AC Centrifugal Fan for Fan Filter Units: 1854 m3/h Case Study

What the FFU builder needed

An OEM building a new fan filter unit needed an AC centrifugal fan reaching about 1800 m3/h. They asked for a backward-curved 315mm impeller on a simple AC motor.

The call for three separate levels is what shapes the project. Roughly 1800, 1600 and 1400 m3/h, which points straight at a three-speed motor.

That pattern usually means two working modes plus a margin. Namely a high-power purge cycle, and a quieter standard mode.

• 220V single phase at 50Hz, because cleanroom kit there runs on it.
• Three fixed speeds from the AC centrifugal fan, rather than smooth modulation.
• Enough static pressure to force air through HEPA or ULPA media.
• CE certification, plus compliance with EN 60335-1.
• Lastly, a bare motorised impeller, so it drops into their own chassis.

Here the customer never named a pressure figure. Experience fills that gap. An FFU this size needs 250 to 350 Pa, since a HEPA filter is basically a wall the fan must push through.

Specifying the AC centrifugal fan

The brief named an AC motor. Therefore the first question was whether to argue with it.

Whether to propose EC instead

An EC fan from our SmartEC platform offers better efficiency and fully variable speed. We weighed it, then decided against.

Basically the reason is what the customer really needs. Three fixed speeds, rather than smooth modulation. A three-speed capacitor-run motor does that directly, and at lower cost. In the FFU market, cost is often what decides. Consequently following the brief was the shortest route to both their goals.

The model that fitted

So we chose the existing LWFU-AC315S-01, built for exactly this job. Its tapped-winding motor gives 1300, 1050 and 850 RPM. Those three speeds land on the airflow points the customer named.

Why backward-curved, and why aluminum

A 315mm backward-curved wheel builds static pressure well, which is just what a filter bank demands. A forward-curved wheel moves more air at low resistance. Here, however, it would struggle.

Aluminum alloy keeps the spinning mass low. Consequently start-up current falls, and so does bearing wear across the 20,000-hour L10 design life.

Meanwhile the -30C to +60C range follows from parts chosen under our ThermoFlex principles. In the end the assembly gives up to 1854 m3/h and 335 Pa from a 220V supply, matching the enquiry exactly.

Technical Specifications

Meanwhile the table lists three speeds, each with its own airflow and pressure. Read them as three separate duty points, not one AC centrifugal fan with a dial.

Technical Documentation

The following documents were provided to the customer to support their design and procurement process.

LWFU-AC315S-01 Technical Datasheet (PDF)
The PDF contains the complete technical datasheet, including performance curves, dimensional drawings, and electrical specifications, essential for design engineers and system integrators.

Here the image shows the assembled AC motor and 315mm backward-curved impeller, providing a clear visual reference for procurement managers confirming product form factor.

Technical Specification Source File (DOCX)
This Word document provides the source file for the technical specifications, allowing OEM engineering teams to easily copy and paste data into their internal documentation or compliance files.

Why a standard part won

For an OEM in a cost-driven market, four things counted.

• A standard part, priced accordingly. The LWFU-AC315S-01 AC centrifugal fan is already engineered, so this was a documents and quotation project rather than a development one. No development cost arose, and none was charged.
• Certification already held. The assembly is CE certified and designed against EN 60335-1 and ISO 5801. Consequently the OEM own approval work shortens, since the air-moving part is a known quantity.
• Curves, not estimates. We supplied a full datasheet with P-Q curves verified in our lab to AMCA 210/211 and ISO 5801 methods. Consequently we confirm the three duty points before installation, not after.
• Supply that holds up at volume. Nobody builds FFUs one at a time, so stability matters. Quoting and shipping proven off-the-shelf models from our Ningbo base gives a dependable source for a critical component.

Browse our backward-curved centrifugal fan range, or the cleanroom FFU section. ISO 14644 sets out the cleanroom classifications.

Questions FFU builders ask

What is the lead time on 500 units?

Orders of 500 units run 15 to 30 days from confirmation, measured to readiness at our Ningbo factory gate. We coordinate with your preferred freight forwarder for sea or air shipment from there.

Can I use a VFD for finer speed control?

No. This AC centrifugal fan runs a three-speed capacitor motor, which no VFD should drive. Where you genuinely need variable speed, take the equivalent SmartEC model instead. Its integrated EC motor accepts 0-10V or PWM directly, and it includes protections a VFD can interfere with on a standard AC motor.

Is the -30C to +60C range substantiated by testing?

Yes. We validate that range under our ThermoFlex design protocol. Batch samples go through accelerated L10 life testing at +60C to confirm the 20,000-hour design life, and we run cold start and performance checks too. Specific reports are available to customers with active projects.

Why does an FFU need backward-curved blades?

Because filter media resists heavily, and that resistance grows as the filter loads. Backward-curved blades hold their efficiency as pressure climbs, and their power draw peaks rather than running away. A forward-curved wheel does the opposite. Consequently it belongs in low-pressure work instead.