28 - 29 October 2025 // Nuremberg
European Heat Pump Summit Newsroom
Fans and inverter electronics: For energy-efficient and quiet heat pumps
Air-water heat pumps now enjoy a high level of acceptance in heating technology and are becoming an important pillar of more sustainable heat generation. There is demand for efficient and, most importantly, quiet systems suitable for indoor, outdoor or hybrid use (Fig. 1), using natural refrigerants, and whose output can be intelligently adapted to the actual conditions. This is where fans come into play that not only operate economically at optimum efficiency and with low noise levels, but can also communicate and be intelligently networked. As the noise and power consumption of the speed-controlled compressor drive also has to be factored in, there is also a need for inverter electronics that reduce operating noise through optimum commutation and also increase the energy efficiency of the heat pump.
The demands placed on the components installed in heat pumps are high, with durability, low noise, robustness and efficiency at the forefront. Although the compressor requires the largest amount of energy of the individual components, the fans should also be scrutinized carefully when considering efficiency. Various aerodynamic adjustments, such as an integrated diffuser and winglets, can further increase efficiency while simultaneously reducing noise. Given the high efficiencies, the use of state-of-the-art EC technology in the fan’s motor has become an easy choice, and also allows great flexibility thanks to individual speed adjustment and intelligent networking options. Fans are being continually developed. Motor and fan specialist ebm-papst, which offers both centrifugal and axial fans in various designs for air/water heat pumps operating indoors or outdoors, has now developed two new fan series for particularly noise-sensitive outdoor areas. Both are suitable for use with natural and flammable refrigerants and are particularly quiet. While the AxiEco plug-in is suitable for heat pumps requiring a large pressure reserve for the evaporator, the AxiTone is geared more towards delivering higher air flow at a low back pressure when the heat pump design requires this.
Axial fan with high pressure reserve
Ice formation is a particular issue for evaporators when humidity settles as ice on the heat exchanger at cold ambient temperatures. This reduces the air routes, and the drag, i.e. the back pressure, increases. The fans then have to offer much greater pressure reserves. This is where the new AxiEco Plug-in comes in (Fig. 2). Studies have shown that its flow technology reduces ice formation and its air flow reduces only very slightly as the pressure increases. This is also an advantage for heat pumps, which heat in winter and cool in summer, as the operating points then vary depending on the mode of operation. The fan was also equipped with an air inlet grille. This FlowGrid, which acts as a rectifier for air flow, drastically reduces noise-generating disturbances in the air flow (Fig. 3).
Quiet fan with three blades
The three-blade AxiTone is ideal for air/water heat pumps where high back pressure is more of an exception due to their design. Its characteristic curve is flatter, it supplies large volumes of air, and, as the name suggests, it makes very little noise during operation (Fig. 4). The blade geometry plays a key role in both respects, as it has been optimized to aerodynamic criteria. The large area and steep inclination ensure high air flow, and the sickle-like shape reduces turbulence and hence noise generation. Other new features include the serrations, structures like saw teeth, at the front edge of the blade. They also have a positive effect on the noise characteristics, as they minimize the tonal components of noise. Condensers in residential areas, where minimum noise emissions are particularly important, also benefit from this quiet axial fan, which is also suitable for applications with flammable refrigerants.
Flammable natural refrigerants as a challenge
The step-by-step plan of the F-Gas Regulation (Regulation (EU) No. 517/2014) governs the use of partially halogenated hydrofluorocarbons (HFC) as a refrigerant in air/water heat pumps (Fig. 5). So in the long term, there is no way around the natural alternatives. However, these are flammable in most cases. For fans that provide the necessary air flow in heat pumps through the evaporator, this means that their electronics must not become an ignition source, even if a leak occurs. It is always possible to use ATEX-approved fan motors, but they are often oversized and expensive. ebm-papst therefore offers an alternative, specially designed for use in air/water heat pumps:
For fan drives, the electronics circuits have been modified to comply with EN 60335-2-40 for heat pumps with flammable refrigerants, i.e. the maximum surface temperature must be at least 100 kelvin below the ignition temperature of the refrigerant used in the event of a fault. Propane, for example, has an ignition temperature of 470°C. The electronic assemblies that have been tested and certified then ensure that their maximum surface temperature always remains below 370°C, even in the event of a malfunction, so that they do not become an ignition source. The fans approved for use with A3 refrigerants in accordance with EN 60335-2-40 with maximum fill quantities of up to 1 kg or 5 kg (depending on the installation site) are available in many axial and centrifugal variants, covering the widest variety of applications for air-to-water heat pumps for outdoor use and for indoor use (Fig. 6).
