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 a no-brainer, and also allows great flex­i­bility thanks to indi­vidual speed adjust­ment. Devel­op­ment is contin­uing at a steady pace. 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 thanks to their special design, which helps prevent the heat pumps from becoming a disrup­tive factor and allows them to blend in well with their surround­ings. 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 low back pres­sure when the heat pump design requires this.

Axial fan with high pres­sure reserve

Ice forma­tion partic­u­larly affects evap­o­ra­tors when humidity precip­i­tates as ice on the heat exchanger at cold ambient temper­a­tures. This reduces the air routes and the drag, and so too the back pres­sure. The fans then have to offer signif­i­cantly 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 only reduces 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 oper­a­tion.

The fan, which is avail­able from summer 2023 in sizes 450, 500 and 630, typical of heat pumps for single- or two-family homes, has also been fitted with an air inlet grille. This Flow­Grid, which acts as a recti­fier for air flow, dras­ti­cally reduces noise-gener­ating distur­bances in the air flow. This reduces the sound pres­sure over the entire frequency range, in partic­ular the disrup­tive blade passing noise, i.e. unpleasant “humming” in the low frequency range (Fig. 3).

At the same time, the air inlet grille serves as a motor suspen­sion and, if neces­sary, the equip­ment manu­fac­turer can insert heating tape. The new axial fan weighs 30% less than the compa­rable HyBlade version with steel wall ring. This means that less weight has to be handled during the instal­la­tion and the compact dimen­sions often make it possible to opti­mize the design of the end device. The AxiEco Plug-in fans are supplied as a ready-to-install plug & play solu­tion, including nozzle plate and Flow­Grid.

Quiet fan with three blades

For air/water heat pumps, where high back pres­sure tends to be the excep­tion due to their design, the three-blade AxiTone – initially avail­able in size 450 mm and later in sizes 500 and 630 mm (Fig. 4) – is the obvious choice. Its char­ac­ter­istic curve is flatter, it supplies large volumes of air, and, as the name suggests, it makes very little noise during oper­a­tion (Fig. 5).

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 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 partic­ular atten­tion must be paid to minimum noise emis­sions, there­fore also benefit from this quiet axial fan. The AxiTone is avail­able as a ready-to-install motor-impeller combi­na­tion in both airflow direc­tions, i.e., intake or blowing, and option­ally with a guard grill and support ring. It is also suit­able for appli­ca­tions with flam­mable refrig­er­ants.

Inverter elec­tronics for effi­cient and low-noise compressor drives

Mean­while, 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, among other things, for speed-controlled perma­nent magnet synchro­nous machines (PSM), as typi­cally used in compres­sors (Fig. 6). The new elec­tronics, the samples of which will be avail­able from Q3/2023 and which will be avail­able 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 %. For users, this means an annual saving of 70 euros at an assumed elec­tricity price of 35 cents per kilo­watt hour. 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 use a cold plate for cooling.

The active three-phase PFC level inte­grated into the inverter elec­tronics (power factor correc­tion filter) 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.

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