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Compact, quiet and reli­able

Induced draft fans for opti­mised biomass heating

Econom­ical heating, envi­ron­men­tally friendly combus­tion tech­nology and conve­nient oper­a­tion are the main require­ments for heating systems in private homes today, so systems using wood pellets, wood chips and split logs are used in a variety of situ­a­tions. They can be used within living areas or for central heating in single- or multi-family homes as well as public build­ings. Compact dimen­sions and quiet oper­a­tion are impor­tant consid­er­a­tions. After all, nobody wants envi­ron­men­tally friendly heating to come at the expense of living comfort. Fans for fresh air and exhaust gases play an impor­tant role here and need to deliver convincing perfor­mance in terms of energy effi­ciency, noise, reli­a­bility and compact­ness.

Figure 1: Schematic diagram showing oper­a­tion of a biomass solid fuel heating unit with speed-controlled induced draft fan assisting the flue draft for optimum combus­tion

Modern biomass heating systems are enjoying increasing popu­larity. They can be oper­ated with pellets, wood chips or split logs – renew­able energy sources with carbon-neutral combus­tion. Such systems are compa­rable to oil and gas systems in terms of oper­a­tion and main­te­nance. They have low emis­sions and reach effi­cien­cies of over 90% (even as much as 105% Hi for condensing boilers). To opti­mise the effi­ciency while minimising the pollu­tant content of the exhaust gases, modern systems control the combus­tion process with either a temper­a­ture or combus­tion chamber sensor or a lambda probe, typi­cally in combi­na­tion with an induced draft fan (Figure 1). The fan’s speed is controlled based on the measured values or in accor­dance with a specific set of para­me­ters to ensure an appro­priate flue draft, so the fan makes an essen­tial contri­bu­tion to clean, high-quality combus­tion.

External rotor design for compact dimen­sions

Figure 2: New-gener­a­tion induced draft fan with energy-effi­cient EC tech­nology

The demands placed on induced draft fans are partic­u­larly high. They have to with­stand high temper­a­tures and be quiet, energy-effi­cient and easy to inte­grate. This is partic­u­larly the case when they are used in heating systems for living areas, but even when they are installed in central heating systems, induced draft fans should take up as little space as possible.
For the latest gener­a­tion (Fig. 2) of induced draft fans, the motor and fan specialist ebm-papst Mulfingen employs the proven external rotor design. Here the static part of the motor, the stator, is located on the inside and is surrounded by the rotating part, the rotor. Simply by using this config­u­ra­tion, a higher torque can be achieved than with an internal rotor motor of the same length and using the same magnet system. So for a given output, external rotor motors can be much more compact. In combi­na­tion with the fan, the result is a compact unit that is also rugged and durable.

AC or EC motor?

Figure 3: Mechan­ical design of external rotor motor, with commu­ta­tion elec­tronics situ­ated in the cool region at a distance from the combus­tion chamber

For the new induced draft fans, users can choose between conven­tional asyn­chro­nous (AC) motors and elec­tron­i­cally commu­tated (EC) synchro­nous motors. However, for controlled fans the choice will nearly always be in favour of the energy-saving EC tech­nology. For asyn­chro­nous motors, the maximum speed is limited by the mains frequency. The rotor speed adapts to the rotating field frequency via slip depending on the load situ­a­tion. As an alter­na­tive, speed control via frequency change or phase control is also possible. However, this requires external control elec­tronics and an addi­tional Hall sensor in the motor for speed measure­ment. Since the effi­ciency of AC motors decreases sharply in closed-loop oper­a­tion, much more effi­cient induced draft fans can be produced using EC motors. EC fans consume up to 70% less energy in partial-load oper­a­tion, resulting in reduced oper­ating costs and envi­ron­mental impact and making energy-saving fans and envi­ron­men­tally friendly heating an excel­lent combi­na­tion.

EC tech­nology: energy-effi­cient and quiet

Figure 4: EC fans are much more effi­cient than conven­tional AC designs, espe­cially in the partial-load range

In an EC motor, the rotor with its perma­nent magnets rotates synchro­nously with the stator’s rotating field (Figure 3). In contrast to the mains-powered asyn­chro­nous motor, the rotor speed is not auto­mat­i­cally coupled to the frequency of the supply voltage but is pre-deter­mined by the commu­ta­tion elec­tronics, which deter­mine the angular speed of the stator rotating field with which the rotor synchro­nously rotates.
The commu­ta­tion elec­tronics deter­mine the rotor posi­tion in part without sensors by using the para­me­ters rotor voltage or motor current. The idle speed depends on the applied voltage and the number of turns in the stator winding, making nearly any oper­ating speed possible without slip (synchro­nously with the stator’s rotating field) and, in contrast to the mains-powered asyn­chro­nous motor, even above the mains frequency. In addi­tion, the minimum speed that can be reached with an EC motor is lower than that for an AC motor. So the speed can always be adjusted over a wider control range to meet current require­ments. Further­more, in partial-load oper­a­tion in partic­ular but at full load as well, EC motors are consid­er­ably more effi­cient than mains-powered AC motors (Figure 4) and are very quiet in compar­ison with speed-controlled asyn­chro­nous motors, whose triac controllers can cause objec­tion­able noise.

New mechan­ical design with extra bene­fits

Figure 5: Modular design of the new induced draft fans: Both an elec­tron­i­cally commu­tated (EC) synchro­nous motor with direct mains supply or direct current (DC) supply and a conven­tional AC motor with the same dimen­sions can be used

Mechan­i­cally, the new induced draft fans feature a modular design that permits the use of both conven­tional AC and energy-effi­cient EC motors with iden­tical external dimen­sions (Figure 5). The EC motor was designed so that the elec­tronics inte­grated in the motor are situ­ated in the cool region as far as possible from the hot combus­tion chamber to protect the elec­tronic compo­nents from the unavoid­ably high temper­a­tures there. The insu­lated, customer-specific mounting plate with adja­cent cooling wheel also helps to protect the elec­tronics. Long-term testing has confirmed that temper­a­tures of 250 °C have no detri­mental effect on func­tion­ality over time; the induced draft fans are even designed for brief temper­a­ture peaks up to 300 °C. The stain­less steel impellers are avail­able in different designs with diam­e­ters from 120 mm to 250 mm. An optional shaft seal devel­oped for these fans prevents flue gas from leaking through the shaft gap. This is impor­tant since venti­lation systems in living areas can cause under­pres­sure which results in flue gas being sucked into the room. Sealed stoves with an external air supply are manda­tory here.
The mechan­ical design has further advan­tages. The induced draft fan’s hood is made of a very tough, temper­a­ture-resis­tant and flame-proof fibre­glass-rein­forced plastic mate­rial. The fan’s torsion-resis­tant hollow ribs provide a sturdy support struc­ture. If an AC motor is used, the terminal box can simply be fastened to the hood. For appli­ca­tions with an existing external power supply, low-voltage DC motors with the same perfor­mance data and an iden­tical design will be avail­able in future.

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  • kindly tell me about your local dealer in India near by new delhi

    • klindner on said:

      Dear Saudan,

      Thank you for your inquiry. Our only subsidiary in India is located in Chennai

      ebm-papst India Pvt. Ltd.
      26/3, G.N.T. Road Erukkencherry
      600 118 Chennai
      Telefon: +91 44 26720103
      Telefax: +91 44 25371149

      Best regards, your mag°Team

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