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Making a RadiCal Change – Delivering Quieter Enhanced Efficiency

When the application needs airflow and there is resistance to delivering the air through to the point it is required, choosing a backward curved motorised impeller can maximise operational efficiency whilst minimising noise and energy use. The design of the RadiCal backward curved fan range enhances system efficiency further by delivering air using less power more quietly.

In a previous article, I explained why a backward curved motorised impeller should be chosen when the required duty point falls in the area of medium system pressure versus medium volume flow on the fan.

See -

A backward curved fan should be selected within its optimum range which is in the centre of its flow characteristic and this coincides with the point of peak efficiency and quietest operating point.

Air on the inlet side of the impeller should be kept as smooth and laminar as possible by using an inlet ring (Inlet nozzle) overlapping the impeller inlet cone. Using an inlet cone reduces turbulence-induced noise, keeps the power consumption at the duty point to a minimum and maximise efficiency.

A non-overloading characteristic, the ability to install the fan with or without a scroll and an impeller design that provides the highest static efficiency of all types of fans means that the backward curved fan is a flexible, adaptable fan design can be used across a wide range of installations.

Making the Best Better

Backward curved motorised impellers have been around for many years and the performance characteristic of the fans can be manipulated by changing their design attributes. The number of impeller blades used, their size, their profile, their shape, the angle at which they are placed are all attributes that can be adjusted to change performance. Similarly, the shape of the inlet ring and impeller inlet cone influence the efficiency of how the impeller imparts mechanical energy as the air is drawn through the fan. The equipment designer then needs to consider how the fan is installed ensuring that obstructions or restrictions in the flow path do not add unnecessary turbulence.

Looking at the fan through the eyes of Computational Fluid Dynamics (CFD), enabled ebm-papst to visualise the flow of air through a backward curved motorised impeller. The simulation of airflow through the impeller highlighted areas of high velocity, dead areas and areas where turbulent flow patterns were forming.

Of specific initial interest were the areas above the rotor head, the sharp drop in profile at the edge of the rotor, a dead area on the impeller backplate next to the rotor and rotating turbulence at the impeller outlet.

In addition to these points, the interface between the inlet ring and impeller inlet cone showed a high velocity where some of the higher-pressure exhaust side air was recirculating back through the impeller.

With any mass or fluid medium, sharp changes in direction create a disturbance which in the case of fluid flow results in undesired eddy currents or turbulence. Gradual changes of direction minimise stress within the air path and can maintain homogenous flow as it passes through the impeller.

In addition to removing the dead areas where turbulence can form the interface between inlet ring and impeller inlet cone has been lengthened to minimise recirculation from the exhaust side back into the suction flow path. One final enhancement was added at the impeller outlet increasing the surface area of the outlet to allow the air to settle as it leaves the impeller.


The design enhancements included on the RadiCal impeller range has seen a step-change in fan efficiency.

Improving the aerodynamic efficiency has also produced the benefit of a lower noise fan solution.

RadiCal Fans already available in the RS Components Catalogue

Radical Motorised impellers are currently available in sizes from 133mm diameter to 225mm…




230V/1~ EC -(802-9447)


230V/1~ EC - (830-3023)

230V/1~ EC - (802-9440)

230V/1~ AC - (841-4911)

115V/1~ AC - (860-0239)

24V DC - (920-9206)


230V/1~ EC - (830-3032)

230V/1~ EC - (802-9444)


230V/1~ EC - (802-9453)

230V/1~ AC - (830-3029)

115V/1~ AC -(860-0235)


230V/1~ EC - (802-9456)

230V/1~ AC - (825-7740)

230V/1~ AC - (825-7746)


New Products on the Horizon

To further enhance its capabilities the RadiCal motorised impeller has been incorporated into a scroll housing.

The scroll has been designed to improve the static efficiency of the fan as an air delivery system, to reduce noise and to add control functionality. The new fan has an incorporated rotary vane anemometer on the outlet that precisely measures the flow rate passing through the fan. External and on-board temperature and humidity sensors can monitor the air passing through the fan to maintain a comfortable, healthy environment. In addition, the fan is equipped with Modbus-RTU communication allowing it to communicate with environmental management systems which can receive commands and report back operating data.

If this product is of interest, further information can be requested via the product plus area on the RS Components web pages -


By studying the transition of air through the standard fan, ebm-papst have been able to enhance product design making the backward curved motorised impeller quieter and more efficient. In addition to smoothing the flow of air as it passes through the impeller additional functionality has been added to the scrolled version. These enhancements provide state of the art performance and control for today’s modern-day air movement requirements.


My background is in Mechanical & Production Engineering however working for ebm-papst that has expanded into electro-mechanical, some electronic and acoustic engineering. When it comes to acquiring and passing on knowledge, I try to keep it as simple and as least painful as possible. I am happy to receive feedback and if there are any questions that arise from anything that gets published. If I don't know the answer to your question immediately, I am sure that I know someone that can help.

2 Sep 2019, 13:12