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01 ° 2013Technology by ebm-papst°12Early failure detection: Integrateddiagnostic system for fans°04°16ActionBrake: Fans with a wear-freerun-down brakeGreenTech EC motors: External rotormotors need no rare earth magnets°08°20New diffuser AxiTop – Less noiseand more effi ciencyNRV 77: Optimised componentsfor gas condensing boilers

04ACTIONBRAKE08DIFFUSERAXITOP12INTEGRATEDDIAGNOSTIC SYSTEMCONDENSING BOILERSYSTEM NRV 7772001°2013GREENTECHEC MOTORS162 techmag 01°2013

ACTIONBRAKEFans with a wear-freerun-down brakeMore safety and air fl ow, less turbulence and operating noiseFigure 1: The new fan with integrated Action-Brake is just as compact as the conventionalmodels.Fans are part of the standard equipment in almostall industrial facilities today. They cool, suction,regulate humidity and do much more. Thebenefit is plain to see, but compact dimensionsand high blower output with low power consumptionalso bring some limitations to safety. A standardfan today runs at a relatively high speed. Thefact that the bearings move easily means thatthe fan has a long run-down time when shut off.Since rotating parts always entail danger of injury,safety is guaranteed via guard grilles. These,however, cause aerodynamic disadvantages. Anew approach that avoids these disadvantageswith a greater level of safety is an active brakein the fan. If the fan gets switched off, the wearfreeelectronic brake reduces the run-down timeto less than two seconds. The kinetic energy isquickly dissipated, thereby drastically reducingthe risk of injury.Rotating masses store energy. This property,which is desired in flywheels, becomes a sourceof danger in other rotors. This also applies to fanswhose rotors transfer the energy of the motor tothe air through blades. Large volumes of air canbe moved at high speeds, even with compact dimensions.Simultaneously, however, the energystored in the impeller also increases, and with itthe potential hazard. For protection, the fan specialistebm-papst from St. Georgen now provides- in addition to guard grilles - a new, aerodynamicallybetter alternative: ActionBrake, the activebrake integrated in the fan motor. In less than twoseconds it reduces the speed to harmless valueswithout requiring additional installation space orgenerating additional drag, as with a guard grille(Figure 1). By way of comparison, a standard fanwithout a brake requires 20 seconds to reducethe speed to harmless values.State of the art of technology If a servicetechnician switches a device off and opens it,the rotating rotors of the fans pose a substantialpotential hazard. This applies particularly tomodern compact fans, which operate at highspeeds in order to overcome high counterpressureor to generate a large air flow. At the same4techmag 01°2013

ActionBrake, the active brake integrated inthe fan motor reduces the speed to harmlessvalues in less than two secondstechmag 01°20135

ACTIONBRAKEFigure 2 (left): Clearly visible, guardgrilles not only stand out visually, theyalso impede the air flow.with guard grilleinlet sidesingle fan@ 8900rpmwith guard grille inletside + outlet sideOverall Level 88.2 dB(A)/1pW 84.8 dB(A)/1pW 88.0 dB(A)/1pWTable 3a: Comparison of Sound Power Level; Fans with and without a guard grilleBecause of theintegrated rapid brakingthe fan can operate atoptimum efficiencytime, low-friction bearings operate in the fansto increase the energy efficiency and servicelife. Consequently, the energy stored in the rotormakes for long run-down times. If the rotation issuddenly stopped by an object or even a finger,the kinetic energy abruptly discharges. This leadsto damage or, in the worst case, injury. To preventthis, regulations stipulate the use of protectionagainst accidental contact with quickly accessiblefans, in other words, guard grilles (Figure 2). Preciselywith high-peformance fans, however, thisnegates a portion of the sophisticated aerodynamicproperties. The grille generates turbulenceand thereby noise and counterpressure, resultingin lower blower output. Thus the grille acts as anenergy dissipator, like a gently and continuouslyapplied brake. The higher speed here generateseven more additional noise (Table 3a, Figure 3b).Safety without external components Thenew approach proceeds from integrated rapidbraking via the fan drive. This means that nomore disruptive obstructions are implementedin continuous operation; the fan can operate atoptimum efficiency. This also reduces installationeffort and eases the installation. The principlebehind the wear-free brake is simple as well astried-and-tested: The motor becomes a generatorand the generated current is then converted intoheat. The technology offers various options forthe design. Higher outputs require external brakeresistors; small outputs use the motor windingsas a brake resistor by means of a short-circuitswitch. Therefore the fan experts were set thetask of optimally designing the ActionBrake tomeet the needs of the fans, while doing withoutexternal components wherever possible. Througha series of tests, the optimum variant was foundto be the short-circuit switch for the motor windings.Initially in this case, however, very large currentscan arise at high speeds by means of theinduction. This means that the windings have toendure a high but short-term heat load, and thecontrol transistors have to be designed for thesepulse currents. Additionally, high currents incoils always means there will be a strong (counter)magnetic field. Thus there is a danger of themagnets in the rotor demagnetising. These problemsare solved by a suitable selection of componentsand configuration of the magnets. Thereforethe brake lifting magnet operates as reliablyand as long as usual.If the operating voltage is switched off, theelectronics enter the braking mode. In doing so,they draw their power supply from the loaded filtercapacitor. If the voltage decreases, the capacitoris recharged by short charging pulses from the“brake generator”. This is done to maintain thefunction, and thus the activation of the short-circuittransistors of the electronics, until the rotor6techmag 01°2013

