With a Tight Noise Budget, Blade Shape Beats Motor Choice

What the HVAC OEM needed

A European HVAC OEM wanted a direct-replacement cross-flow fan delivering 360 m3/h at 51 dB(A). With a cap that tight, blade shape and noise decide the answer.

They supplied a list of target figures rather than a description. That pattern means one thing. Namely, they are qualifying an alternative to a European supplier, probably to cut cost and shorten lead times.

Meanwhile the application is a trench heater or an air curtain, where the point is a wide, even sheet of slow air.

• A total length of 446mm, since the mounting holes sit 365mm apart.
• 230V at 50Hz, because that is the standard European supply.
• 360 m3/h against 36 Pa of static pressure.
• No more than 51 dB(A), since these run in occupied commercial spaces.
• Lastly, a range from -30C to +60C, plus CE marking.

Those dimensions are not guidance. A drop-in either fits the existing chassis exactly, or it is not a replacement at all. Furthermore, 51 dB(A) is demanding alongside that airflow.

Matching the AC cross-flow fan

The brief specified an AC motor. Usually that is the right choice for cost-driven, high-volume HVAC appliances, where simple on/off control does the job.

Confirming the AC choice

Even so, we checked that decision before accepting it. An EC variant from our SmartEC platform would give variable speed and better efficiency.

However, it would also require the customer to change their control system. For a second-source exercise aimed at cost, that defeats the purpose entirely. The AC solution suits their existing manufacturing process, which is what they actually asked for.

Blade shape and noise, in that order

Here the real challenge was hitting the performance inside the size and the noise limits at once.

The model number gives the geometry. Namely an 80mm impeller, 350mm long. That pairing makes the target airflow across the 446mm width of the unit.

Afterwards we optimized blade profile and blade count through simulation. The aim was 360 m3/h at 36 Pa while holding turbulence down, since turbulence is where fan noise mostly comes from.

That is the point worth taking away. At this duty the impeller shape does the acoustic work, rather than the motor. Consequently the result meets 51 dB(A).

Materials, life, and blade shape and noise

Meanwhile the impeller is light aluminum, picked for low spinning mass and rust resistance. Meanwhile the frame is cold-rolled steel, giving the rigidity a 446mm span needs once bolted into a chassis.

High-performance ball bearings give the 30,000-hour L10 life. Equally, they are what makes the -30C to +60C range achievable, following the same thinking behind our ThermoFlex components.

Technical Specifications

The three length dimensions below decide whether this AC cross-flow fan drops in. Read those before the performance rows.

Technical Documentation

Here the initial customer requirement specified key performance metrics, including airflow, pressure, and dimensions, indicating the need for a direct-fit replacement part.

The final approved specification sheet, LWCA-80350SN-06-00, contains all nominal data, technical features, and mechanical drawings required by an OEM design engineer for system integration.

Open LWCA-80350SN-06 Specification Sheet (PDF)

Judging blade shape and noise yourself

Beyond the specification itself, two things carried this.

• Blade shape and noise, answered straight away. A request for a specification sheet went from enquiry through engineering approval to filing very quickly. The same responsiveness extends to a full 90-day custom NPI cycle, against the 12 to 18 months imported European brands quote.
• An equivalent fan, not a cheaper one. This model matches the incumbent mechanically and aerodynamically, which is what makes it a substitution rather than a downgrade. For an OEM competing on price, that distinction is the whole point.

Browse our cross-flow fan range, the AC cross-flow fan series, or the air curtain section. Test methods are defined in ISO 5801.

Questions before you specify one

Does blade shape really matter more than the motor for noise?

At a fixed duty point, usually yes. The motor contributes electromagnetic and bearing noise, which sits well below what the impeller generates aerodynamically. Blade shape and noise are tied together through turbulence and blade passing frequency, and that is where the audible energy comes from.

What are the lead time and MOQ?

A standard make-to-order fan like this runs 15 to 25 days after order confirmation. MOQ generally sits between 100 and 500 units, depending on the production schedule. We also hold stock on certain high-volume models for 1 to 5 day delivery.

Can it run on 60 Hz?

Not as it stands. This model is wound for 50 Hz, and running it at 60 Hz raises synchronous speed by 20%, from 1350 to roughly 1620 RPM. Airflow, power draw and noise all rise with it, and the CE certification no longer applies. For 60 Hz markets we build a version wound for 115V or 230V at 60 Hz through our standard NPI process.

Is it suitable for outdoor units?

Yes, within its rating. The -30C to +60C range, supported by high-quality ball bearings and durable materials, suits equipment in unconditioned spaces or places with wide temperature swings. That window is broader than many standard commercial fans offer.

Why does turbulence matter more than speed for noise here?

Because at 1350 RPM the tip speed is already modest, so broad turbulent noise dominates rather than a blade-passing tone. Turbulence comes from how air leaves the blades and meets the housing. Consequently blade profile is the lever you pull. Slowing the fan further would cost airflow with little acoustic gain.