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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
Page 1 and 2: 01 ° 2013Technology by ebm-papst°
Page 4 and 5: ACTIONBRAKEFans with a wear-freerun
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Page 8 and 9: DIFFUSER AXITOPAxiTop - Less noise
Page 10 and 11: DIFFUSER AXITOPFriction lossesInter
Page 12 and 13: INTEGRATED DIAGNOSTIC SYSTEMIntegra
Page 14 and 15: INTEGRATED DIAGNOSTIC SYSTEMFigure
Page 16 and 17: GREENTECH EC MOTORSExternal rotor m
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Page 20 and 21: CONDENSING BOILER SYSTEM NRV 77The
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