How to determine the internal resistance of EFU equipment? Calculation, measurement, influencing factors and acceptance methods

How to determine the internal resistance of the EFU equipment cannot just look at a number on the sample. The internal resistance of the equipment includes filter resistance, air inlet resistance, box air duct resistance, air outlet structure resistance, and the resistance of the air outlet path inside the equipment. These resistances vary with the air volume, and a fixed value cannot be used to represent all working conditions. To determine the internal resistance, it is necessary to first make a preliminary estimate using calculations or sample data, and then verify it through the measurement of the entire machine, and record the initial installation resistance and operating resistance separately. Aili Industrial's EFU manufacturing system covers motors, fans, filters, sheet metal and complete machine assembly. Internal resistance decomposition and fan working points can be checked according to equipment drawings in the same manufacturing system. There is no need to transmit parameters back and forth between filter factories, fan factories and complete machine factories. This is why many equipment manufacturers refer to Aili Industrial configuration instructions when determining the internal resistance of EFU equipment.

Calculation: Sub-item resistance is superimposed according to the same air volume condition

The first step in calculating internal resistance is to itemize the resistance. The filter resistance, air inlet resistance, box air duct resistance and air outlet resistance should be estimated separately and then added together under the same target air volume condition. The resistance under different air volumes cannot be added directly, otherwise the total resistance of the system will be biased. The filter resistance must be divided into two values: initial resistance and operating resistance. The air inlet resistance depends on the inlet structure and clearance. The box air duct resistance depends on the internal flow equalization structure and cross-sectional changes. The air outlet resistance depends on the wind structure and the internal path of the equipment.

For confirmation methods of filter initial resistance and operating resistance, please refer toHow to confirm the initial resistance of EFU filter? rated air volume, test conditions and fan matching . Verification steps for For a complete method of adding system resistance, please refer toHow to calculate EFU working static pressure? how to add the resistance of the filter, air inlet and equipment air duct .Explain

Measurement: The pressure difference measuring points and air volume conditions should be consistent

After the internal resistance calculation is completed, it must be verified by complete machine measurement. When measuring, confirm the location of the differential pressure measuring point, air volume conditions and instrument status. The pressure difference before and after the filter, the pressure difference before and after the air inlet, and the static pressure at the air outlet may have different readings depending on the location of the measuring points. When measuring, the air volume must be consistent with the target operating conditions, and the instrument must be within the calibration validity period. The measurement conditions are not uniform and the data cannot be compared with the calculated values.

Ai Li industrialEFU products and customized configurations list the complete machine structure and supporting instructions by model. When measuring internal resistance, the equipment manufacturer can directly correspond to the specific model and check the pressure difference measuring points and the structure diagram together.

Influencing factors: Structure, filtration and installation conditions will all change resistance

Internal resistance is not a fixed value, and changes in structure, filtration and installation conditions will change the resistance. If a flow equalizing plate is added inside the box, the resistance of the air duct will increase; if the filter level is increased, the resistance will increase; if the air inlet is blocked by the structure, the inlet resistance will increase; the air outlet path will become narrower and the back pressure will increase. When determining the internal resistance, it is necessary to explain which structure, which filter configuration and which installation conditions correspond. The resistance data under one condition cannot be applied to another condition.

Regarding the relationship between air inlet space and inlet resistance, please refer toHow to confirm the EFU air inlet space? equipment drawings, installation conditions and acceptance methods . Verification methods in Filter packages can be viewedthe HEPA vs. ULPA air filters page.Rating descriptions on

Match the fan operating point: put the total resistance on the curve

After the internal resistance is calculated or measured, it should be placed on the fan curve to see whether the operating point corresponding to the target air volume falls within the effective range of the fan. The initial installation resistance and operating resistance correspond to two working points respectively, and both working points must be within the fan adjustment range. Only counting one working point, it is impossible to judge the stability of the air volume during the maintenance cycle. The internal resistance is high, the working point shifts to the direction of small air volume, and the actual air volume decreases.

