EC Plug Fan for Compact AHU: 1730 m3/h Case Study

What the AHU builder needed

An OEM was developing a new range of compact air handling units and needed an EC plug fan capable of 1,730 m3/h at peak. Just as importantly, it had to reach 525 Pa of maximum static pressure.

That pressure figure comes from what is inside the unit. A dense cooling coil and high-efficiency particulate filters together create a lot of system impedance, so the real duty point was 1,200 m3/h against 350 Pa.

The rest of the brief was tight in every direction.

• A mounting footprint under 300 by 300mm, since the cabinet was already fixed.
• 230 VAC at 50 or 60Hz, for European and comparable grids.
• An EC motor with 0-10V speed control, for the customer BMS and for ASHRAE 90.1 efficiency targets.
• Reliable running anywhere between -25C and +60C.
• CE marking, plus ETL to UL 507 for a planned North American version.
• Finally, no more than 74 dB(A) at free-air delivery.

When pressure rather than volume is the binding constraint, most of the fan world is eliminated before you start. That is exactly what happened here.

Selecting the EC plug fan

Here the first decision took almost no time. Basically, an axial fan cannot do this job.

Why not axial

Axial fans move large volumes of air very efficiently at low pressure. Ask one to push through 350 Pa of coil and filter resistance, however, and it simply stalls. So the answer had to be centrifugal.

Backward-curved rather than forward-curved

A forward-curved wheel was considered briefly. Backward-curved won for two reasons.

Firstly, backward-curved impellers reach higher static efficiency, which matters when the fan runs continuously. Secondly, they have a non-overloading power characteristic. In other words, the motor power peaks and then falls rather than climbing indefinitely as system resistance drops. In a variable-speed AHU where filters load up and resistance shifts over time, that behavior is worth having.

Why the drive is built in

An AC motor with an external VFD would have worked electrically. It would also have forced the customer to source, mount, wire and warrant a separate drive.

An integrated EC plug fan removes all of that. It is more efficient at part load, which is where an AHU spends nearly all its life, and the control wiring is a single 0-10V input.

The selected fan

The specified model is the LWBE3G250-092PS-20. It is a 250mm backward-curved EC plug fan with the motor integrated.

Plug configuration means there is no scroll housing, so the fan mounts straight onto a plenum wall inside the unit. That saves depth, and it removes the pressure losses a scroll would add.

Its SmartEC drive electronics provide the 0-10V and PWM interface for BMS integration. Meanwhile the -25C to +60C range comes from our ThermoFlex approach to motor components and heat paths.

Technical Specifications

Read the maximum static pressure row against the duty point above. The margin between them is what gives an AHU designer room to add a filter later. In an EC plug fan, that margin is the whole point.

Technical Documentation

Meanwhile the complete technical datasheet for the LWBE3G250-092PS-20 EC backward centrifugal fan, containing performance curves, dimensional drawings, and electrical specifications for review by design engineers. Download Datasheet.

A product image of the LWBE3G250-092PS-20 plug fan, showing the motor, backward-curved impeller, and mounting bracket for visual confirmation by procurement managers and system integrators.

Why the OEM sourced from us

The OEM was rebuilding an AHU platform under bill-of-materials pressure. Two things settled the choice.

• Performance the customer verified themselves. Aerodynamic performance and EC motor efficiency were validated in the customer own lab rather than accepted from our datasheet. That is the right way round, and we would rather be checked than believed.
• Curves you can simulate against. All our fan data, the LWBE3G250 P-Q curve included, is tested to AMCA 210/211 and ISO 5801 methods in an independently verified lab. Consequently the designer does not need to de-rate defensively.

Browse our EC plug fan range, or the AHU fan section for larger units. Energy targets are set out by ASHRAE in Standard 90.1.

Questions from the controls engineer

What L10 life should I expect at 50C rather than 40C?

Here the published 40,000 hours is referenced at 40C. At a continuous 50C, a standard derating applies and you would typically see 25,000 to 30,000 hours. Send us your actual duty cycle and load and we will calculate it properly. The fan also carries over-temperature protection for the windings and electronics.

Can I read fan speed back through the 0-10V line?

No, that line is a one-way input for setting speed. Use the dedicated tachometer output instead, which gives one pulse per revolution as an open-collector signal. There is also an auxiliary +10VDC supply on the harness to power the pull-up resistor, which simplifies most controller wiring.

Can these be used in a FanWall or FanGrid array?

Yes. This EC plug fan is often used singly in smaller units, though the LWBE3G platform is designed for arrays. Its stable pressure curve and integrated controls suit parallel operation, and a 2×2 array of 250mm fans delivers up to 3,460 m3/h. For larger arrays we help with spacing and a master control strategy over Modbus RTU.

Why does a plug fan suit a compact AHU?

Because the scroll housing is what makes a conventional centrifugal fan bulky, and inside a plenum it is redundant anyway. Removing it shortens the assembly, simplifies the airflow path into the coil, and gives you back the pressure the housing would have consumed.