An EC plug fan can be a useful way to move air through an air handling unit (AHU), but the wheel alone does not define the result. Filters, coils, inlet clearance, discharge space and control settings all affect the installed duty. Before choosing a fan, define the required airflow and the pressure boundary at which it must be delivered. Then check the exact fan configuration against that duty and the available cabinet space.
The video shows the basic construction and airflow path. Use it to understand the arrangement; use the selected model’s current drawing, curve and wiring document to approve an actual installation.
What a plug fan actually includes
A plug fan has an open backward-curved wheel rather than a scroll casing around its discharge. The motor and wheel are supported by a mounting arrangement, and the assembly discharges into an AHU plenum. That construction can make an array practical, but it also makes the surrounding cabinet part of the airflow design. A nearby wall, poor inlet approach or obstructed discharge can change the result from the free-field fan curve.
The LONGWELL family photograph below identifies visible parts: the inlet ring, wheel, motor-side assembly and support frame. It is a family illustration, not evidence that this specific unit was tested in the AHU shown in the video. LONGWELL’s product documentation distinguishes an unbracketed motorized impeller, a bracketed version, a floor-mounted plenum configuration and a FanGrid module. Their mounting arrangements are not interchangeable merely because each uses a backward-curved EC wheel.
Why the AHU plenum matters
Air passes through the AHU’s filter and coil sections before or after the fan according to the cabinet layout. The fan raises the pressure needed to move the required flow through that path. Its discharge then enters a plenum, where the next section and any nearby obstruction affect distribution. There is no universal cabinet-depth saving from removing a scroll: the usable space depends on the original layout, service access and the new fan’s mounting envelope.
The drawing is a sequence for checking an installation. It does not show a measured LONGWELL result or prescribe one fixed order for every AHU. When reviewing an existing unit, mark the actual filter, coil, fan, damper and discharge locations on a cabinet section drawing. Record the inlet approach and access path as carefully as the overall dimensions.
Select at the required duty point
Start with the required supply airflow, the pressure definition and the operating states the AHU must meet. Keep the filter condition, coil condition and damper position with each pressure reading. A headline maximum airflow is not a selection point because it says nothing about the resistance at that flow. Plot the required duty on the exact candidate’s current fan curve and check the acceptable operating range, electrical input and control response.
LONGWELL’s AHU plug-fan family and EC plug-fan family help identify candidate constructions. A family page or photo cannot establish a particular suffix’s curve, efficiency, electrical interface or cabinet fit. Ask for the full model and revision of its drawing, curve and wiring information before comparing proposals. A change in motor, impeller or support configuration can change what those documents cover.
Check controls, power and service access
An EC motor can provide speed control, but the available command and feedback functions depend on the ordered configuration. List the building management system’s required command, status and fault points. Confirm the exact fan’s supply, protection, earthing and wiring instructions; for a multi-fan cabinet, review combined electrical loading and protective-device behavior. Do not assume a generic interface list applies to every suffix.
Design a path for inspection and removal of the wheel and motor assembly. Check access doors, clearances and any downstream component that may be exposed to a concentrated discharge. These details are especially important in a retrofit, where the original fan base and cabinet structure may not match the new support frame. During commissioning, measure delivered airflow and record pressure and input power at defined states. Fan speed alone is not an airflow measurement.
When an array is worth considering
Several plug fans can share an AHU plenum, so an array may be considered where duty, access or operational continuity justify it. The choice still needs a cabinet-level design. Define how the fans are sequenced, what happens if one stops, and whether the remaining units can safely serve the required reduced duty. Do not assume that an array automatically gives a fixed percentage of backup capacity or a particular energy saving.
Compare a single-fan option and an array at the same required airflow, pressure boundary and operating schedule. Include the frames, controls, wiring, access and maintenance arrangements in the comparison. If the installation demands a direct duct connection or a different airstream construction, examine a housed fan or another suitable design rather than forcing a plug-fan layout into the space.
A review package an engineer can verify
A useful request for quotation includes the AHU section drawing, required airflow, pressure reference points, operating states, available supply and control interface, access envelope and any relevant environmental limits. For each candidate, keep the full model suffix and current curve, drawing and wiring document together. Record which claims are product data and which depend on the completed AHU design.
That approach makes the plug fan’s real advantage clear: a flexible construction that can be evaluated against a defined system. It does not promise a universal efficiency, lifetime, cabinet saving or application fit. The final decision belongs to the measured duty and the documented configuration.
Need an AHU fan shortlist? Send the airflow, pressure definition and cabinet section to sales@longwellfans.com.
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