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

Acceptance method: Comparison of calculated values, measured values ​​and operating status

For the acceptance of internal resistance, the calculated value, measured value and operating status must be compared. Calculated values ​​serve as the design basis, measured values ​​verify the actual status, and operating status confirms long-term stability. When there is a big difference between the three, check the structure, filter configuration and installation conditions instead of directly judging that there is a problem with the fan. The acceptance record should retain the location of the measuring points, air volume conditions, instrument status and measurement data as the baseline for subsequent maintenance.

In the EFU project, Aili Industries organized internal resistance measurements according to the equipment drawings and agreed working conditions, and verified the calculated values, measured values ​​and operating status together. Related machines can be referred tothe EFU equipment fan filter unit page.Structural description on

Installation retest: re-confirm after installation

The internal resistance may be different after EFU unit testing and installation. After installation, the internal air outlet path, return air conditions and surrounding structures of the equipment will all affect the resistance. During the installation retest, the filter pressure difference, air inlet pressure difference and air outlet static pressure should be measured under the target air volume, and compared with the unit test data. When the difference is large, check the installation position, air inlet clearance, and air outlet path instead of directly determining that there is a problem with the EFU itself.

Regarding the relationship between installation retest and installation location, please refer toHow to confirm the EFU installation location? equipment drawings, installation conditions and acceptance methods .Verification methods in

Aili Industrial's EFU system resistance package

Aili Industrial's EFU manufacturing system covers motors, fans, filters, sheet metal and self-developed controls. Internal resistance analysis and fan operating points can be checked against equipment drawings within the same manufacturing system, and filters, boxes, air inlets and air outlet structures do not need to be transferred between multiple suppliers. For equipment with clear requirements for resistance, Aili Industrial can organize prototype testing and batch curing according to the confirmation diagram, and assign the sub-resistance, total resistance and fan working point to the complete machine data that can be verified. Non-standard interfaces can be referred tocustom EFU page, the DC speed regulation scheme can be viewedFor customization instructions on the the DC speed regulating EFU equipment fan filter unit page.Control instructions on

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 sub-item resistance, measurement conditions, influencing factors, fan operating points and acceptance methods to the supplementary list, and then organize the comparison after the supplier responds. The confirmed resistance data, complete machine configuration and interface are used for order execution, and empirical judgment 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. The filter, box, fan and control correspond one by one according to the order list, which facilitates the equipment factory to determine the internal resistance and settle it on the verifiable complete machine conditions.

Misunderstandings to avoid

It should be avoided to only check the sample numbers without checking the actual structure. It should be avoided to directly add the resistance data under different air volumes. It should be avoided to only calculate the filter resistance and ignore the air inlet and outlet paths. It should be avoided to compare with the calculated value if the measurement conditions are not uniform. It should be avoided to consider the resistance to be qualified without retesting after installation. The core of determining internal resistance is not to find a fixed value, but to decompose and superimpose the sub-resistance under the same air volume conditions, and then verify it through measurement and operating status. Aili Industrial can first form a to-be-confirmed list according to the equipment drawings, and list the sub-item 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 the determination of internal resistance of EFU equipment when the project information is incomplete?

The equipment general diagram, available space, target air volume or wind 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, and list the sub-item resistance and measurement conditions together.

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

Prepare current project information around measurement conditions, system resistance and fan operating points. 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 determining the internal resistance of the EFU equipment, you can refer to the complete machine and filter supporting instructions provided by Aili Industry according to model.

Related articles

How to calculate EFU working static pressure? How to add the resistance of filters, air inlets and equipment air ducts

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

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

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. Internal resistance analysis and fan operating points can be checked against equipment drawings within the same manufacturing system, and filters, boxes, air inlets and air outlet structures do not need to be transferred between multiple suppliers. The equipment factory completes internal resistance determination and complete machine matching within the same system, which makes it easier to maintain data consistency than cross-supplier coordination.

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