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Change is in the air for furni­ture store: Retrofit with a FanGrid

Completely replacing old venti­lation systems is time-consuming and costly. The retrofit project at a large furni­ture store in Dubai shows that there is a better solu­tion: EC fans in the form of a FanGrid and demand-based control.

Fig. 1: The old, belt-driven fan was much more diffi­cult to remove from the AHU due to its size and weight. Instal­la­tion of the new solu­tion there­fore had to be carried out even faster. (Photo | ebm-papst)

Two air handling units (AHUs) supply a large furni­ture store, including a ware­house, in Dubai with fresh, cooled air. Belt-driven AC fans were used for this (Fig. 1). The control concept imple­mented on site allowed for one of the two AHUs to always be in oper­a­tion at full load for six months, while the other AHU was out of service at the same time. After six months, the other AHU took over the supply of fresh air again. Since the AC fans could only ever operate at a single speed, a lot of energy was wasted, above all when there were few people in the furni­ture store, as more fresh air was supplied than required.

There was only one solu­tion that could be imple­mented both econom­i­cally and within the required time for these prob­lems. This was equip­ping the AHUs with new, effi­cient fans and opti­mizing the control system in line with require­ments. Jon Davies was awarded the retrofit with his company Qey Energy Solu­tions, which has its head­quar­ters in Dubai. In this project, they collab­o­rated with Johnson Controls to develop a suit­able control concept.

A complete solu­tion for the AHUs

There are gener­ally two chal­lenges for retro­fits: time and space. This was also the case in this project. Qey calcu­lated four days for the conver­sion of an AHU. If the other unit failed during this time, there would be no more fresh air supply for the furni­ture store. This time pres­sure meant that the new fans needed to be installed quickly and smoothly. The new solu­tion thus had to be installed in the AHU so it saved space and was as ready in advance as it could be.

This is why the “MatrixAir+ EC” fan package from Qey was used. This complete solu­tion consists of four prod­ucts: EC fans, fan connec­tion boxes, fan bulk­heads, and control panels. For the first compo­nent, EC centrifugal fans from the RadiPac series from ebm-papst (Fig. 2) were chosen, as their compact design and ready-to-install plug-&-play design make them easy to install. A total of 26 Radi­Pacs were installed as FanGrids in the AHU intake and exhaust sections.

Fig. 2: The RadiPac series EC centrifugal fans from ebm-papst were chosen. (Photo | ebm-papst)

FanGrid ensures oper­a­tional reli­a­bility

A FanGrid consists of several small fans arranged next to or above one another and oper­ated in parallel (Fig. 3). The redun­dant design increases the reli­a­bility of the entire system and ensures oper­a­tional reli­a­bility. If one fan fails, the other EC fans compen­sate for the missing air volume. Even if an entire AHU fails, the remaining AHU is still able to inde­pen­dently meet the complete fresh air require­ments.

Fig. 3: In each box, there is an EC centrifugal fan from the RadiPac series that together form the FanGrid. This design ensures partic­u­larly high oper­a­tional reli­a­bility. (Photo | ebm-papst)

This offers the neces­sary reli­a­bility, partic­u­larly in large plants and espe­cially hot regions like Dubai. In addi­tion, it is no longer neces­sary to operate an AHU constantly at full load while the second serves as a back-up. The current fresh air require­ments are distrib­uted evenly across both AHUs (Fig. 4).

The fans are oper­ated at partial load, which has a posi­tive effect on the service life. Another advan­tage of this type of setup is that the flow through upstream and down­stream compo­nents, such as filters or heat exchangers, is more uniform. This results in more effi­cient filtering of the air, as well as better heat transfer perfor­mance, and thus a reduc­tion in oper­ating costs. Several small fans may also require less space and are lighter than one large fan, making replace­ment easier.

EC motor saves energy

The main aim of the retrofit was to save energy. This can be achieved through two mutu­ally bene­fi­cial measures: replacing the fans and reworking the control system. Those involved in the project in Dubai decided on both to exploit the greatest possible energy saving poten­tial. Signif­i­cant savings are already possible thanks to the high effi­ciency of Green­Tech EC motors of over 90% alone.

