A small impeller with a huge impact

The mate­rial heat is made of: Biomass heating systems – using wood chips for example – are enjoying double-figure growth rates

To start with, Dr Johann Gruber was some­what scep­tical when Thorsten Hartl, sales manager at ebm-papst Austria, suggested using an EC induced draft fan for a new wood chip heating system instead of an AC model. “We had actu­ally been consid­ering a larger impeller to achieve a greater air perfor­mance,” recalls the head of devel­op­ment at Hargassner. The company manu­fac­turing wood chip, pellet and wood burning systems based in Weng im Innkreis in Upper Austria is one of the leading Euro­pean special­ists in the field of biomass heating tech­nology – a market enjoying double-figure growth rates. Hartl’s sugges­tion was however very much in keeping with the ideas of Gruber and Anton Hargassner, the junior director of the company: They were looking for a way of enhancing the effi­ciency of the wood chip heating method which would keep emis­sions to a minimum whilst consuming less power than earlier models and at the same time permit­ting a compact design.

After initial discus­sions with Hargassner, Hartl soon realised: Only an EC motor is capable of satis­fying such require­ments. Despite some initial scep­ti­cism the deci­sion was there­fore taken to try out EC tech­nology for the first time in the biomass branch. “It came as quite a surprise to discover that we reached the air perfor­mance target with room to spare in spite of the smaller impeller.” This was however only possible on account of super-synchro­nous speeds above 2,800 rpm.

Central control instru­ment

No mean feat, as the perfor­mance of a heating system is largely deter­mined by the air throughput in the boiler. The induced draft fan plays a crucial role: It produces a vacuum in the combus­tion chamber and thus creates the mixture ratio required for optimum combus­tion. This ratio is measured with a Lambda probe – a sensor which controls the combus­tion air compo­si­tion on the basis of the measured values. And the more finely the air throughput can be regu­lated, the better the output can be modu­lated. This is partic­u­larly impor­tant when burning wood.

Optimum combus­tion guar­an­teed: The induced draft fan produces a vacuum in the combus­tion chamber and so controls the mixture ratio

When compared to other forms of energy, the fuel to which Hargassner has been dedi­cated for 30 years almost always comes out on top: Whereas oil and gas prices are constantly on the increase and resources are dwin­dling, trees are regen­er­a­tive and supply heating mate­rial at a cost which has remained steady for years at a level well below that of fossil fuels. What’s more, the sustain­able raw mate­rial only gives off the amount of carbon dioxide on burning which it absorbed in the course of its growth and its climate effect is there­fore neutral.

Legis­la­tion governing permis­sible emis­sion levels is becoming ever more restric­tive and accord­ingly a crucial aspect in devel­op­ment work. Emis­sion values can only be reduced if the wood burns opti­mally, which in turn depends on the prop­er­ties of the induced draft fan. This however requires elec­tricity to operate. So the second major chal­lenge was to keep the power consump­tion as low as possible – not least because induced draft fans run for up to 2,500 hours per year. “Consumers take a close look not just at the fuel but also at the elec­tricity costs involved,” Hargassner stresses. Hartl is of the same opinion: “Power consump­tion is the bench­mark on which today’s purchasing deci­sions are based.”

Econom­ical, compact and powerful

Final assembly at Hargassner

EC tech­nology from ebm-papst enables Hargassner to reduce the power consump­tion of the new heater by 50 per cent. “With this very low level we are now the best in our branch,” as Hargassner is pleased to point out. In addi­tion, the DC motor permits infi­nitely vari­able speed control and thus ideal, low-emis­sion combus­tion. “The test author­i­ties told us that we are the only manu­fac­turers with such low emis­sion figures,” Gruber explains. “We can now achieve a far higher effi­ciency level, partic­u­larly in the low speed range.” A further advan­tage is that the flat impeller permits a compact design. “With an AC motor we would have had to use a larger model to achieve such perfor­mance and construct a giant induced draft unit to go with it.” Another aspect is ease of instal­la­tion. “We have adapted the EC induced draft fan in such a way that Hargassner now only has to tighten four bolts and connect the power and control cables,” explains Hartl.

Successful coop­er­a­tion

The new wood chip heating system has been on the market since March 2013 under the name ECO-HK and is intended primarily for customers in the agri­cul­tural and indus­trial sectors. The Austrian Ministry of the Envi­ron­ment and the Upper Austria region have already honoured the system with the “Energy genius 2013” inno­va­tion award. “The ECO part of the name is intended to empha­sise the very best in terms of effi­ciency,” according to Gruber. “We don’t cut any corners when it comes to quality – and that’s what we like about ebm-papst.” The two compa­nies have been working together to their mutual benefit since 2006. And the effort has been well worth­while, as Gruber can confrm: “We do of course have yet more plans in the pipeline in connec­tion with EC tech­nology.”