ACTIONBRAKEpressure increase Δ pf [Pa]sound power level LWA [dB re 1pW]Figure 3b: Comparison ofcharacteristic curve; Fans withand without a guard grilleLEGENDair performance / single fanperformance with fingerguardacustics single fanacustics with fingerguardair flow Q [m 3 /h]comes to a standstill. To do so, the brake shortcircuit is temporarily disconnected. With a typicalfan, this enables braking times of under threeseconds. The inner heat capacity of the componentsand the maximum braking energy then producea temperature level that reliably lies belowthe maximum operating temperature of the componentsused. This ensures long-time operationthat is free of malfunctions and maintenance.The new active braking upon switchingoff the power supply at the fan opens new optionsto the user. In short, the brake lifting magnetbrings a whole series of benefits all at once:elimination of guard grilles and their installation,which translates into less noise, better output andlower costs by means of lower power consumption.Also in terms of logistics, the lower numberof parts is a noticeable plus. Thus the new brakelifting magnets save time and money while maintainingthe level of safety.The new brake liftingmagnets save timeand money whilemaintaining the levelof safetyAuthor is Dipl.-Ing (Graduate Engineer) (FH) Frank Heller,Development Engineer for Hardware, Basic and TechnologyDevelopment at ebm-papst St. GeorgenYou would like more information on this topic? Please addressyour question to: Frank.Heller@de.ebmpapst.comtechmag 01°20137

DIFFUSER AXITOPAxiTop – Less noise andmore efficiencyNew diffuser reduces exit losses in fansFor refrigeration and cooling equipment, theheat generated in the circulation process has tobe transferred to the ambient air via a heat exchanger.To accomplish this, fans move cool airthrough a heat exchanger and allow the heat todissipate. There is a whole range of options fordesigning and configuring especially efficient,quiet and durable fans. A new, passive component,the so-called diffuser, provides for a substantialimprovement in efficiency and noise. Itspressure-boosting effect minimises exit lossesand makes it easier to adapt the fan to commerciallyavailable heat exchangers.Ventilation and air-conditioning units usuallyrun in continuous operation, or at least with longoperating cycles. That make maximum economywith the input drive energy important, for everyadditional watt costs money and impacts the environment.For that reason, energy efficiency isan important criterion when choosing a fan. Today,statutory stipulations also play a role. Theefficient use of energy and resources is and willremain a global objective for the decades ahead.In Europe, the first tier of the ErP Directive becameeffective as of January 1, 2013. Againstthis background, it is no wonder that ultra-efficientEC technology is increasingly replacing conventionalAC technology as the fan drive of choicedue to its greater efficiency.Exit losses – the underestimated “energyguzzlers” Energy-efficient and quiet operationof the complete fan is a function of both the motorand the impeller, which the fan uses to movethe air volume needed to create the cooling airflow through the heat exchanger. Aerodynamicexpertise is needed when designing the impeller,for example to avoid separations and backflowswhich would cause both energy loss andunwanted noise. Even today, the impellers employedin the GreenTech EC fans satisfy the mostdemanding standards. But there is another pointwhich has to be taken into account when consideringthe efficiency of a fan:The inherent exit loss for fans with unimpededairflow is often an underestimated energyguzzler. Figure 1 (page 10) shows the power flowof the input drive power P o for an axial fan withunimpeded airflow. The drive power P o is split intostatic blower output (P us = product of the air flowand static pressure increase of the fan), which isof use to the user, and various losses caused by8techmag 01°2013

