Fans in cooling towers are respon­sible for effi­ciently dissi­pating heat to the envi­ron­ment; in partic­ular, heat gener­ated when a process, system or building is cooled using water (cover picture). At the same time, the fans that are used must be extremely rugged because they have to with­stand high humidity levels, various envi­ron­mental influ­ences and rapid changes in temper­a­ture. And last but not least, they must be as quiet as possible – partic­u­larly if the cooling towers are located near resi­den­tial areas or mixed-use zones.

Several smaller fans provide bene­fits: flex­ibly arranged for a compact design and consis­tant air distri­b­u­tion.

More fans, more bene­fits

With conven­tion­ally struc­tured cooling towers, it is becoming more and more diffi­cult to satisfy these require­ments completely. In order to generate high air flow, very large fans are typi­cally used. They are driven by trans­mis­sions or belts from an AC motor. Due to the weight of the large single fans, they have a solid design and cannot be installed until they reach the construc­tion site. This makes it virtu­ally impos­sible to precisely balance the rotating impeller, which frequently leads to prema­ture fail­ures in oper­a­tion. Such fans often run in two-phase, star/delta or on/off oper­a­tion.

In addi­tion, the corners of the cooling tower do not have uniform through-flow and the towers also end up being very high because to achieve even through-flow, there must be a large space between the fan and the heat exchanger nozzles. The ebm-papst approach includes replacing the large fan with several smaller fans running in parallel oper­a­tion (a FanGrid), which trans­lates into several bene­fits in prac­tice.

 

 

The indi­vidual fans can be stacked or arranged in rows to use the avail­able space to maximum advan­tage (Fig. 2). Due to the fans’ small diam­e­ters, cooling towers can be built more compactly and depending on the floor space, have a rectan­gular or square cross-section. Smaller fans are easier to handle than one large fan. The latter benefit makes trans­port and instal­la­tion easier, but is also a major advan­tage when replacing the fans.

ebm-papst provides FanGrid fans for cooling towers in axial or centrifugal design, for example.

And until a fan is replaced, the cooling tower can operate normally. The speed of the other fans is simply adjusted to main­tain constant air perfor­mance. During the design process, the rele­vant redun­dancy require­ments can be taken into account. In addi­tion, the air distri­b­u­tion is much more even when several fans are used (Fig. 3). Flow-through is more uniform for all compo­nents and disad­van­ta­geous dead zone are reduced.

 

 

Today, the bene­fits of a FanGrid can be lever­aged in a wide range of appli­ca­tions. Motor and fan specialist ebm-papst provides FanGrid fans for cooling towers in axial or centrifugal design, for example (see Fig. 4). This means that different require­ments for pres­sure increase and air flow can be satis­fied.

Axial fans show their strengths when high air flow and moderate pres­sure increase are required: for inlet oper­a­tion, for example. Centrifugal fans are designed for high back pres­sure and are recom­mended for pres­sure oper­a­tion. A wide range of sizes with a variety of diam­e­ters is also avail­able.

ebm-papst has a flex­ible selec­tion tool to help customers find the optimal combi­na­tion of fans for a wide range of appli­ca­tions: the ebm-papst FanScout (Fig. 5). Based on up to five appli­ca­tion-specific oper­ating points and the antic­i­pated oper­ating times, this soft­ware deter­mines the most effi­cient FanGrid solu­tion. The amount of instal­la­tion space avail­able, maximum number of fans required and redun­dancy require­ments can also be taken into account.

ebm-papst FanSout is a flex­ible selec­tion tool helping to find the optimal combi­na­tion of fans.

And there is also an option to deter­mine the life cycle costs of the best combi­na­tion. In this way, users receive a reli­able, robust cost break­down upon which they can base their invest­ment and modern­iza­tion deci­sions.

EC tech­nology: energy effi­cient and quiet

The driving force behind cooling tower fans are modern Green­Tech EC drives that func­tion highly energy effi­ciently in full and partial-load oper­a­tion, are designed for long service lives and feature infi­nitely vari­able speed control. This ensures a constant air perfor­mance under all condi­tions. With over 90% effi­ciency, the motors deliver much more than the values required in effi­ciency class IE4. The flow machine design also contributes to increased effi­ciency and quiet oper­a­tion. Prob­lems due to noise protec­tion regu­la­tions are a thing of the past.

An example appli­ca­tion shows that the energy savings pay in prac­tice. Instead of one large fan with a diam­eter of 2,100 mm, four axial fans with a diam­eter of 910 mm each were installed in a cooling tower to generate the same air flow of 87,040 m³/h at a static pres­sure of 100 Pa. This enabled power consump­tion to drop from 7.8 kW to just under 5.3 kW (four times 1.32 kW). In total, the retrofit meant annual energy savings of almost 22,000 kWh for the oper­ator.

 

 

For rota­tion moni­toring, the fans can be contin­u­ously moni­tored via an ebm-papst cloud connec­tion. In the process, internal measured values such as speed, motor temper­a­ture and vibra­tion values are read out and trans­mitted to the ebm-papst cloud. Users always have an eye on the FanGrid fans and if neces­sary, can plan preven­tive main­te­nance on their cooling towers.

Success­fully tested under extreme condi­tions

To with­stand the high humidity and rapid changes in temper­a­ture common for use in cooling towers, the fans have extremely rugged designs. All compo­nents are protected by special coat­ings. The fan series have proven their resis­tance under extreme test condi­tions. Salt spray tests, vibra­tion and shock tests, and propri­etary corro­sion and mois­ture tests were used for qual­i­fi­ca­tion. ebm-papst created a custom envi­ron­mental clas­si­fi­ca­tion, H2+C, for its tests. And ebm-papst EC fans have reli­ably performed their func­tion in cooling towers for years.