point is incorrectly located, the instrument is not calibrated, the filter status during measurement is inconsistent with the acceptance conditions, and uneven wind speed distribution causes single-point measurement deviations, which may cause the air volume reading to be low. When troubleshooting, you must first confirm the measurement method, and then determine whether there is a problem with the equipment itself.

For information on surface wind speed measurement and uniformity evaluation, please refer toHow to calculate EFU surface wind speed? How to determine the effective filtration area and average wind speed ?How to evaluate EFU wind speed uniformity? measuring points, averages, deviations and acceptance methods .Measurement methods in

Treatment and retest: locate the cause first and then adjust

When the actual air volume is low, the handling method should correspond to the reason. If the air inlet is blocked, adjust the installation position or clean the clearance; if the filter is dusty, replace it according to the pressure difference; if the seal fails, check the pressure frame and frame; if the fan speed is insufficient, check the control instructions; if there is a deviation in the measurement method, retest according to the same caliber. After processing, it is necessary to return to the original working condition and re-measure the air volume, pressure difference, power and vibration to confirm that the status of the whole machine has returned to the normal range, and update the maintenance records.

Aili Industrial organizes maintenance and retesting according to equipment models in the EFU project, and maps fault symptoms, processing methods and retesting data to the complete machine configuration. Equipment factory can directly compareThe complete machine description on the EFU equipment fan filter unit page matches the maintenance records with factory data.

Aili Industrial's EFU manufacturing system

Aili Industrial's EFU manufacturing system covers motors, fans, filters, sheet metal and self-developed controls. When analyzing actual air volume, filter status, fan operating points and installation conditions can be checked within the same manufacturing system, eliminating the need to confirm responsibilities among multiple suppliers. For equipment with clear requirements for air volume, Aili Industrial can organize prototype testing and batch curing according to the equipment drawings, and put the rated air volume, installed air volume and system resistance into verifiable complete machine data. Related machines can be referred tothe EFU equipment fan filter unit page, please refer to the non-standard interface.For the structural description on Customize EFU page.Customization instructions in the

How to form executable confirmation results

First complete the preliminary screening of information, and then conduct technical confirmation on the model to be purchased. Add the rated air volume, system resistance, filter status, installation conditions and measurement methods to the supplementary list, and then organize the comparison after the supplier responds. The confirmed air volume, resistance and complete machine configuration are used for order execution, and sample ratings cannot be used to replace the data of this project. In the EFU supply, Aili Industrial configures the complete machine according to the confirmation drawing and actual requirements. Fans, filters, cabinets and controls correspond one by one according to the order list, which facilitates the equipment factory to analyze the actual air volume and settle it on the verifiable complete machine conditions.

Misunderstandings to avoid

You should avoid directly comparing the rated air volume of the sample with the installed air volume. You should avoid only doubting the fan and ignoring the system resistance and installation conditions. You should avoid looking at the air volume without looking at the pressure difference and sealing status. You should avoid judging the equipment as unqualified if the measurement method is not uniform. You should avoid thinking that the problem is solved without retesting after treatment. If the actual air volume is lower than the rated value, it may be a problem with the system resistance, filter, installation conditions, fan operating point or measurement method. The scope of troubleshooting must be narrowed down step by step. Aili Industrial can first form a to-be-confirmed list according to the equipment drawings, listing the air volume, resistance and measurement conditions together.

Related questions and answers

Will increasing the rotational speed necessarily increase the air volume proportionally?

uncertain. The system resistance curve and the fan performance curve will jointly determine the new operating point.

How to promote EFU actual air volume analysis when the project information is incomplete?

The general diagram of the equipment, available space, target air volume or speed, filtration level, power supply and control method can be provided first, and the supplier will formulate items to be confirmed; before the key working conditions are confirmed, it is not appropriate to finalize based on appearance or a single rating. Aili Industrial can first form a to-be-confirmed list according to the equipment drawings, listing the air volume, resistance and measurement conditions together.

What specific information do I need to prepare for this question?

Prepare current project information around filtration efficiency, resistance, sealing and leak detection. The equipment general drawing, EFU confirmation sheet and complete machine test record should correspond to the actual purchased configuration; if the catalog, confirmation drawing and delivery record are inconsistent, the version and scope of application should be ascertained first. When analyzing that the actual air volume of the EFU is lower than the rated value, you can refer to the complete machine and filter supporting instructions provided by Aili Industry by model.

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What is the reason for the decrease in EFU air volume? Inspection sequence, processing methods and preventive measures

How to confirm the initial resistance of EFU filter? Rated air volume, test conditions and fan match

How to calculate EFU surface wind speed? How to determine the effective filter area and average wind speed

Key points for selection and acceptance inspection

Aili Industrial EFU selection and procurement support

Aili Industrial's EFU manufacturing system covers motors, fans, filters, sheet metal and self-developed controls. When analyzing actual air volume, filter status, fan operating points and installation conditions can be checked within the same manufacturing system, eliminating the need to confirm responsibilities among multiple suppliers. The equipment factory completes complete machine analysis and maintenance within the same system, making it easier to find the root cause of the problem than cross-supplier coordination.

learnAili Industrial EFU products and customized configurations , the complete machine structure can be viewedEFU equipment fan filter unit , the control scheme can be viewedDC speed regulating EFU equipment fan filter unit , filter package can be viewedHEPA and ULPA air filters . Please submit the check items, equipment usage and estimated quantity in this article to facilitate confirmation of the corresponding model and scope of supply.