The new diffuser AxiTop reduces energyconsumption and is easily retrofittedthe conversion into this useful power. The largestloss factor in the process is the dynamic outputcomponent (P ud ) of air performance, which is alsoknown as exit loss. This is made up of the productof air flow and dynamic pressure. The motorand fan manufacturer ebm-papst has now pickedup this issue and has developed a new kind ofdiffuser, the AxiTop. Replacing the conventionalguard grille of the fan by the AxiTop diffuser(Fig. 2, page 10) significantly reduces losses atthe air outlet. Efficiency increases while operatingnoise is reduced at the same time. In principle,the diffuser works like a reverse nozzle, asfollows:Dynamic energy converted into static pressureEvery medium is only able to absorb a certainamount of heat energy for each degree Kelvin.The possible temperature difference and theamount of heat to be expelled define the coolingair flow required. This air volume has to be deliveredby a fan through the heat exchanger underconsideration. To do this, a pressure differentialis necessary which is sufficient to overcome theflow resistance of the exchanger. Normally, thedelivered air flows at high speed from the exit sideof the fan and dynamic pressure (p fd ) dissipatesinto the environment. Dissipation means that thekinetic energy of the flow is converted into turbulenceand then due to friction into heat thattechmag 01°20139

DIFFUSER AXITOPFriction lossesInternal lossesand gap lossesExit losses PudFigure 1 (left): Power flow of an axialfan with unimpeded airflowFigure 3 (right): The AxiTop diffuserallows part of the dynamic pressureto be converted into useful staticpressure by retarding the flow.PressureConversionof dynamicpressure intoheatAir performance PuDrivepower PoLEGENDCustomer benefi tStaticoutput Pusp fp fsStart of diffuserEnd of diffuserp fd_cgesp fd_caxp fd_cuAxis of rotationFigure 2: The AxiTop diffuser from ebm-papstprovides for a significant improvement ofefficiency and noise. Its pressure-boostingeffect minimises exit losses and makesit easier to adapt the fan to commerciallyavailable heat exchangers.is often no longer technically utilised. With theAxiTop diffuser, much of the dynamic kineticenergy is converted into static pressure (p fs ) byway of retardation. Physically, this is easy to explain:The total pressure generated (p f ) by a fanis the sum of the static pressure pfs and the dynamicpressure p fd_cges . In turn, taking the densityr into account, the dynamic pressure can be splitinto three speed components (cylinder coordinates),the axial component p fd_cax = /2*c ax² , thecircumferential component p fd_cu = /2*c u² andthe radial component p fd_cr = /2*c r² .In the diffuser, the axial and circumferentialcomponents of dynamic pressure (/2*c ges² ) arereduced due to the air slowing in the expandingcross section and, due to the conservation of energy(Bernoulli´s principle), the usable static pressurecomponent increases (see Fig. 3). Efficiencycan be significantly increased in this way if allcomponents are co-ordinated to be aerodynamicallyoptimised.In practice, the use of the AxiTop diffuserdoes not just mean lower energy consumption;it also means greater degrees of freedom for theuser and for the development engineer. The diffuserconfiguration can be optimised for differentcharacteristics, depending on the application concerned.Either a greater blower output is possiblewith unchanged energy input, or unchanged airperformance is possible with lower energy consumption.A diffuser can also greatly improve thenoise behaviour. This acoustic improvement isespecially interesting when fans are working is anoise-sensitive environment, for example in overnightoperation in ventilation and climate controlsystems in residential buildings or in rooms wherepeople meet and where there are also noise protectionregulations to be fulfilled.Significant potential to be exploited The potentialof the possible energy savings, increasedefficiency and noise reduction provided by an optimaldiffuser is substantial for common heat exchangerson the market. This has been confirmedin extensive test series. Figures 4a and 4b illustratea specific example. Replacing a normal fanwith a guard grille with the same fan with a supportbracket, guard grille and diffuser allows savingsof 27 % for energy consumption while enablingan operating noise level 7.2 dB(A) lower withthe same air flow (see Fig. 4a).Alternatively, if the greater efficiency of thefan with differ is exploited, it will deliver about 9 %more air flow with the same input power, and atthe same time noise emissions will be reduced by4.9 dB(A) (see fig. 4b). This value has been determinedon an exemplary customer application.Depending on the individual configuration, the optimisedefficiency can be used either to reducepower input or to increase air performance. So10techmag 01°2013

