The efficiency of GreenTech EC motors leaves little to be desired. That said, a high motor efficiency level does not necessarily guarantee that the system as a whole will be just as efficient. Measurements have shown that the successful RadiPac fans still offer potential for improvement in this respect. Which is why the flow machine has now come under scrutiny again at ebm-papst.
Following a detailed loss analysis and qualification process, the modification work mainly concentrated on the air inlet into the impeller, the positioning of the external rotor motor in the impeller and the blade profile of the impellers. With a view to improving the air flow (Fig. 1), the aim was thus to increase efficiency whilst at the same time reducing noise emissions. After all, the acoustic performance of a fan is considered to be one of the important features in most applications.
Varying degrees of turbulence occur in the intake area of the fan due to the often confined installation space. Optimisation of the fan cannot compensate for such inflow disturbance. The turbulence arising from the installation situation can however be reduced by modifying or optimising the inflow of air to the fan, which also helps to keep down the associated annoying low-frequency noise. This was the reason for developing an optional special air inlet grille which has a straightening effect on the inflowing air (Fig. 2). The grille drastically reduces noise-generating disturbance in the inflowing air. Regardless of the building structure and the installation situation in the housing, the fans then attain noise levels comparable to operation under laboratory test conditions (Fig. 3).
An intelligent combination of components is the key to achieving good system performance. Which is why the inlet nozzle of the new RadiPac fans is designed to perfectly match the impeller with its aerodynamically optimised blade channel. This lessens turbulence right at the air inlet, thus reducing flow loss and at the same time eliminating one of the causes of noise nuisance. The transition from the inlet nozzle to the impeller cover plate has also been modified to produce a clearly defined gap flow. As a result the turbulence in the air flow, which would narrow the effective flow cross-section, is reduced at this point as well. This modification again adds to the efficiency of the system as a whole. An optimally positioned pressure tap for air flow measurement is also provided as standard, making commissioning easier for users.
The mechanical design and aerodynamic properties of the new aluminium
airofoil blades provide greater efficiency. The hollow profile of the blade keeps the weight of the impeller to a minimum whilst maximizing the rigidity. The extremely rigid impeller also permits high circumferential speeds.
On account of the gentle rounding of the blade inlet, there is little inflow loss. The profiled contour guides the air flow through the blade channel with minimal loss before it leaves the impeller with hardly any turbulence thanks to the thin trailing edge. The specially shaped impeller base plate routes most of the outflowing air in axial direction. This reduces the deflection losses in the air conditioning device as well as the pressure drop when installed (Fig. 4). An added advantage is a lower noise level.
The position of the motor in the impeller has also been altered to achieve a good compromise between the compact design of the fan unit as a whole and the best possible location of the motor in the impeller from an aerodynamic point of view. The centrifugal impellers are attached to the rotor, in other words directly to the “housing” of the external rotor motor. This particularly helps to reduce the axial dimensions whilst at the same time improving cooling, as the motor is cooled by the air conveyed by the fan. In addition, the entire rotating assembly made up of rotor and impeller is dynamically balanced in two planes at the production stage to ensure extremely low-vibration operation.
There is yet another convincing aspect to the centrifugal fans. Alongside the high-performance impeller with inlet nozzle, a GreenTech EC motor and control electronics, the RadiPac product range for use in air handling units includes additional mechanical components (Fig. 5) to provide customers with complete ready-to-install fan units. In contrast to other concepts – employing asynchronous or PM motors for instance – users do not have to go to the trouble of purchasing, fitting, connecting and matching up individual motors, frequency converters and impellers.
What’s more, there is no need for any additional electronic filters or screened cables with RadiPac fans, as the motor and the electronics integrated into the motor system are already perfectly coordinated and situated close together. External motor circuit-breakers are also superfluous. That’s what Plug & Play for ventilation technology is all about. Our certified product selector (Fig. 6) permits the realistic modelling of the operating situations to be expected for a specific application on the basis of the measured performance data of the fan. Absolute planning reliability is thus guaranteed.
The infinitely variable speed control typical of EC motors also enables the fan performance to be exactly adapted to individual requirements. Either the standard 0-10 V DC/PWM input or the Modbus-RTU interface can be used for communication.
As an added feature and to help choose the right fan, the ebm-papst “Product selector” software with integrated “Black Box” module is available for incorporation into customer device configuration programs. With the new selection program, RadiPac fans can be picked out on the basis of the operating point. If there are several fans in the specified performance range, the aerodynamic and acoustic data displayed can be used to help choose and document the most suitable model. Another option available is calculation of the life cycle costs for the fans selected. As well as using the operating point, it is also possible to perform selection by way of the type designation. The data sheets can be created in pdf format and show not only the nominal data of the fan but also the performance data at the specified operating point together with the suction and pressure side sound power levels over the octave band (Fig. 6).