The Swiss Tower is a 40-story high-rise building in Dubai that houses offices and luxury apart­ments (Fig. 1). The building is constantly supplied with fresh, cooled air from a total of four air handling units (AHUs). Each AHU is respon­sible for supplying fresh air to several floors and was previ­ously equipped with belt-driven AC fans. The old systems were always running at full load, and there was no way to regu­late them according to demand, which would have made sense due to the changing occu­pancy of the office spaces. The bottom line was that oper­a­tion was costly and resulted in a high level of energy waste.

Fig. 1: The Swiss Tower in Dubai is an impres­sive high-rise in Dubai. (Fig. | ebm-papst)

For these prob­lems, retro­fitting the AHUs was both the most econom­ical solu­tion and the one that could best be imple­mented in the required time. The main require­ment of the project was to reduce the power consump­tion of the fans and to exploit further energy saving poten­tial by estab­lishing a control system. The upgrade was also intended to extend the service life of the AHUs. The contract for the retrofit was awarded to Jon Davies and his company Qey Energy Solu­tions, which worked closely with ebm-papst Middle East and Taka Solu­tions to develop an effi­cient solu­tion.

An effi­cient complete solu­tion

In order to keep the down­time of the AHUs as short as possible during the retrofit work, they were upgraded one after the other. However, this meant that during the down­time, parts of the building could no longer be supplied with fresh air. This time pres­sure meant that the new fans had to be installed quickly and without compli­ca­tions. Qey’s “MatrixAir+ EC” solu­tion made this possible. This fan package, consisting of EC fans, fan terminal boxes, fan bulk­heads and control panels, was deliv­ered directly to the AHUs as a pre-prepared complete solu­tion and installed.

When it came to the first compo­nent, the choice fell on EC centrifugal fans from ebm-papst’s RadiPac series. Its compact design and low weight compared to a single large AC fan made the replace­ment easy and stress-free, as no heavy equip­ment was needed for instal­la­tion – which saved time and money too. Since the RadiPac is supplied as a plug & play solu­tion, commis­sioning the EC fan is also a quick process. A total of 26 Radi­Pacs were installed as FanGrids in the intake and exhaust sections of each of the four AHUs (Fig. 2).

Fig. 2: Instead of a single fan, FanGrids were installed in the four AHUs. The pre-prepared fan package makes instal­la­tion quick and easy. (Fig. | ebm-papst)

FanGrid ensures oper­a­tional reli­a­bility

A FanGrid consists of several small fans arranged next to or above one another and oper­ated in parallel. This redun­dant design increases the depend­ability of the system and ensures greater oper­a­tional reli­a­bility (Fig. 3). If one fan fails, the other EC fans compen­sate for the missing air volume. This provides the neces­sary reli­a­bility, espe­cially for large systems, and even more so in partic­u­larly hot regions such as Dubai. Another reason for a FanGrid was to extend the system’s service life. This can be achieved by oper­ating several small fans at partial load as required instead of one large fan constantly at full load.

Another advan­tage of this type of setup is that air can flow more evenly through upstream and down­stream compo­nents such as filters and heat exchangers. This results in more effi­cient filtering of the air, as well as better heat transfer perfor­mance – which in turn reduces the oper­ating costs of the system. Several small fans also usually require less instal­la­tion space and are lighter than a single large fan, making replace­ment easier.

Fig. 3: In a FanGrid, the Radi­Pacs are installed next to or above one another and oper­ated in parallel. This ensures partic­u­larly high oper­a­tional reli­a­bility. (Fig. | ebm-papst)

Energy savings with EC tech­nology

The main aim of the retrofit was to save energy, which is why a fan with an EC motor was chosen. Its high motor effi­ciency level of over 90% alone makes large savings possible compared to the AC motor. In addi­tion, with the old AC fans, only two oper­ating levels were possible: either they were off, or they were oper­ated at maximum speed; there was nothing in between due to the lack of control elec­tronics. This means that regard­less of the actual occu­pancy of the building, all systems always ran at full power, even if at certain times it would have been suffi­cient to supply indi­vidual parts of the building with a lower air volume.