DIFFUSER AXITOPEnergy consumptionin kW2.521.51Outputin m 3 /h25,00024,00023,00022,00021,00020,00019,00018,000-27 %+9 %Noise development (LwA)in dB(A)90858075709085807570-7.2 dB(A)Noise development (LwA)in dB(A)-4.9 dB(A)Figure 4a (left, up): Energyconsumption and noise developmentare significantly lower withunchanged air performance.Figure 4b (left, down): Bloweroutput is increased and noisereduced with unchanged powerinput. Details from an exampleapplication.Figure 5 (right): The thrust range isnot affected by the AxiTop diffuser.The illustration shows the axial flowrate with diffuser on the left andwithout diffuser on the right.not only does the user save energy during operation;the design engineer for a climate controlsystem can get by with smaller heat exchangersurface areas. The space needed for the coolingunit can be reduced with unchanged or even improvednoise behavior and constant refrigerationcapacity. The reduction in the space needed isan argument which cannot be neglected, aboveall for larger heat exchangers. A diffuser is evenworthwhile if it subsequently turns out that thesystem does not have a sufficient refrigerationcapacity, e.g. in the case of a design error. It enhancesthe air performance without increasingnoise. In such cases, the installation of an additionalheat exchanger (and the associated costs)can often be avoided.Can be retrofitted and used in existing wallrings Equipping existing heat exchangers with adiffuser is easy and only requires a few changesto ventilation and air-conditioning units. The diffuseris fitted in place of the guard grille. Existingwall rings can still be used. The AxiTop diffuserfrom ebm-papst is just 250 mm high so it needsvery little space.With these dimensions, the developmentengineers have succeeded in achieving a verygood compromise. Physically, a diffuser cannotbe large enough in order to increase staticpressure. But dimensions which are as compactas possible are required in practice. CFD simulationscombined with parametric optimisationshave produced an excellent aerodynamic result.The change in the outflow profile causes the flowto split slightly, enabling the thrust range of thefan to be maintained. Figure 5 shows the differentcharacteristics of the exit speed cax, which is ofrelevance for the thrust range, with and withouta diffuser.The new AxiTop diffuser is designed for fansof the sizes 800 and 910. Versions for 500 whichare frequently employed with heat exchangerswill follow in the near future. It doesn´t matterwhether the fan works with GreenTech EC or withan AC drive. However, in the interest of energy efficiency,the combination with GreenTech EC fansin certainly preferable.Authors are Dipl.-Ing. (FH) Oliver Haaf, head of Product Development, Aerodynamicsgroup (left) and Dipl.-Ing (FH) Markus Engert, Predevelopment,Aerodynamics (right) at ebm-papst MulfingenYou would like more information on this topic? Please address your questionto: Oliver.Haaf@de.ebmpapst.com or Markus.Engert@de.ebmpapst.comtechmag 01°201311

INTEGRATED DIAGNOSTIC SYSTEMIntegrated diagnosticsystem for fansIndividual early failure detection takes intoaccount ambient conditionsThe life span calculation generally applied to fanstoday is based on the assumption of statisticalaverages. For this, there are various calculationformulas and evaluation criteria for loads such astemperature, speed or dust and humidity. If operatingconditions greatly deviate from the norm,this approach cannot provide any meaningful valuesfor the actual service life of an individual onsitefan. In order to achieve a more reliable statementabout the actual service life potential hereas well, in addition to general laboratory findings,the actual on-site loads have to be measured duringoperation, added up and included in the calculation.A new diagnostic tool for fans collectsthe relevant data for this and calculates the individualremaining service life under the actualoperating conditions. Thus operation and maintenanceof difficult-to-reach fans are decisivelyimproved and the reliability of the overall systemincreases.Statistical statements are only as good aspermitted by the assumed input data. Even thebest calculation program is not able to provideany realistic statement about the service life ofa product if the assumptions are incorrect. However,precisely with fans for exposed applicationsin a safety area or for systems that are difficultto access, such as cellular telephone stationson mountains, the most exact possible determinationof (remaining) service life is important tothe operators. Therefore it is ideal if the calculationincludes the actual load of the individualfan where it is used. If this takes place right inthe fan, and if the fan can issue an alarm signalwhen a configurable safety threshold is exceeded,that improves the reliability of the overall system.12techmag 01°2013

The Integrated diagnostic system uses the servicelife reserves of the fan, they no longer have to be“preventively” replacedTherefore there is no need for any cost-intensivepreventive replacements; that saves time, moneyand personnel.Existing evaluation method Existing, conservativecatalogue information regarding servicelife refers to an accepted, average operatingpoint; for example, service life L10 of 70,000hours at 40°C ambient temperature and 3,600revolutions per minute. Therefore they are moreof a standard value for the practical evaluation,since operating temperature and speed continuouslychange throughout the day and over theseasons, thereby affecting the service life. To thisare added unforeseeable factors, such as dustor humidity, which are taken into account only inspecial cases in the laboratory. Usually, currentevaluations of lifetime are based on laboratorytesting with defined standard conditions for temperatureand speed (Figure 1, page 14).For theoretical considerations of statisticsand testing, the average service life of the entireproduction is used. To achieve shorter testingperiods, often the thermal load is also set unrealisticallyhigh in order to achieve faster ageing ofthe components. Changing operating conditions,which always occur in real-world applications, aretechmag 01°201313

