The water around the ferry Prinsesse Benedikte shimmers metallic blue as she leaves the harbor in Puttgarden on the German island of Fehmarn and heads for the Danish port of Rødby. What very few passengers know: They’re on a hybrid ferry that gets its energy from both diesel generators and batteries. One who knows that very well is Carsten Johansen, who is standing on the ship’s bridge and taking a close look at the instruments instead of enjoying the sun over the Fehmarn Belt.
Scandlines facts and figures
The German-Danish ferry operator Scandlines operates two short ferry routes with high capacity and frequency and with a green vision for the future. On the Puttgarden-Rødby route alone, the five ferries transport 1.5 million cars, 400,000 trucks and 12,000 railroad cars annually. The ships are in constant use, spending an average of only 15 minutes in port and reaching an official total of 104 departures per day.
Johansen, who is affectionately called the “energy minister” by his coworkers, is chief engineer at Scandlines, where he is steering the helm more and more toward efficiency. “Sustainability isn’t just part of my job, nowadays it also dictates my personal lifestyle. That’s inevitable when you concentrate on this subject so much.” At home, the 57-year-old therefore replaced an old oil fired heating system with an energy efficient heat pump, installed solar panels on the roof and changed lighting to low energy LED lamps.
Since 2003, Johansen’s daily work has involved bringing the ferries between Puttgarden and Rødby ever closer to the goal of zero emissions. Back then he replaced the first of five diesel generators with an electric energy storage system. It quickly became clear to him that it would not be enough to replace the power from the ship’s diesel generators bit by bit with battery power. The ship also needed to save electricity in order to limit the number and cost of the expensive batteries. So Scandlines replaced water pumps, converted to LED lighting, and had its captains trained in energy-saving sailing techniques. In 2015, the energy minister took on the ship’s climate control system. “It used an enormous amount of power, so we hoped we could save a lot of energy there.”
Fresh air for the car deck
That’s how Niels Knokgård and Torben Kirkholt came to take a short voyage to Germany and back again. Johansen had invited the technical sales representative from ebm-papst Denmark and his managing director to an on-site visit. During the short trip, in addition to examining the ventilation system in the passenger area, the two also took a close look at the system in the 12,000 cubic meter car deck, where eight large AC fans were responsible for air circulation. During the ferry ride, six fans brought fresh air into the closed deck from the outside while two others conveyed used air to the outside.
In port, two fans took a break while the other six aired out the ship. Since the two modes required the air to be transported in opposing directions, some fans had to run in reverse. “That’s a very inefficient way to operate a fan,” Knokgård pointed out to the energy minister as the three men stood in front of the AC giant. “Yes, that’s precisely the problem,” sighed the latter. “If only we could turn the fans around.” A sentence Knokgård and Kirkholt couldn’t forget.
Not afraid to sully their hands: Carsten Johansen, Chief Engineer at Scandlines (in the middle) and Torben Kirkholt and Niels Knokgård from ebm-papst. (Photo: Henrik Petit)
Carsten Johansen on the car deck of the hybrid ferry. (Photo: Henrik Petit)
The ventilation system of the car deck can now be controlled centrally and precisely. (Photo: Henrik Petit)
On the Puttgarden-Rødby route, five ferries transport 1.5 million cars, 400,000 trucks and 12,000 railroad cars annually. (Photo: Henrik Petit)
“It was obvious that we can’t easily turn a fan around,” says Knokgård. After puzzling over the problem a bit, he and his colleagues came up with the idea that they didn’t have to turn the individual fans at all. Together they developed a pivoting square metal plate on which four fans are mounted so that they can operate in both directions without running in reverse. “Since no modifications to the ship are allowed, there wasn’t much room for us to work with. That means the fans can’t be pivoted by exactly 180 degrees,” explains Knokgård, but the idea works anyway.
How the car deck is ventilated
When the ferry is in port (A), the doors facing the quay are open so that sufficient air flows into the car deck. Two FanGrids are turned outward to provide extra air circulation support.
During a crossing (B), the two FanGrids in the ship’s stern take air in and the two FanGrids at the bow expel it to keep saltwater spray out of the intake air.
To save time in port, the ferries have two bridges so they do not need to turn around; a ship can embark on its return voyage from the same position. Since the former bow of the ship is now its stern and vice versa, the fans at each end are turned in the opposite working direction (C).
But with this new concept, ideas for increased efficiency were far from exhausted. Replacement of the AC fans with fans using EC technology seemed an obvious next step. The latter can be smoothly adjusted to the output that is actually required, so they can be operated very economically. To generate even more pressure in the same amount of space, Knokgård suggested using FanGrids with four smaller fans instead of large single fans, increasing the area over which the air is conveyed and further improving the air exchange on the car deck. When Johansen heard about the idea at the next meeting, he was enthusiastic and commissioned a technician to install a test unit with a pivoting metal plate and four EC HyBlade fans.
Explosion protection included
A glance at the car deck shows that not only globe-trotting tourists and seasoned commuters use the connection between Denmark and Germany, but also a lot of truck drivers. Some of the trucks transport flammable substances, and that places another important demand on the fans. “Of course it was a big plus for us that ebm-papst is the only manufacturer that offers EC fans in an explosion-proof ATEX design,” says Johansen. After refitting the test unit, the chief engineer made some comparative measurements and found that the savings actually exceeded the expected values.
The payback period for the change from AC to EC technology is just one year.
Carsten Johansen, Chief Engineer at Scandlines
A finding with consequences: During the next routine maintenance, Johansen had another three FanGrids installed in the ferries while they were in the docks. And Scandlines also switched to EC fans for the ventilation system in the passenger area. The results are very impressive. Thanks to the ventilation changes, Scandlines now achieves total energy savings of two million kilowatt-hours per year and ship; the payback period for the project is a little over one year. “That’s a giant leap for us,” says Johansen. Following up on the successful pilot project, Scandlines will implement the solution on the other three ferries that ply the route between Puttgarden and Rødby as well.
Meanwhile, the Prinsesse Benedikte has docked in Rødby. Johansen is stretching his legs on the pier as an unending stream of cars and trucks flows out of the ship. “Our goal is to achieve emission-free and fully electric-powered travel within the next few years,” he says. “If all goes well, we might already get there by 2019.” The energy minister already has an idea for the next step. After all, the ferry has another car deck…