Fig. 4: The current fresh air require­ments are distrib­uted evenly across both AHUs, which improoves their life­time. (Photo | ebm-papst)

They are also infi­nitely adjustable, ensuring demand-based oper­a­tion – so between 0 and one hundred percent instead of just on and off as is the case with AC fans. This results in signif­i­cant savings poten­tial, as the power consump­tion increases or falls in line with the speed to the power of three (P~n³). This means that if the speed is reduced by half compared to the nominal speed, the required power consump­tion is reduced by a factor of 8 and is there­fore only 12.5% of the rated output.

However, if half of the number of AC fans is switched off and the other half still oper­ates at full load, only 50% of the power consump­tion can be saved. The reduc­tion in speed also leads to signif­i­cant advan­tages in terms of noise emis­sions. Thanks to the wide optimum effi­ciency range of centrifugal fans, they work with as little power consump­tion as possible at just about every oper­ating point.

Demand-based control

After replacing the fans, they moved onto the control system (Fig. 5). The furni­ture store’s venti­lation system already had a building manage­ment system, but the aim was to develop a time-based strategy. For this purpose, occu­pancy data was eval­u­ated, the number of visi­tors (which varies throughout the day) calcu­lated, and the asso­ci­ated air flow require­ments deter­mined depending on the time.

Fig. 5: In addi­tion to replacing the fans, a modern, demand-based control system also plays a major role in saving energy. (Photo | ebm-papst)

This data was then used to program the “Sched­uled Mode,” in which a controller spec­i­fies the fan speed at certain times based on an internal schedule. Both AHU controls work in parallel to always convey 50% of the required air flow depending on time. A prereq­ui­site for the control system was also that the fans could commu­ni­cate with the building manage­ment system. Thanks to the inte­grated control elec­tronics of the RadiPac EC fans with RS485/MODBUS RTU inter­face, this was no problem.

What the Tech: How will a retrofit increase the effi­ciency and dura­bility of your venti­lation unit?

What is a Retrofit? And why could it be the right choice for me?

Find the answer here: simple, under­stand­able and with a bit of humor!

Commu­ni­cating with the building manage­ment system was partic­u­larly impor­tant for docu­menting oper­ating data. Firstly, this enables the actual savings to be checked and, secondly, the control system to be opti­mized. If you eval­uate data, you have more reli­a­bility as prob­lems can be iden­ti­fied quickly and nega­tive conse­quences can be prevented at an early stage.

A differ­en­tial pres­sure measure­ment is easy with the RadiPac, as it has a pres­sure tap for connecting a differ­en­tial pres­sure trans­mitter. This enables conclu­sions to be drawn about the conveyed air flow, and this can be moni­tored along­side many other impor­tant fan oper­ating data. This also makes it possible to deter­mine the savings resulting from the retrofit. In this case, an impres­sive 79%. The Qey project team also expects a return of invest­ment of just 3 years.

The 5 most common ques­tions about retro­fitting

1. When is a retrofit worth­while?

If a venti­lation system is 10, 15 years or older, an upgrade makes sense in many cases. Switching to new EC fans saves a signif­i­cant amount of energy. Other advan­tages include dura­bility, saving space, and oper­a­tional reli­a­bility.

2. How do I approach a retrofit?

Retrofit experts provide support in recording perfor­mance data, work out possible concepts, and can provide a rough overview of costs. They look at the purpose of the system and at which point it should be oper­ated opti­mally.

3. How does a retrofit work?

The first step is a current measure­ment of the current status. Then it is time to select the right fan. In this process, the entire system, envi­ron­mental factors (alti­tude, temper­a­ture, etc.), options for elec­trical inte­gra­tion, and mains supply must be taken into account. During instal­la­tion, atten­tion must be paid to the seals in the venti­lation room. The new state is then measured at the end.

4. What payback period can I expect?

This cannot be answered on a general basis, as the local energy costs are a signif­i­cant factor. But even with the low energy costs in the United Arab Emirates (compared to the situ­a­tion in Germany, for example), it was possible to achieve a short payback period of just 3 years due to the great savings achieved.

5.How do these savings come about?

Thanks to the EC tech­nology, opti­mized aero­dy­namics, and demand-based speed control.

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