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Fans for air/water heat pumps

Demand for air/water heat pumps is rising; with output from 3 to 30 kW, they are a useful solu­tion for single- and multi-family homes. Low procure­ment costs, uncom­pli­cated instal­la­tion and a small foot­print make them an attrac­tive heating alter­na­tive, and not only in new build­ings. Modern EC fans play an impor­tant role in ensuring that such systems run very effi­ciently and econom­i­cally.

In prin­ciple, a heat pump works like a refrig­er­ator, which with­draws heat from the food stored in it and trans­fers it outside. Air/water heat pumps extract heat from the surrounding air and transfer the heat to the heating system, which warms the living areas or is used to heat water. Fans provide the needed air flow through the unit’s evap­o­rator, with the best results always being achieved when the fans are driven by modern EC motors. They are energy-effi­cient and very quiet, their speed is smoothly adjustable, and they have long service lives.

Axial or centrifugal fan?

There are two types of air/water heat pump; they are designed for indoor or outdoor instal­la­tion (Fig. 1a, 1b). The two types place different demands on the fans that are used (Fig. 2). In indoor instal­la­tions, outdoor air is drawn in through one duct and expelled later through another. Centrifugal fans are effec­tive for this appli­ca­tion as their design is suited to higher pres­sure require­ments.

Figure 1: Air/water heat pumps for instal­la­tion indoors (left) and outdoors (right). (Image | BDH/Solarpraxis AG)

They are very compact, bene­fiting the air/water heat pumps that are also installed indoors where space is usually limited. This also applies for systems that combine the heat pump and the resi­den­tial venti­la­tion unit (Fig. 3).

Figure 2: Char­ac­ter­istic pres­sure increase for axial and centrifugal fans. (Graphic | ebm-papst)

In contrast, space is usually not a problem for outdoor instal­la­tions, where the evap­o­rator is a sepa­rate unit and a refrig­erant line leads indoors. These config­u­ra­tions mainly use quiet-running axial fans.

With both axial and centrifugal fans in various sizes, motor and fan specialist ebm-papst offers the right fan solu­tion for every air/water heat pump. For example, the proven HyBlade axial fans or the new AxiBlade fans (Fig. 4) are well suited for use in air/water heat pumps in outdoor instal­la­tions.

The AxiBlades are partic­u­larly adapt­able to a wide range of appli­ca­tions, where they work with a high effi­ciency optimum. The new RadiCal centrifugal fans (Fig. 5), which are aero­dy­nam­i­cally opti­mized for energy effi­ciency and low noise emis­sion, are a good choice for air/water heat pumps in indoor instal­la­tions and combined systems. They are avail­able in diam­e­ters from 190 to 630 mm.

Figure 3: Air/water heat pumps combined with resi­den­tial venti­la­tion system. (Graphic | ebm-papst)

Energy-effi­cient and quiet

Modern EC motors are the driving force behind the fans. Users benefit from Green­Tech EC tech­nology in several ways. One of them is its energy effi­ciency. When gener­ating the desired heat output, heat pumps should consume as little primary energy as possible. Though the compressor consumes much more power than the fan, it still pays to have the fan work at the highest possible effi­ciency. Here there is no alter­na­tive to EC tech­nology.

Figure 4: AxiBlade fans work with a high effi­ciency optimum in a wide range of appli­ca­tions. (Image | ebm-papst)

Noise emis­sion is also impor­tant and always needs to be taken into account by those who use air/water heat pumps. The noise level is espe­cially impor­tant at night, when the limits imposed by DIN 18005 and “TA Lärm” (German tech­nical guide­lines for noise reduc­tion) must be complied with inside and espe­cially outside of build­ings. Good inter­play among fan impellers or blades with motors and elec­tronics is the key to quiet fan oper­a­tion. ebm-papst has opti­mized its blade and impeller geom­etry to achieve consid­er­able improve­ments in effi­ciency and noise emis­sion while also taking psychoa­coustic aspects into account (see text box) so that fan noise can be perceived as pleas­antly as possible. For quiet oper­a­tion, the fans can also be combined with guide vanes called Flow­Grid that reduce noise resulting from the condi­tions of instal­la­tion. Easy control of the EC motors used in the fans also has bene­fits since the speed can be adapted to actual needs such as speed reduc­tion for nightly temper­a­ture reduc­tion.

Smart and commu­nica­tive

Figure 5: RadiCal fans are quiet, smart and energy-effi­cient. (Image | ebm-papst)

The elec­tronics inte­grated in Green­Tech EC fans offer further capa­bil­i­ties in addi­tion to motor control. For example, multiple fans can be inter­con­nected via a MODBUS inter­face. Motor data can be read out and used for purposes like main­te­nance activ­i­ties. If the heat pump’s evap­o­rator is deiced when needed rather than cycli­cally, the current speed of the fan can be used for moni­toring; a decrease in speed can be a sign of ice forma­tion. Error messages from internal sensors can also be read out, enabling remote moni­toring of the fans in keeping with the Green­In­tel­li­gence philos­ophy.

The EC fans are also ideally equipped for the future as the use of natural refrig­er­ants is not a problem for them. Their energy effi­ciency and low noise emis­sions make them a future-proof solu­tion for the heat pump sector. 

Psychoa­coustics – how is a fan supposed to sound?

Psychoa­coustics is concerned with describing personal sound percep­tion in rela­tion to measur­able noise levels, i.e. it aims to explain why we perceive noises as pleasant or unpleasant. This is some­thing that phys­ical measure­ments of sound levels in test rigs are unable to address. For example, trumpet music and a construc­tion-site exca­vator have approx­i­mately the same sound power but are perceived psychoa­cousti­cally in completely different ways.

ebm-papst addressed this matter by setting up a special psychoa­coustic labo­ra­tory in which noise from fans in various config­u­ra­tions is played back for eight test subjects. Employees ques­tion the subjects after­wards to build up a scien­tif­i­cally founded data­base based on the following psychoa­coustic para­me­ters: loud­ness (unit: sone), sharp­ness (unit: acum), pitch (unit: mel), rough­ness (unit: asper) and fluc­tu­a­tion strength (unit: vacil).

Other impor­tant quan­ti­ties are tonality and impul­sive­ness. They can be measured with micro­phones and compared with comments made by the test subjects. Assess­ments by the test subjects are analyzed with statis­tical and psycho­log­ical methods. The results are used for product devel­op­ment. The ulti­mate aim is to develop a fan whose oper­ating noise is perceived as pleasant by as many test subjects as possible.

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