Old meets new

In Germany alone, around 5.6 million oil heaters help keep homes warm. Not only do they burn precious fossil fuels, but they also consume huge amounts of elec­tricity. This means that both manu­fac­turers and customers are looking for ever more effi­cient solu­tions. One of them is Matthias Herbst from Wolf GmbH. The company, based in the Bavarian town of Main­burg, is one of the leading providers of air condi­tioning and heating tech­nology. Its COB oil condensing boiler came out on top in a test by German consumer organ­i­sa­tion Stiftung Warentest and Herbst, who is a project manager in the devel­op­ment team, wanted to improve it further.

Just like its gas-powered coun­ter­part, it uses the energy from the water vapour arising from the combus­tion, which other­wise would just go up the chimney and be wasted. “In order to reduce the oil and energy consump­tion even further, we wanted to make it possible for consumers to modu­late the boiler”, says Herbst of the chal­lenge. This allows the boiler to flex­ibly adjust its power to the actual heating require­ments. “In the end, we changed the combus­tion tech­nology so much that it had to be consid­ered as a completely new devel­op­ment.” This devel­op­ment has been on the market since spring 2014 under the desig­na­tion TOB and promises single and multiple-occu­pancy houses energy-effi­cient housing with low levels of hazardous substances. Compared to its two-stage prede­cessor, the new oil condensing boiler can be oper­ated with modu­lated power between 6.6 and 18.6 kilo­watts.

Spray mist with the ideal angle

This is exactly where the problem lay in devel­op­ment. In order to enable flex­ible modu­la­tion, other manu­fac­turers pre-heat the oil and combust the vapour this creates like gas. The disad­van­tage of this is that the oil evap­o­ra­tion process is extremely energy inten­sive. For the devel­opers at Wolf then, this tech­nology did not even come into ques­tion. They preferred to use compressed atom­i­sa­tion for combus­tion, tech­nology that they have been using for over twenty years. “We wanted to retain this proven method”, explains Herbst. In compressed atom­i­sa­tion, a pump compresses oil at high pres­sure through a nozzle, resulting in a spray mist of tiny droplets. This then combusts with the air that is fed in.

“With the BG 43, we were able to go to the limits of the system in terms of speed. Even at 300 rpm it remains stable.”
Matthias Herbst, Devel­op­ment Project Manager at Wolf GmbH

This process is most effi­cient when the spray mist has the given spray angle of the nozzle. This is no problem at the higher power levels. At lower levels, it is more diffi­cult. If the pres­sure falls below a certain level, the spray angle collapses and the droplets are no longer so fine. This cannot be allowed to happen however, if the unit is to remain adjustable. This meant that the limits of the atom­i­sa­tion process had to be expanded. The engi­neers at Wolf GmbH there­fore devel­oped a special air nozzle. It gives the air (and there­fore the spray mist) the push it needs to create the classic spray mist with fine droplets, even at low pres­sure. The only diffi­culty now was finding the right pump. “We needed a pump that would cover the range between 3.5 and 23 bar, as well as the right motor to ensure every­thing ran stably. It wasn’t so easy”, Herbst explains. The motor needed to be able to deal with low and high speeds, as well as fluc­tu­ating torques.

From blower to motor

This is where ebm-papst came in. Just like in the COB, the TOB was also to be fitted with a blower from Land­shut to control the air flow. In one of the discus­sions focussing solely on these compo­nents, Stefan Ober­maier from the sales depart­ment at ebm-papst heard about the prob­lems surrounding the pump and finding a suit­able motor: “Our BG 43 EC motor imme­di­ately sprang to mind.” The drive motor is suit­able for many different appli­ca­tions, although it had never before been used in oil pumps. The deci­sion was, however, quickly taken to try out the effi­cient all-rounder. “With the BG 43, we were able to go to the limits of the system in terms of speed. Even at 300 rpm it remains stable”, says Herbst of the advan­tages and continues: “It also oper­ates very effi­ciently, just like the blower.” The engi­neers adapted the BG 43 further for this appli­ca­tion, discon­necting the circuit board for the control to enable a modular design.