INTEGRATED DIAGNOSTIC SYSTEMFigure 1: In the endurance test room – the datafor the conventional life span calculation isacquired using the climate chamber.The new diagnostictool can determine theindividual service lifeof the fannot taken into consideration in this procedure.In order to make statistical statements concerningfans, it is enough to take into considerationthe service life of the rotor bearing. Failuresof the electronics or the motor winding are significantlysmaller and can normally be neglected.On this basis, ebm-papst developed a diagnostictool implemented in the fan that determines theindividual service life of the fan while taking intoconsideration the respective ambient and operatingconditions. This way the existing limitations ofthe operating statistics are completely redefinedby exact fundamental data and the latest methodsof calculation.New approach The new service life predictiontakes into account the individual history of the fanin its respective operation and thus statementsabout an expected remaining service life can bemade in individual cases using the applicationconditions. Changing temperatures (day/night cyclesor seasonal fluctuations) are taken into account,as are the accepted dust pollution on-siteand the actual speed. This data is used by theelectronics integrated in the fan to calculate theservice life (Figure 2).The new early failure detection is conceivedparticularly for users who can replace the fan onlyat high cost or at certain times (for example, re-Figure 2: Compact fans with high output andinternal self-diagnostics for service lifeService life or reliabilityService life and reliability are two terms thatare often used and equally easy to mix up. Servicelife, often abbreviated to L10, specifies aperiod in hours during which up to 10 percentof the devices will have failed. An L10 value of100,000 hours means that 90 % of tested deviceshave reached this run-time. In contrast,reliability is specified with the value Mean TimeBetween Failure (MTBF). Since fans normallycannot be repaired, a more apt designationwould actually be MTTF (Mean Time To Failure).Despite this, MTBF has become the expressionthat is most commonly used. Statements regardingMTBF values only apply during the plannedperiod of validity (e.g. usable service life).The failure rate can increase significantly afterthat due to signs of wear. A MTBF value of1,000,000 h (more than 110 years) means thatif 1,000 devices were running at the same time,one of them would fail every thousand hours,i.e. every 42 days (1,000 h * 1,000 =1,000,000 h).14techmag 01°2013

INTEGRATED DIAGNOSTIC SYSTEMabFigure 3a and 3b: The remainingservice life can also be outputdigitally via a PWM signal a) high, b)low or as an analogue value via anadditional RC element.mote measuring stations, radio buoys). With thenew options, the replacement intervals can beplanned in a timely manner or adapted to the individualrequirements. Fans no longer have to be“preventively” replaced, which reduces investmentand maintenance costs and increases operatingreliability.Real-world applications Instead of operatingon preset values, the new system uses data thatis updated on an ongoing basis, such as operatingspeed, ambient temperature and downtimes.Basic data, such as the bearing design (ball orsleeve bearing), the type of bearing lubricationand the grease used, and other ambient conditionsis preset. That way service life reserves canbe used, since the current forecast always takesinto account the overall history of the fan.The diagnostics system is based on empiricalcorrelations from real-world applications anddecades of endurance tests under various conditions.Customer-specific output formats, suchas L5 instead of L10, can be taken into account.The output can be wired out via either thealarm wire or an additional wire and can be calledup digitally. The remaining service life can alsobe output as an analogue value via a PWM signalto an RC element. Thus the product can beused nearly up to the actual end of its life withoutlosing reliability. That conserves resources,increases value creation and reduces costs ofprocuring replacements and maintenance costs(Figure 3a, b).The new diagnosticssystem not onlyconserves resourcesbut also reducesreplacements andmaintenance costsAuthors are Dipl.-Ing (Graduate Engineer) (FH) Frank Heller, DevelopmentEngineer for Hardware, Basic and Technology Development (left) and Dr.Lutz Ramonat, Research and Development Centre, Bearing Technology andReliability (right) at ebm-papst St. GeorgenYou would like more information on this topic? Please address your questionto: Lutz.Ramonat@de.ebmpapst.com or Frank.Heller@de.ebmpapst.comtechmag 01°201315

