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.