© Photo | ebm-papst

An effi­cient family

Optimum burning in gas appli­ance requires perfect harmony between the compo­nents. The NRV systems by ebm-papst provide the perfect gas/air mixture.

Whether a classic boiler in a single-family dwelling, a micro CHP for heat and energy gener­a­tion, or the deep fryers in restau­rants for crispy french fries – as different as the func­tions of these devices are, they all have one thing in common: They all use energy produced by burning gas. Compared to other fuels, this process is more effi­cient and produces lower emis­sions.


Figure 1: NRV 77 – The heat output range can be adjusted by the displacer in the venturi.

Gas can only develop these envi­ron­men­tally friendly char­ac­ter­is­tics in an optimum combus­tion process. Achieving the highest energy output is always a chal­lenge for equip­ment manu­fac­turers. The mix ratio, among other things, is crucial. If the concen­tra­tion of gas is too high, not enough oxygen will be avail­able. This is referred to as a “rich mixture”. The result: The gas that is not burned escapes with the fumes, the amount of soot increases, and carbon monoxide is released into the atmos­phere. On the other hand, if the concen­tra­tion of gas is too low, the flame will be extin­guished in the burner. Further­more, not all gases are alike. There are many different types of gas, with different compo­si­tions and energy contents, depending on where they are extracted. There­fore the gas flowing through the supply grid varies from region to region. For the best mixture, these factors have to be consid­ered.

Perfectly harmo­nized


Figure 2: Water heater kit consisting of NRV 118 and burner controller.

The mixture prepa­ra­tion plays an impor­tant role in devices that use gas as an energy carrier. The unit consists essen­tially of three compo­nents: a blower, a venturi mixing device, and a valve. In order to achieve perfect harmony, ebm-papst in Land­shut has combined these three compo­nents into a so-called “NRV system”. All versions of the system are built according to the same prin­ciple. In the venturi, fresh air flows through a tapered nozzle. This produces a vacuum at the narrowest point that causes the gas to be pulled through the valve. It is attached to the side of the venturi, and – in the so-called pneu­matic combus­tion system – regu­lates the amount of gas that may actu­ally flow out. The blower is respon­sible for a homo­ge­neous gas/air mixture and conveys it to the burner. As an option, ebm-papst also offers the appro­priate burner control unit that moni­tors gas safety and controls the heat output for this system. Thus, customers receive a complete system perfectly matched to their require­ments.

Indi­vidual solu­tion


Figure 3: iNR77: The elec­tronic system with inte­grated gas valve covers a power range up to 35 kilo­watts, but is avail­able only project-specif­i­cally.

Currently the NRV family includes four different systems with different blower sizes: NRV 77, 118, 137 and 148. They cover different power ranges, and all have a turn down ratio of at least 1:5. Depending on the model, even a ratio of 1:10 is possible. The specific para­meter indi­cates the ratio between the possible minimum and maximum power output of the heating unit. The greater the modu­la­tion range, the better the power can be adapted to the actual need. This enables effi­cient combus­tion even in low power ranges. The power ranges in the NRV systems can be modi­fied to allow for the best possible adap­ta­tion. This is made possible by the multi­ven­turis devel­oped espe­cially by ebm-papst. Here, a displacer located in the plastic tool is used to vary the cross section of the venturi (figure 1). For example, for the NRV 77 three different venturi elements can realize 2 to 15, 5.5 to 28, and 7 to 35 kilo­watts, thus enabling indi­vidual adjust­ments for small quan­ti­ties without addi­tional costs.

Compact construc­tion


Figure 4: Appli­ca­tion of the NRV system using the example of the wall-mounted gas heater.

One thing that all NRV systems have in common is their compact design. Due to the modular struc­ture, they can be adapted easily to the space require­ment of the respec­tive customer appli­ance. This allows different instal­la­tion posi­tions. Further flex­i­bility is given by the possi­bility to adjust the mounting posi­tions of the multi­ven­turi and the valve. Adjustable mounting clips make it possible to mount the burner control unit directly on the assembly (figure 2) without any further adjust­ments. But it can also be installed sepa­rately from the system.

The elec­tron­i­cally controlled combus­tion system: iNR77

With the iNR77, compo­nent inte­gra­tion has been taken to the next level. In this elec­tronic system, a mass flow sensor measures the air flow supplied to the burner. Based on this infor­ma­tion, the blower motor is controlled specif­i­cally to generate the optimum gas/air mixture. The iNR77 requires signif­i­cantly less space because the elec­tronic gas valve is inte­grated directly in the blower housing (figure 3). In the company’s own gas labo­ra­tory in Land­shut, the engi­neers are able to adjust the systems to the specific needs of the customers. This means a very effi­cient proce­dure in the devel­op­ment process together with the customers, and the produc­tion of opti­mally adjusted, envi­ron­men­tally friendly, and energy-effi­cient devices (figure 4).

Diverse appli­ca­tions

The NRV systems can be used in the following appli­ca­tions:

  • Gas-condensing boilers for house­holds or commer­cial appli­ca­tions
  • Air and water heaters
  • Humid­i­fiers
  • Restau­rant equip­ment such as gas-oper­ated deep fryers or stoves
  • Fuel cells


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