AC Centrifugal Fan for AHU and RTU: 3151 m3/h Case Study

What the AHU builder needed

An HVAC OEM building a new line of air handling units needed an AC centrifugal fan reaching 3,151 m3/h. The brief merely asked for a spec sheet matching that figure.

A short brief still tells you something. Namely, they want a standard AC centrifugal fan for a tight market, not a development project.

Meanwhile the housing was the real limit. It already existed, being 341mm wide and 328mm tall.

• 220 VAC at 60Hz, since that is the mains supply there.
• Roughly 250 Pa of system pressure, since filter banks and coils both resist.
• No more than 65 dB(A), because commercial buildings set acoustic limits.
• CE certification as mandatory, plus EN 60335-1 adherence strongly preferred.
• Lastly, S1 continuous duty with an L10 life of at least 50,000 hours.

That last line is about warranty rather than physics. An OEM shipping thousands of AHUs cares less about any one fan than about how many come back.

Fitting the AC centrifugal fan to the housing

Three decisions shaped the answer. Namely motor type, impeller type, and inlet layout.

AC rather than EC

Certainly an EC motor is more efficient, and it offers variable speed. However, this AHU is cost-driven and runs at fixed airflow.

So an AC induction motor avoided both the cost of an EC drive and the fuss of an external VFD. Neither is needed here, which matched their unstated wish for a proven, plain component.

Forward-curved rather than backward-curved

Admittedly a backward-curved wheel reaches higher pressure. Under 500 Pa, though, the system sits squarely in forward-curved territory.

A forward-curved multi-blade wheel delivers more airflow for its diameter, which is exactly what a tight housing rewards.

Why double inlet was essential

Ultimately this is the choice that made the housing work. Reaching 3,151 m3/h inside 341 by 328mm needs a double-inlet, double-width layout, marked DS in the model number.

Drawing air from both sides nearly doubles the airflow capacity of a given wheel diameter. Consequently the fan gets its performance from width rather than from diameter, and the axial length shortens instead of growing.

The specified fan

Finally we proposed the LWFA4E225-138DS-03-00. It pairs a 225mm galvanized steel forward-curved wheel with a 138mm external rotor motor.

Direct drive removes belts and pulleys, which takes service points out of the finished AHU. Meanwhile at 60Hz the fan gives 3,151 m3/h and 494 Pa peak pressure, with Class F insulation and IP54 protection.

Technical Specifications

Two frequency columns appear below. The 60Hz one applies to this project, and the gap between them is worth noting on any AC centrifugal fan.

Technical Documentation

The following documents were generated and approved during the project lifecycle, culminating in the final deliverable to the customer.

LWFA4E225-138DS-03-00 Technical Datasheet (PDF)
The full technical datasheet provides performance curves, dimensional drawings, and certification details for engineering review and system integration.

Here the product image shows the double-inlet forward-curved centrifugal fan with its integrated external rotor AC motor.

LWFA4E225-138DS-03-00 Specification Sheet (DOCX)
The editable specification sheet can be used by procurement teams to integrate product data into their internal systems and documentation.

Why the OEM specified our fan

Beyond the specification, three things counted.

• European performance, lower price. This AC centrifugal fan matched established European models on output, yet landed materially below them on price. In a cost-driven AHU market, that gap is a real advantage.
• Lead times measured in days. As a standard inventoried model it ships on a 15 to 25 day make-to-order lead time, against the 12 to 18 weeks imported European brands commonly quote. That lets an OEM finalise its design and start production far sooner.
• Documentation that removes a step. Every AC centrifugal fan here is CE marked, with performance verified to ISO 5801. Consequently the OEM engineers design it in without paying for third-party validation before market entry.

Browse our forward-curved centrifugal fan range, or the AHU fan section. Appliance safety comes from IEC 60335-1.

Questions AHU designers ask

What L10 life and bearings does it use?

We calculate 50,000 hours L10 at a 25C ambient, on maintenance-free deep groove ball bearings. Those suit continuous S1 duty in commercial HVAC without any periodic lubrication across the service life.

Is the speed controllable?

Not natively. As an AC induction motor its speed follows line frequency, giving 1250 RPM at 50Hz and 1280 RPM at 60Hz. For variable airflow, OEMs either add an external VFD or take an equivalent SmartEC model with 0-10V and PWM control built in.

What certifications does it carry for Europe?

Full CE marking, confirming compliance with the Low Voltage Directive and the EMC Directive. It is also designed and tested to EN 60335-1, which AHUs in commercial buildings commonly require, and it is RoHS and REACH compliant.

Why does a double-inlet fan fit better than a bigger single-inlet one?

Because airflow scales with the area air can enter through, not with diameter alone. Feeding a wider wheel from both sides raises capacity without growing the diameter. Consequently the fan expands along an axis the housing usually has to spare, rather than one it does not.