GREENTECH EC MOTORSExternal rotor motors need norare earth magnetsEnergy-effi cient GreenTech EC motors for fan technologyPermanently excited electric motors rely on permanentmagnets due to their function. Especiallystrong magnets can be produced in the sinteringprocess from compounds with rare earth materials,such as samarium cobalt or neodymium ironboron. After the artificial scarcity of these materialsand the resulting drastic rise in costs, theprices have been falling recently. However, sincenow as before China controls a large part of thequantity supplied, the user must continue toreckon with extreme price fluctuations. Likewise,availability is not guaranteed.Also in future, the costs for rare earth magnetswill be very difficult for the manufacturersof electric motors to calculate. Therefore permanent-magnetexcited electric motors, which areparticularly energy-efficient, are often regardedas expensive in user circles. It is not necessary,however, that each electric drive operating withhigh efficiency also really depends on strong rareearth magnets. EC motors with an external rotordesign, for example, which are used in energy-savingfans, run with “simple” and cost-effectiveand anywhere available ferrite magnets, andthey work at efficiencies of over 90 % in somecases.What is an EC motor? Since the terms in drivetechnology are not necessarily always used withclear and unambiguous definitions, it makes16techmag 01°2013

EC motors with an external rotor design are not necessarilydepending on strong rare earth magnetssense first to clarify which motors are actuallymeant in conjunction with the rare earth discussion.Whether a brushless DC motor (BLDC), abrushless permanent-magnet (BLPM) motor oran electronically commulated (EC) motor, alwaysmeans a permanently excited synchronous motor,which is operated with power electronics –mains-powered or with a DC power supply. Theso-called BLDC/BLPM motors are usually operatedwith square-wave currents (block commutation).The EC motors can be operated withsquare-wave currents as well as with sinusoidalcurrents (sinusoidal commutation). Doing the latterthe drive achieves a significant noise reductionover square-wave currents. The design withsinusoidal currents corresponds to the classicsynchronous motor. The basic function of the ECmotor is easy to understand (Figure 1, page 18):The rotor, which has permanent magnets, rotatessynchronously with the rotary field of thestator. Unlike the mains-powered asynchronousmotor, the rotor speed is not automatically coupledto the frequency of the supply voltage, butit is determined by the commutation electronics.Therefore operation of the EC motor always requiresadditional electronics. This determines theangular speed of the stator rotating field, at whichthe rotor synchronously rotates. The correlationsbetween voltage and speed and between currentand torque are largely linear. Consequently, withtechmag 01°201317

GREENTECH EC MOTORSFigure 1: Exploded drawing of the permanentlyexcited synchronous motor, also calledbrushless direct current motor or EC motor.The GreenTech EC fansare completely independentof the market trend ofrare earth magnetsrespect to its torque-speed characteristic, themotor acts like a DC shunt motor. To detect therotor position, either rotor position sensors are integratedin the motor, or the commutation electronicsmeasure the rotor position without sensorsvia the parameters field EMF and motor currents.The no-load speed depends on the appliedvoltage and the number of windings of the statorwinding. Therefore in the limits which are definedby the physical parameters (such as output power,torque, temperature rise etc.), nearly arbitraryoperating speeds can be implemented slip-free(synchronous with the stator rotating field), whichcan even lie above the power frequency, unlikethe mains-powered asynchronous motor. Forexample, if a fan is operated with an EC motor,the speed can always be adapted to the requirementsof the ventilation system or the process.In partial-load operation, therefore, the energyconsumption can be significantly reduced, becausethe required input power of a fan changesaccording to the speed to the power of 3. Asidefrom this, EC motors feature a significantly higherefficiency (Figure 2) than mains-powered AC motorsboth in partial-load operation and at full load,and they usually do this with a smaller size. Onereason is that EC motors do not require a magnetisingcurrent, so that current heat losses of therotor disappear. Another reason is the possibilityto implement a special winding arrangement witha low end winding (single-tooth winding / concentratedwinding, which reduce the winding losses).Even if the rare earth magnet discussion doesnot favour these motors, they are simply the bestchoice in terms of energy efficiency.Dynamic requirements determine thechoice of magnets With EC motors you arenot always forced to rely on the strong rare earthmagnets, because their excellent magnetic qualityis really needed only for highly dynamic servodrives, such as those used in robotics. On theone hand, compact dimensions are required; onthe other hand, however, the lowest possible rotormass is required to minimise the moment ofinertia. These requirements are attainable onlywith highly remanent and highly-coercive rareearth magnets. Therefore, manufacturers of suchservo drives primarily concentrate on reducingthe required magnet mass and height by meansof complex optimisations; and they have alreadyachieved very remarkable savings here.Motor and fan specialist ebm-papst Mulfingenis not even faced by this problem with itsfans, which are equipped with energy-efficientGreenTech EC motors. Despite the high efficiency,these drives run without rare earth magnets. Theexternal-rotor motor principle provides the keyfor this:18techmag 01°2013

