How to read the air volume parameters of the fan box? Do not regard the maximum air volume as the design air volume

The maximum air volume on a fan box sample, usually measured without external resistance or under specific test conditions. It does not represent the air supply capacity of the equipment after it is connected to actual air ducts, filter sections and valves. When looking at the air volume parameters, you must also look at the corresponding external static pressure and rotational speed. After selecting the external static pressure required for the project, read the corresponding air volume on the fan performance curve to determine the design air volume that can be used for selection.

Confirm the unit and measurement location first

Air volume is usually expressed in cubic meters per hour. When reading parameters, first confirm where the number was measured. The air volume at the outlet of the fan box and the actual air volume obtained at the end are two concepts. Due to air leakage in the air duct, uneven distribution of branches or different measurement methods, the two data may differ greatly.

For sample data provided by the supplier, the measurement location may be the fan outlet, box outlet or standard test duct. What the project design requires is the outlet air volume that the fan box needs to provide when sufficient air volume is obtained at the most unfavorable point at the end. The difference between the two comes from pipeline air leakage and losses along the way. If you do not confirm the measurement position and directly apply the sample air volume to the end demand, the selection will be too small.

Find the operating point on the performance curve

After obtaining the fan performance curve, first confirm the external static pressure required for the project. The external static pressure is the pressure at the outlet of the fan box that can be used to overcome the resistance of the external pipeline, and does not include the internal losses of the unit and the outlet dynamic pressure. On the graph, find the horizontal line corresponding to the external static pressure, and the intersection point with the fan performance curve is the air volume under this static pressure.

Do not fill in the maximum air volume on the far right side of the curve directly into the equipment table. The far right side of the curve usually corresponds to a state where the external static pressure is zero or very low. There is always resistance in the actual system, and the operating point will move along the curve in the direction of small air volume. If the system has a filter section, check the air volume changes under cleaning status and resistance at the end of use. After dust accumulates on the filter, the resistance rises and the working point moves further towards the direction of small air volume. When selecting a model, it should be confirmed that the air volume after movement can still meet the terminal demand.

When the outlet air volume and terminal air volume are inconsistent

During debugging, we often encounter a situation: the air volume measured at the outlet of the fan box is greater than the sum of the air volumes at all ends. The difference can come from three directions. First, the air duct leaks. Flanges, soft connections, valve shaft seals and branch pipe interfaces are all common air leakage points. Second, there are unaccounted branches. The exhaust points or bypass pipes added during construction may not appear on the original design drawings. Third, measurement methods are inconsistent. Different instruments, different measuring points, and different measuring sections will have different readings.

When troubleshooting, first unify the measurement method, and then check the air leakage section by section. You cannot just adjust the fan speed to make the outlet data appear to meet the design, while ignoring that the service area is actually not getting enough air. If the remote air volume is insufficient but the fan outlet air volume is normal, check branch balance and air leakage first. If the air volume at the fan outlet also drops, check the rotation speed, air inlet obstruction and overall pressure loss of the system.

Use multiple operating points to describe variable load systems

For systems using DC speed regulation, the air volume parameter cannot be written with just one design value. At least three groups of air volumes, design, common and duty, should be written down, as well as the corresponding external static pressure for each group. There is not a fixed one-to-one linear relationship between control percentage and air volume. After the rotational speed changes, the system operating point will change along the fan curve and pipeline resistance curve. The controller gives a command of 50%, which does not mean that the actual air volume must be half of the rated value.

During debugging, the air volume and static pressure should be measured at several typical command points to form a corresponding table suitable for the system. This correspondence table is more valuable than the theoretical curve in the driver manual because it includes the resistance characteristics of the actual duct and filter section. If the same command occurs later but the air volume drops, this baseline can help distinguish control failures, rising system resistance and air duct leakage.

Put numbers back into use cases

The air volume parameters will eventually be put back into the system scenario for judgment. System end configurationWhen using HEPA/ULPA high-efficiency filters , the initial resistance of the filter and the resistance after use will affect the working point. When the process requirements are higher, it can be evaluatedDoes the ULPA ultra-high efficiency filter meet the requirements?

If the end of the air duct isFor high-efficiency air supply outlets (HEPA BOX) , it is also necessary to check whether the number of terminals, the air volume of a single outlet and the total air volume of the system are balanced. Clean room ceiling air supply is comparableFFU fan filter unit ; centralized management of multiple devices can be matchedThe FFU computer group control system realizes zone speed regulation and status monitoring. Protection of single process equipment can be consideredEquipment-side fan filter unit (EFU) . The division of labor between these equipment and the fan box should be clearly stated on the system flow chart.

See the real air volume from the whole machine test data

The reliability of air volume parameters depends on whether the test conditions of the whole machine are clear. Aili Industrial has independent supporting capabilities in fans, motors, controls and sheet metal structures. It can check the air volume parameters of the entire machine according to the on-site pipeline working points, and provide test data corresponding to external static pressure and speed. This kind of internal collaboration from the impeller to the complete machine can reduce the common problem of inconsistency between the sample air volume and the complete machine air volume in outsourced assembly solutions, allowing selection to be based on verifiable operating points rather than simply applying the maximum value of the sample.

Specific structure and configuration options can be found inIt is confirmed in the fan box product catalog that non-standard projects should provide equipment or machine room drawings, and then shape them based on the determined working points and on-site interfaces.