When it comes to a carbon-neutral future, most people talk about solar energy or wind energy. But there is another sector here that uses a lot of energy and has a nega­tive impact on the global carbon foot­print: heating. In Germany alone, this item accounts for more than 25 percent of total energy consump­tion; in private house­holds, the share is even 90 percent. In addi­tion, around 12 million heating systems are older than ten years in this country alone, and these there­fore often have an unsat­is­fac­tory energy foot­print. From a global perspec­tive, the need to catch up is most likely even greater. In other words, if the energy revo­lu­tion is to succeed, we need a heating revo­lu­tion. The now well estab­lished energy-effi­cient gas-condensing tech­nology, which has been contin­u­ously devel­oped and refined over the past 20 years, makes an impor­tant contri­bu­tion to this.

Combus­tion is crucial to the effi­ciency of these condensing units. The energy yield is only perfect with an optimum mixture ratio of air and gas. An exces­sive propor­tion of gas leads to harmful emis­sions such as soot and carbon monoxide, for example, and too much air reduces the effi­ciency of the combus­tion. It is there­fore crucial that the compo­nents of the gas-air composite system are perfectly matched. In this regard, pneu­matic combus­tion control has proven itself in prac­tice for years. As a future-proof alter­na­tive, the elec­tronic combus­tion control system is added to this. In the long term, it may even replace its pneu­matic sister. Until then, however, both systems will run in parallel on the market. ebm-papst offers both vari­ants as a complete solu­tion for use in condensing units in resi­den­tial build­ings up to 150 kW: CleanEco (pneu­matic) and Clean­Vario (elec­tronic).

Figure 1: Func­tional diagram of CleanEco pneu­matic combus­tion control. (Graphic | ebm-papst)

CleanEco: robust and tried-and-tested

The CleanEco pneu­matic composite system consists of a blower, venturi, gas valve, and the control unit (boiler control unit – BCU (Fig. 1). The prin­ciple: The blower draws in the air, a vacuum is created by the tapering of the venturi, which controls the gas supply via the valve. When correctly adjusted, this results in the optimum mixture of oxygen and fuel. The gas-air mixture remains stable regard­less of coun­ter­pres­sure and changed exhaust gas resis­tance. Over the years, the engi­neers at ebm-papst have opti­mized the system so that modu­la­tion levels of 1:10 are now possible, meaning the output of the boiler adapts much more precisely to the demand actu­ally required. But even though the pneu­matic composite system is tried and tested and robust, it depends on a constant gas quality, as the valve is precisely set to the rele­vant type of gas fed in at the site of the instal­la­tion.

Clean­Vario: a flex­ible system

Figure 2: Clean­Vario elec­tronic combus­tion control. (Graphic | ebm-papst)

And it is precisely here that a major change is happening. Looking at Europe makes this clear. Large gas fields, such as in the Nether­lands, are almost depleted and new sources need to be found. This also includes alter­na­tive fuels. In addi­tion to natural gas, in future hydrogen, liquid gas, or biomethane from power-to-gas plants will also flow through the pipes. This means that the condensing units of the future will have to react flex­ibly and have to deliver constant perfor­mance despite these fluc­tu­a­tions. A system is there­fore required that is gas adap­tive. The answer to this chal­lenge already exists: the elec­tronic gas-air composite system which goes by the name Clean­Vario at ebm-papst (Fig. 2).

When looking at the compo­nents, there is initially no major differ­ence. There is still a blower, venturi, control unit, and gas valve here, but their inter­ac­tion is different (Fig. 3). The mixing ratio is not controlled here by the vacuum but by elec­tronic actu­a­tion of the gas valve. The gas valves in Clean­Vario there­fore have a stepper motor which is used to regu­late the feed precisely. But to ensure that the valve knows how much gas it is to provide for mixing with the air, it requires a para­meter that signals when the mixture is perfect. In theory, the ideal mixture of fuel and air for complete combus­tion is a combus­tion ratio of λ = 1. If the value is below one, the oxygen content is too low; if it is greater, then it is too high. But how do you measure whether the combus­tion is running opti­mally? The best way is the flame itself.

Figure 3: Func­tional diagram of Clean­Vario elec­tronic combus­tion. (Graphic | ebm-papst)

The flame is crucial

For Clean­Vario, ebm-papst relies on so-called ioniza­tion tech­nology. This utilizes the fact that the flame is elec­tri­cally conduc­tive. If a voltage is applied, an elec­trode can measure the so-called ioniza­tion current directly on the flame. This can be used to draw conclu­sions about the combus­tion quality. If the current is too weak, the valve receives the signal to supply more gas; if it is too high, it restricts it (see gallery below).

This enables the combus­tion to be controlled inde­pen­dently of the fuel. The system can thus auto­mat­i­cally adjust to the gas type without any changes to the valve, and provide clean combus­tion. This now also works if up to 30 percent hydrogen is added. However, the major chal­lenge here is to measure the ioniza­tion current precisely, as it is in the microam­pere range. The devel­opers at ebm-papst have there­fore put a lot of exper­tise into the flame ampli­fier, which, as its name suggests, strengthens the signals received by the sensor. It is impor­tant that inter­fer­ence signals, such as mains hum, are filtered out in the process.

During combus­tion, elec­trons are released. If you apply the elec­tric voltage U, an elec­tric current I flows through the flame – the “ioniza­tion current”. The level of current depends on the combus­tion. (Graphic | ebm-papst)

The ioniza­tion signal is at its highest with complete combus­tion, i.e. at a combus­tion air ratio of λ = 1. Auto­matic cali­bra­tion deter­mines the ioniza­tion value for the desired air ratio range. (Graphic | ebm-papst)

The data obtained goes to the boiler control unit, which controls the blower and the valve according to the required combus­tion power. The combus­tion is regu­larly checked by the ioniza­tion current to regu­late the gas flow. (Graphic | ebm-papst)

Intel­li­gence for the future

But without intel­li­gent soft­ware, the data obtained would be worth­less. For both pneu­matic and elec­tronic complete systems from ebm-papst, the intel­li­gence is located in the boiler control unit (BCU), the central control unit. It regu­lates all elec­tronic safety and control func­tions of condensing boilers.

In the case of the Clean­Vario elec­tronic system, it can collect and eval­uate the data obtained from contin­uous combus­tion moni­toring in order to ulti­mately opti­mize the unit‘s oper­a­tion in the sense of a self-learning system, in the spirit of Green­In­tel­li­gence. During the next start, for example, the stored switch-off states can be used to quickly reach optimum start condi­tions. The elec­tronic composite system also offers a major advan­tage in terms of predic­tive main­te­nance, as a lot more infor­ma­tion about oper­a­tion is avail­able. For example, an increas­ingly small flame signal indi­cates that the elec­trode on the flame has to be replaced.

Everyone bene­fits

With Clean­Vario, manu­fac­turers have the greatest possible flex­i­bility. When it comes to boiler design, there is more leeway for devel­opers because the valve can be installed in the unit regard­less of posi­tion. Since the units are gas adap­tive, this is not just an advan­tage with regard to fluc­tu­ating gas char­ac­ter­is­tics. Serving global markets is also much easier, as the gas valve no longer needs to be adapted to the specific condi­tions of the respec­tive country. It is also much easier for installers because they simply have to install the unit without any time-consuming config­u­ra­tion. The end customer ulti­mately has a unit that provides clean and reli­able combus­tion over its entire service life. That just leaves the envi­ron­ment. If modern gas condensing units are used exten­sively, the chances are good that we can meet the set climate objec­tives, too. CleanEco and Clean­Vario can help with this.