No alter­na­tive to energy-effi­cient fans

In the latest version of the German Energy Savings Ordi­nance (EnEv) of 2009, the German federal govern­ment reduced the maximum permis­sible energy require­ment for new build­ings by 30% compared to the EnEv of 2007. In the next step, energy stip­u­la­tions are set to become stricter by a further 30% in 2012. These targets will also apply to reno­va­tions. This will make heating systems employing renew­able ener­gies and home venti­la­tion systems that extract heat from the exhaust air to heat up the fresh air indis­pens­able. At the same time, the energy effi­ciency stan­dards expected of such solu­tions are very high, which in turn has an effect on the compo­nents employed. This also affects fans, which already have to satisfy very high stan­dards with respect to effi­ciency.

Natu­rally, imple­menting the required energy effi­ciency means higher costs for the home builder, regard­less of whether it is a new building or a reno­va­tion. However, “envi­ron­men­tally compat­ible” does not neces­sarily have to mean “expen­sive” in the long run. Firstly, the finan­cial “energy-saving premium” will in time pay for itself – regard­less of future energy prices. Secondly, state subsidy schemes relieve the finan­cial burden. Builders of new build­ings can take advan­tage of loans from the KfW (the German state banking group for recon­struc­tion), whose interest rates and possible repay­ment subsi­dies depend on the level of effi­ciency achieved. If you wish to reno­vate an existing building, you have the choice of a wide range of subsidi­s­a­tion stan­dards. Even if the current subsidy schemes fall victim to future cutbacks, the energy saving measures are still worth­while for both new build­ings and reno­va­tions, and not just for envi­ron­mental reasons. Good insu­la­tion and venti­la­tion enhances the general comfort of the house, and the increase in the value of the prop­erty should also not be neglected.

The deci­sive compo­nent: the fan

Home venti­la­tion systems with heat recovery are espe­cially suit­able for low-energy and passive houses, but they are also employed in the reno­va­tion of older build­ings. For apart­ments and single-family homes, central systems are usually employed (see box text). Here, the fresh air and the exhaust air are conveyed through ducts by two fans. Heat recovery and air filtra­tion are managed by the central unit, which can be placed prac­ti­cally anywhere, e.g. in the cellar.

The fans for the fresh air and exhaust air form the “heart” of the system. They are required to work reli­ably and energy-effi­ciently as such venti­la­tion systems are usually in contin­uous oper­a­tion. More­over, it is essen­tial for low-noise and low-vibra­tion motors and fans to be used. Because the venti­la­tion ducts are routed throughout the building, droning motors would cause signif­i­cant noise distur­bance. At the end of the day, nobody wants to hear a thing from the venti­la­tion.

The right drive: unbeat­able EC tech­nology

The drive employed is a key crite­rion when selecting the right fan. Today, “asyn­chro­nous motors” are still employed to drive fans in venti­la­tion and climate control systems. These AC motors are of a straight­for­ward design and are powered directly from the A/C or three-phase current supply. Neither mechan­ical collec­tors nor elec­tronics are needed to power the arma­ture. They are robust and reli­able, but they have one deci­sive draw­back: depending on the design, the are only able to achieve an effi­ciency rating of about 50%. The effi­ciency describes the rela­tion­ship between the achieved mechan­ical output and the elec­trical input. In other words, it is a measure of the energy effi­ciency of a drive. Modern EC drives, specially devel­oped by motor and fan specialist ebm-papst for use in home venti­la­tion systems, perform substan­tially better in this respect, which is due to the way they work.

On the EC motor, a magnetic rotor synchro­nously follows an elec­tron­i­cally gener­ated rotating field. EC motors are direct current motors that are straight­for­ward to control. They work with an effi­ciency of up to 90%. Oper­ating costs are reduced, the climate control solu­tion pays for itself rela­tively quickly and signif­i­cantly less CO2 is created from the very first minute of oper­a­tion, reducing the impact on the envi­ron­ment. At the same time, the drives are also remark­ably quiet. The key to this is the espe­cially low-noise commu­ta­tion.

The right blade geom­etry

Apart from the motor, the geom­etry of the blades is an impor­tant factor when choosing the right fan. For home venti­la­tion systems, centrifugal fans are employed, where a distinc­tion has to be made between forward and back­ward curved blades. In home venti­la­tion systems, forward curved centrifugal fans are predom­i­nantly employed. Here, the rela­tion­ship between the power input, speed and air flow is approx­i­mately linear. That means that the air flow can be calcu­lated using the speed and current draw, and the air flow can be controlled without an air volume sensor. The elec­tronics inte­grated in the EC motor takes care of these addi­tional control func­tions. The sensor­less air flow control also creates further advan­tages. This means that there is no reduc­tion in air flow caused by cont­a­m­i­nated filters. More­over, the regu­la­tion of the air flow is more straight­for­ward when the system is set up, which is an addi­tional cost factor that should not be under­es­ti­mated.

“Tailor-made” solu­tions for different appli­ca­tions

Because the neces­sary air flow depends on the size of the space to be venti­lated, there are different centrifugal fans avail­able with Green­Tech EC tech­nology for air flows of up to 180 m³/h, 300 m³/h and 400 m³/h. These fans are housed in a compact scroll housing and are directly connected to the 230V AC voltage supply with a frequency of either 50 or 60 Hz. The required air flow can be set using either a pulse width modu­la­tion signal or a vari­able voltage between 0 and 10 V.

The speed moni­toring func­tion inte­grated into the motor elec­tronics emits one pulse per revo­lu­tion. Various devices can be connected to this output, for example a counter, controller, alarm trans­mitter or a speed indi­cator. There is no need for a anti-vibra­tion mount as the three-core design of the EC drive and the opti­mised commu­ta­tion tech­nique prevent motor noises from being gener­ated. These advan­tages can of course also benefit decen­tral­ized venti­la­tion systems. Here, there is also a wide range of powerful fans that combine energy-effi­cient EC tech­nology with quiet running and a range of prac­tical control and regu­la­tion options.

Another inter­esting appli­ca­tion for effi­cient fans is in heat pumps (air/water and air/air). These are often combined with central venti­la­tion systems, espe­cially in low-energy houses. In such combined solu­tions, the two fans in the venti­la­tion system are supple­mented by another one for the heat pump. The “RadiCal” centrifugal fan range employs Green­Tech EC tech­nology and is very well suited to this appli­ca­tion. Not only are these fans extremely energy-effi­cient, they are also very quiet. The fans are currently avail­able in sizes 133 mm to 250 mm with drive power between 35 and 170 W, and in size 500 mm with three different EC motors with drive power 500 W, 1 kW and 3 kW. This fan range also helps to ensure not only that the energy savings that are stip­u­lated by law are achieved, but also that they are econom­ical for the user.

Central­ized or decen­tral­ized?

When it comes to climate control in build­ings, plan­ners and oper­a­tors have the choice between central­ized and decen­tral­ized solu­tions. The market used to be domi­nated by central­ized air-condi­tioning systems. Today, decen­tral­ized solu­tions for indi­vidual rooms or for smaller units are becoming increas­ingly popular as they allow indi­vidual adap­ta­tions to suit the needs of the user and detailed indi­vidual invoicing. These units are inte­grated directly on the facade of the building and they do not need a ducting system for the fresh air and exhaust air. This makes them perfect when reno­vating existing build­ings. However, heat recovery and air filtra­tion are more straight­for­ward and more effi­cient with centralised systems, and main­te­nance work is easier to schedule and perform. This usually makes then the better option for single-family homes or multi-storey apart­ments.