© Bernd Schifferdecker; Gernot Walter

All systems go offshore

Not much time and lots to do: Walter Roller GmbH was under a lot of pres­sure to deliver the air condi­tioners for the offshore converter plat­form BorWin gamma.


The bags are packed. Rainer Ehrhardt and his colleagues are just waiting for the call to travel to Dubai to commis­sion their air condi­tioners. But the call does not come. “The quality we deliv­ered was just too high,” explains Ehrhardt, strug­gling to refrain from laughing. “Our systems worked from the word go.” Ehrhardt is a sales engi­neer at ­Walter Roller GmbH. From Bremen, he supports the maritime contracts of the company based in Gerlingen near Stuttgart.

A hive of activity on site

The story with Dubai was a very special task. At the Dry Dock World there, the BorWin gamma converter plat­form from network oper­ator TenneT was towering up into the blue Arabian sky. Its desti­na­tion: the Hohe See and Global Tech I wind farms, around 100 kilo­me­ters off the coast of the North Sea island of ­Borkum. In the fall of 2018, following comple­tion, the 18,000 metric ton yellow ­colossus made the 12,000 kilo­meter journey on board a trans­port ship.

The Walter Roller team waiting: Rainer Ehrhardt, Wolf­gang Krenn and Ingo Raisch. (Illus­tra­tion | Bernd Schif­fer­decker; Gernot Walter)

164 Roller air condi­tioners operate in the offshore plat­form. They are mounted in communal areas, such as the canteen or control room, as well as in tech­nical func­tional areas, such as the converter rooms. The order kept the manu­fac­turing company, with its 110 employees and head-quar­ters in Gerlingen, Germany, quite busy. “All of the units for the project were one-off prod­ucts,” says Managing Director Wolf­gang Krenn. “Producing this number in a rela­tively short space of time — it was a hive of activity here.” But it was not just the short time period between the order and delivery to the Port of Hamburg that was chal­lenging — the tech­nical, spatial, and admin­is­tra­tive require­ments were also special.

Copper, not aluminum

As the salt content of the sea air is extremely high, the stan­dard aluminum ribs in air condi­tioners corrode faster. For BorWin gamma, Roller there­fore used ribs made from copper for the heat exchangers. This made the units about a third heavier, however. “This makes no differ­ence for smaller units,” explains Head of Devel­op­ment Ingo Raisch. “But for large air coolers, we had to attach rein­forced mount­ings.”

„If some­thing isn’t working in the chiller room of your local baker, you just drop by. That is, of course, diffi­cult with this project.“
Rainer Ehrhardt, sales engi­neer at Walter Roller

And from a weight of 25 kilo­grams, special mount­ings were neces­sary, so-called lifting lugs. “We attached each indi­vidual unit to a crane in order to test whether they work — since then everyone here in produc­tion knows what lifting lugs are.” But the inside of the unit also has to cope with salt so that both cold water and salt water can be used for cooling.

Ribs made of aluminum are stan­dard in air condi­tioners. However, the mate­rial corrodes faster in air containing salt. For BorWin gamma, ribs made from copper were used in the heat exchangers. (Illus­tra­tion | Bernd Schif­fer­decker; Gernot Walter)

The air coolers must also be able to heat the air. This is because there is a risk of conden­sa­tion forming in the rooms on board the plat­form on days when the turbines of the wind power plants are stationary. As there is plenty of elec­tricity, the choice was made for elec­tric heating. “For us, this was a real excep­tion which was also quite diffi­cult to realize,” says Raisch, looking back. Further­more, it had to be ensured that the surface of the units did not exceed a certain temper­a­ture. “During our tests, it some­times took hours before the heating element had brought the unit up to the crit­ical temper­a­ture — and we had iden­ti­fied the hottest point on the unit.”

The units were also finally signed off in Gerlingen. For one week, a large inter­na­tional team assessed the perfor­mance and sound measure­ments on the indi­vidual unit types. “This only worked out because a small area in produc­tion was in the process of being converted at the time and so was empty,” explains Managing Director Krenn. The focus of the tests was on dura­bility, as Rainer Ehrhardt high­lights: “If some­thing isn’t working in the chiller room of your local baker, you just drop by. That is, of course, diffi­cult with this project.”

This also demanded the highest level of reli­a­bility from the fans in the units. This is provided by the ebm-papst centrifugal fans in the ten large air condi­tioners, and the axial fans in the high-perfor­mance air coolers. In their motors, partic­u­larly robust bear­ings are used, for example.

Trav­el­ling colossus: the converter plat­form Borwin gamma at the start of its journey at Dubai. (Illus­tra­tion | Bernd Schif­fer­decker; Gernot Walter)

Thanks to the EC tech­nology of the fans, there was one require­ment that the team did not have to worry about: “Thermal contacts were required for connecting the fans — but here the elec­tronics are already inte­grated.”

Along­side the high quality when it came to tech­nology and produc­tion, a third factor played a crucial role in the project going so well: the detailed docu­men­ta­tion. “We had already solved lots of even­tu­al­i­ties in advance,” explains Krenn. “This is why we have not had any queries so far.” But also no trip away.

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