Today’s heating systems demand concepts based on renew­able ener­gies. There­fore, heat pumps are becoming ever more popular in both new build­ings and reno­va­tions and are subsi­dized by funding in many cases. They are becoming an impor­tant pillar in creating more sustain­able heat gener­a­tion. Today more than half of new construc­tion projects are equipped with this. Air-to-water heat pumps are widely used here due to their effi­ciency and their simple instal­la­tion and set-up. They use heat energy from the ambient air and transfer it to the hot water circuit via an inter­me­diate circuit with refrig­erant (Fig. 1).

Fig. 1 | Air-to-water heat pumps use the heat poten­tial from the ambient air and transfer this to the hot water circuit via an inter­me­diate circuit with refrig­erant (creator: Bundesver­band Wärmepumpe e.V.)

What fan options are there?

However, the step-by-step plan of the F-Gas Regu­la­tion (Regu­la­tion (EU) No. 517/2014) governs the use of partially halo­genated hydro­flu­o­ro­car­bons (HFCs) (Fig. 2). So in the long term, there is no way around the natural alter­na­tives. However, these are flam­mable in most cases.

The reason for this is simple: a low GWP value requires a rapid decom­po­si­tion of the refrig­erant when it enters the atmos­phere. This can only be assured if it is chem­i­cally reac­tive, but high reac­tivity typi­cally goes hand in hand with a high level of flam­ma­bility. When devel­oping refrig­er­ating systems and air condi­tioners, house­hold refrig­er­a­tors and heat pumps, manu­fac­turers must there­fore ensure that they only use compo­nents that meet the applic­able stan­dards for handling flam­mable refrig­er­ants.

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 fault occurs. In prin­ciple, this can be achieved in various ways. One method, which is very time-consuming, is using restricted-breathing hous­ings that prevent elec­tronics and flam­mable atmos­pheres from coming into contact with one another. Another option is using an addi­tional, smaller ATEX fan, which ensures reli­able venti­lation of the unit. However, this prin­ciple of contin­uous venti­lation is only rarely used, e.g. in chillers. Most manu­fac­turers of air-to-water heat pumps prefer to use compo­nents that are approved for use with flam­mable refrig­er­ants.

Fig. 2 | The step-by-step plan of the F-Gas Regu­la­tion (Regu­la­tion (EU) No. 517/2014) governs the use of partially halo­genated hydro­flu­o­ro­car­bons (HFCs). (Graphic | ebm-papst)

Drive design in accor­dance with EN 60335-2-40

Using ATEX-approved fan motors is always possible but they are often over­sized and expen­sive. Motor and fan specialist ebm-papst there­fore offers an alter­na­tive specially designed for use in air-to-water heat pumps. For selected fan drives in sizes 55, 74 and 84, 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, which is very well suited to new build­ings and building reno­va­tions due to its good heat transfer capacity and its low GWP value, has an igni­tion temper­a­ture of 470 °C. The elec­tronic assem­blies, which have been tested and certi­fied accord­ingly, ensure that their maximum surface temper­a­ture always remains below 370 °C, even if a fault occurs, and as a result 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.

High energy effi­ciency and low noise emis­sions

Energy effi­ciency and noise char­ac­ter­is­tics are also impor­tant aspects when selecting fans for heat pumps. Modern EC motors are the driving force behind the fans. Users benefit from Green­Tech EC tech­nology in several ways: One of them is thanks to its energy effi­ciency. When gener­ating the desired heat output, heat pumps should consume as little primary energy as possible. The compressor consumes much more power than the fan, but it still pays to have the fan work at the highest possible effi­ciency. That is why there is no alter­na­tive to EC tech­nology here too (Fig. 3).

Fig. 3 | When providing the desired heat output, heat pumps should consume as little primary energy as possible. It pays off if the fan oper­ates at the highest possible effi­ciency (green char­ac­ter­istic curve ‘RadiCal’ with Green­Tech EC tech­nology, red char­ac­ter­istic curve for conven­tional centrifugal fan with AC tech­nology: P1=Power consump­tion, Pfa=Air perfor­mance curve) (Graphic | ebm-papst)

Another advan­tage, the noise char­ac­ter­is­tics of the EC fans, becomes partic­u­larly impor­tant at night when the limit values of the applic­able legal regu­la­tions must be observed inside and, most impor­tantly, outside the building. To keep noise emis­sions low, large fans should operate in the low speed range as far as possible. It goes without saying that the EC motors used in the fans are easy to control, as the speed can be further reduced at night without a problem.

This means that switching off the heat pump to avoid trouble with the neigh­bors is not neces­sary. If the speed of the example fan is reduced by just 100 rpm, the noise can be reduced by more than half (Fig. 4).

Fig. 4 | Depen­dency of sound pres­sure on the speed with a centrifugal fan. If the speed of the example fan is reduced by just 100 rpm, the noise can be reduced by more than half. (Graphic | ebm-papst)

Good inter­play between fan impellers or blades with the motor and elec­tronics is another key element for quiet fan oper­a­tion. ebm-papst has opti­mized its blade and impeller geom­etry to achieve consid­er­able improve­ments in aero­dy­namic effi­ciency and noise emis­sion. Psychoa­coustic aspects were also taken into account to ensure that fan noise comes across as pleas­antly as possible. For quiet oper­a­tion, the fans can usually be combined with guide vanes.

This Flow­Grid reduces noise resulting from the condi­tions of instal­la­tion. This ensures that the heat pumps operate quietly at all times. The range of fans that meet the applic­able stan­dards for flam­mable refrig­er­ants is being contin­u­ously expanded so that a suit­able design can be found for each perfor­mance class.