Focusing on psychoacoustics
Air/water heat pumps will never operate completely silently and the more dense the buildings are, the more the neighbors may get disturbed by noise pollution. It is by no means just the measurable sound pressure level that is crucial, but also human noise perception. Here, psychoacoustics is implemented with examination methods, as usually it is not sufficient to observe only the limit values of DIN 18005 and TA noise. The values defined in the guidelines and standards, which can be measured on the test stand, have little to do with individual human noise perception. Until now, standards and directives have not adequately addressed issues such as tonality, i.e. the relationship between tones. ebm-papst tackled this issue early on and set up a special psychoacoustics laboratory for test subjects, who listen to the operating noise of heat pumps and the fans installed in them are played in various configurations (Fig. 7). Developers question the subjects afterwards to build up a scientifically founded database.
The results are incorporated into in-house fan development, but also provide information about the tested air/water heat pumps and which fans are best suited to the individual installation scenario. Ultimately, the aim is to ensure that the operating noise of a high-quality heat pump that is already very low is perceived as pleasant by the widest possible group of test subjects. Research on psychoacoustics is in full swing and we can look forward to more results. As part of a doctoral thesis carried out at ebm-papst, for example, it has already been possible to develop a metric (Fig. 8), which is now used for psychoacoustic evaluation in the end device. The aim of this metric is to create a correlation between the subjective perceived noise quality, which is represented in different "dimensions", and objectively measurable variables, which are then to be incorporated into corresponding standards as a next step. For this purpose, subjective dimensions of perception with measurable psychoacoustic variables are brought into play. The closer the correlation coefficient r is to 1, the more suited the model to depicting the subjective aspects of perception through objective (measurable) ones. The acoustic quality Q, which then represents the fan's perceived noise, should be as high as possible.
Inverter electronics for efficient and low-noise compressor drives
Meanwhile, however, ebm-papst is not only focusing on offering efficient and quiet fans. Based on many years of experience with EC motors, their commutation electronics, and heat pump applications, the company has now developed inverter electronics that are suitable, for example, for speed-controlled permanent magnet synchronous machines (PSM), as typically used in compressors (Fig. 9). The new electronics, with output powers of up to 3.5 kW, 7.5 kW and 12 kW, offer several advantages here.
The ebm-papst commutation method, which has been optimized over decades, considerably reduces noise development; at the same time, efficiency is increased. For example, in a heat pump with a 7.5 kW compressor drive, the COP value (Coefficient of Performance) could be increased by 3.5 %. Depending on the variant, the controls also “detect” whether they are operated in one or three phases, and switch over automatically depending on the type of voltage available in the heat pump. The electronics are also flexible in terms of their cooling. Thanks to their modular design, it is possible to use water or air cooling, or a cold plate. The active three-phase PFC level integrated into the inverter electronics (power factor correction filter) also ensures good EMC properties. No additional measures are required to comply with the standards with regard to current harmonics. Given that, depending on the size of the heat pump, conventional expansion valve assemblies can easily weigh up to 20 kg, the weight saving and the reduced wiring effort required by active PFC are considerable. The low weight of the heat pump simplifies its entire handling, from production to transport and installation by the end user. As a competent partner for heat pump manufacturers, ebm-papst is already planning the next steps to become a system provider. In the future, further components will be integrated into the inverter electronics, for example commutation for the fan drive and the control of a heating rod.
About ebm-papst:
The ebm-papst Group, a family-run company headquartered in Mulfingen, Germany, is the world’s leading manufacturer of fans and motors. Since it was founded in 1963, the technological leader has set international industry standards with its core competencies in motor technology, electronics, digitalization, and aerodynamics. ebm-papst offers sustainable, intelligent, and tailor-made solutions for virtually every requirement in ventilation and heating technology.
In the 2022/23 financial year, the Group generated turnover of EUR 2.540 billion. It employs just under 15,000 people at 30 production sites (including in Germany, China, and the U.S.) and in 50 sales offices worldwide. ebm-papst sets the benchmark in almost all sectors, such as ventilation, air conditioning and refrigeration technology, heating technology, information technology, mechanical engineering, intralogistics, and medical technology.
Authors: Marcel Rössler, Global Business Development Heat Pumps & Inverter Heating Technology and Patrick Stern, Product Manager, both from ebm-papst Mulfingen