GREENTECH EC MOTORSFigure 2 (left): EC motors have a significantlyhigher efficiency than comparableasynchronous motors.LEGENDEfficiency [%]EC motorThree-phase asynchronous motorAC capacitor motorShaded-pole motorShaft power [W]Figure 3 (right): Cutaway drawing ofcentrifugal fan with external rotor motor– the rotor rotates not in, but about thestator.The rotor is on the outside At this kind of motor,the still-standing part, the stator, is located onthe inside and is surrounded by the rotating part,the rotor (Figure 3). The externally positioned rotorrotates about the internal stator. Conditionedby this arrangement, the external rotor motor canachieve a higher torque (magnet volume, air gapsurface, radius) than the internal rotor motor ofthe same package length, the same magnet systemand the same magnet thickness (reducedmagnet volume, reduced air gap surface, smallerradius). By cleverly using the design parametersin the fan and blower area, an external rotor motorusing hard ferrite magnets can attain torquesand efficiencies which the internal rotor motorcan achieve only with rare earth magnets (becauseof the limited volume and mass). Unlikeservo drives, fans do not require high dynamics.Quite the opposite is required: a certain momentof inertia is desirable for the fans to have smoothstarting and acceleration behaviour. Without restrictionsrare earth magnets can be given up andferrite magnets can be used, which are not onlysignificantly more cost-effective, but also havestable market prices due to their availability.The motor design with an external rotor is advantageousfor fans in another regard as well.This way, the axial or centrifugal impellers can bemounted on the rotating rotor, thus directly on the“housing” of the motor (Figure 4). Compact dimensions,especially in an axial direction, are theconsequence and cooling is made simpler as themoved air of the fan is also cooling the motorhousing. The design with sinusoidal commutationalso provides for particularly low-noise operation.The energy-efficient GreenTech EC fans are thereforecompletely independent of the market trendof rare earth magnets.Figure 4: Energy-efficient fans whosemotors make do without rare earthmagnets.Authors are Dr. Jürgen Schöne, R&D Director of Aerodynamics and Motortechnology(left) and Werner Müller, Department Manager of Motor Development(right) at ebm-papst MulfingenYou would like more information on this topic? Please address your question to:Juergen.Schoene@de.ebmpapst.com or Werner.Mueller@de.ebmpapst.comtechmag 01°201319

CONDENSING BOILER SYSTEM NRV 77The new condensing boiler system NRV 77 allowsfor versatile adaptation to the different output andinstallation requirements20techmag 01°2013

CONDENSING BOILER SYSTEM NRV 77Versatile systemconsisting of a fan, gasvalve and venturi mixerOptimised components for a wide modulation range for gascondensing boilersAs an environmentally friendly heat source,gas has multiple advantages. In conjunction withmodern gas condensing boilers, the fuel is optimallyconverted into useful heat. Gas condensingboilers can be made very small, are long-lastingand very quiet. For practically every application,therefore, you can find optimally adapted heatingunits on the market. In order to build thesedevices as compactly as possible and still do justiceto the extensive variance, there is now a new,highly compact unit consisting of a fan, venturiand gas valve. It covers the large power rangefrom 2 to 35 kW and can be easily adapted to differentinstallation conditions in the gas condensingboiler. That saves time and money in designengineering and stock-keeping.State-of-the-art gas condensing boilersare available in a large number of variants. Theheart of such a device, however, is always thefuel management system, in other words, theoptimum dosing and treatment of the constantfuel-air mixture. With the NRV 77, ebm-papstLandshut, the specialist for state-of-the-art condensingboiler system technology is now offeringa new system for this, which allows for versatileadaptation to the different output and installationrequirements. The objective of the innovationwas to cover a large power range with the smallest,most compact dimensions possible, and simultaneouslybe able to vary the arrangement ofthe components when integrating them into thegas condensing boiler. Furthermore, the NRV 77takes into account the development of heat outputswhich are becoming ever smaller.The whole is more than the sum of its individualparts The fuel management system iscomposed of multiple single components. Alongwith the fan for the combustion air and the gasvalve, the newly developed venturi is the componentthat is the key to success. All three componentshave to be optimally matched to each othertechmag 01°201321