By contrast, EC fans can be contin­u­ously controlled between 0 and 100%, meaning that the speed can always be adjusted to meet demand. This results in signif­i­cant poten­tial for savings, as the power consump­tion increases or falls in line with the speed to the power of three (P~n³). So if the speed is reduced by half compared to the nominal speed, the power consump­tion is reduced by a factor of 8 and is there­fore only 12.5 % of the rated output. If, on the other hand, half of the AC fans are switched off and the other half are still oper­ated at full load, only 50% of the power consump­tion can be saved.

Fig. 4: The demand-based control system regu­lates the air volume flow depending on the time. (Fig. | ebm-papst)

Demand-based fresh air supply

The second part of the retrofit involved upgrading the control system. The Swiss Tower already had a building manage­ment system; the aim with regard to the venti­lation systems was now to develop a time-depen­dent strategy for control­ling them. One advan­tage was that, thanks to the secu­rity scans at the entrance and exit, data was already avail­able on the building’s occu­pancy, which varied according to the time of day. Working with Taka Solu­tions, Qey used this data to deter­mine the airflow require­ments on a time-depen­dent basis and programmed an internal schedule using soft­ware devel­oped specif­i­cally for retrofit projects (Fig. 4).

Office occu­pancy is lower in the morn­ings and evenings, which is why the power is reduced at these times, whereas during the after­noon the building is at its highest capacity, temper­a­tures tend to be at their hottest, the AHUs have to deliver a greater volume of air, and there is the most demand for cooling (Fig. 5). The ideal prereq­ui­site for this is the RadiPac’s RS485/MODBUS RTU inter­face, which enables the fans to be intel­li­gently controlled while also allowing the oper­ating data of each indi­vidual fan to be moni­tored. The RadiPac also enables differ­en­tial pres­sure measure­ment, as it has a pres­sure tap for connecting a differ­en­tial pres­sure trans­mitter. This also allows conclu­sions to be drawn about the air flow rate that is currently being handled. Thanks to the MODBUS inter­face, Qey’s soft­ware can monitor and control the speed as spec­i­fied by the schedule, and also monitor the air flow, energy consump­tion and, if neces­sary, alarms and quickly initiate coun­ter­mea­sures.

Figure 5 / Char­ac­ter­istic curve: Here, the modu­la­tion of the air flow over the day can be seen thanks to the time-depen­dent control system. After the retrofit, the new peak demand is only 16.5 kW (previ­ously 31 kW). (Fig. | ebm-papst)

Target achieved – energy consump­tion reduced by more than 60%

Docu­menting and moni­toring the oper­ating data are impor­tant for checking the energy savings achieved by the retrofit and can facil­i­tate addi­tional improve­ments to the control system in a further step. This is because after a certain time, during which the internal schedule is tested, further adjust­ments and refine­ment of the control system may be neces­sary. Constant moni­toring of each indi­vidual fan also ensures reli­a­bility: prob­lems can be iden­ti­fied quickly and nega­tive conse­quences prevented at an early stage.

Fig. 6: The control elec­tronics with RS485/MODBUS RTU inter­face are already inte­grated in the RadiPac. (Fig. | ebm-papst)

Finally, by moni­toring and docu­menting the oper­ating data, it is also possible to deter­mine how much the retrofit has saved: The peak demand for the old motor was 31 kW. After the retrofit, the peak demand for the maximum air flow required is 16.5 kW. The demand-based control system has also meant that the new maximum power consump­tion is only used occa­sion­ally and when required, and no longer non-stop (Fig. 6). The combi­na­tion of ebm-papst’s effi­cient RadiPac fans, Taka Solution’s exten­sive knowl­edge of building analysis, and Qey’s MatrixAir retrofit solu­tion resulted in a successful project imple­men­ta­tion. Energy consump­tion was reduced by more than 60%.