CONDENSING BOILER SYSTEM NRV 77Figure 1 (left): Typical CO 2curveCarbon dioxide content CO2 [%]Burner output Qc [kW]Figure 2 (right): NRV 77 withgas outletThe new NRV 77 gas-airmixture permits use in awide variety of differentgas condensing boilersfor the respectively required heat output. This isthe only way to guarantee efficient, low-emissioncombustion.The fan: always the correct air flow For conveyingfresh air, this means that the fan used canalways reliably move the air flow required for heatoutputs from 2 to 35 kW. The reason for this isthat a fan with a relatively small impeller diameteris used. This enables low air flows to be achievedwith minimum speeds that can still be controlledwell. To be able to cover the upper power range aswell, speeds of up to 11,500 rpm are required.However, the high speed and the long servicelife desired for use in heating require a specialbearing design. Therefore the bearing geometryand above all the lubrication have to be adapted tothese conditions. Carefully selected greases withideal viscosity, temperature behaviour and ageingstability are the decisive factor here. Intricate(long-term) test bench trials in conjunction withlong-time experience helped in the search for theoptimum lubricant for a speed-proof bearing withlifetime lubrication.The gas valve: large modulation range Forthe smallest heat outputs the required fuel gasquantities are downright minuscule. NRV systemshave a modulation range from 1 to 7, over whichthe air-fuel ratio of the combustion has to be controlled.What is called the main injection throttleof the gas valve is an important element here. Itconsists of a rotating plastic part, which is fastenedin place on a sheet. The parts have to be asflush as possible with one another to ensure thatthe entire gas quantity is fed through the main injectionthrottle and no leaks past the throttle candevelop. A leak would have a negative impact onthe minimum heat output. Moreover, the choke(plastic part) has to move easily, so that the airfuelratio of the combustion is configured at therated load.The objective here was to find the best possiblecompromise, which was achieved by temperingthe installed plastic part in the sheet metaland by optimising the sheet metal part. Thus itwas possible to achieve the goal of creating alargely leakproof main injection throttle that canbe moved ideally.The venturi mixer Venturi nozzles are frequentlyused to generate the required vacuum,through which the correct gas quantity is dispensedthrough the gas valve. A single venturi isnot able to cover the entire power range of thefan and gas valve. But each new venturi nozzlemeans a new mold.In order to find a flexible and cost-effectivesolution for our customers, we created a venturiwith an integrated displacement body. Its diame-22techmag 01°2013

CONDENSING BOILER SYSTEM NRV 77Venturi 3(27453.39569)2 15Figure 3: Powerrange of the NRV 77multi-venturi01°2013A = 131,5 mm 2Venturi InsertsVenturi 2(27453.39554)5,5 28A = 254,4 mm 2Venturi 1(27453.39553)7 350 5 10 25 20 25 30 35 40Heat Load [kW]Imprintebm-papstMulfi ngen GmbH & Co. KGBachmühle 2D-74673 Mulfi ngenPhone +49 (0) 7938 81-0Telefax +49 (0) 7938 81-110info1@de.ebmpapst.comA = 361 mm 2 23ter can easily be adapted in the overall tool by usingan insert, but this does not have any negativeimpact on the venturi´s performance. Additionally,the entire venturi can be flexibly attached to thefan with various mounting options. We call thispatented solution “multi-venturi”.Technology in numbers Thanks to the multi-venturisolution, system solutions (gas-air mixture)can also be cost-effectively provided in newtools in customer-specific, small annual productionvolume without investment costs. The productlaunch of the NRV 77 includes three performanceclasses, which cover the power range from 2 to35 kW. Additionally, depending on the installationconditions, the gas valve can be turned in up to 15different positions. A liquid seal is inserted betweenthe multi-venturi and fan housing. Thissealing point is 100 % tested in the plant.Due to its wide output-control range, the newNRV 77 gas-air mixture permits use in a widevariety of different gas condensing boilers. Stockkeepingis reduced as a result of the large outputvariability; the design can rely on uniform standardcomponents as a result of the flexibility. This notonly saves money and time in development andproduction, but also improves the market opportunitiesby providing better quality at a favourableprice.ebm-papstSt. Georgen GmbH & Co. KGHermann-Papst-Straße 1D-78112 St. GeorgenPhone +49 (0) 7724 81-0Telefax +49 (0) 7724 81-1309info2@de.ebmpapst.comebm-papstLandshut GmbHHofmark-Aich-Straße 25D-84030 LandshutPhone +49 (0) 871 707-0Telefax +49 (0) 871 707-465info3@de.ebmpapst.comwww.ebmpapst.comResponsible for content:Kai HalterEditor:Katrin LindnerLayout and production:Scanner GmbH, KünzelsauConcept:pr+co GmbHPhotography:ebm-papst,fotolia.com:p. 17 © alexanderpoppp. 13 © tae208p. 5 © by-studioAuthor Frank Schlopakowski is Manager New DesignDepartment / Systems at ebm-papst LandshutPrint:StieberDruck GmbHYou would like more information on this topic? Please addressyour question to: Frank.Schlopakowski@de.ebmpapst.comtechmag 01°2013

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