Hybrid Ferry Drives Even More Efficiently Thanks To Ventilation Retrofit

Zero emissions - that is the ambitious goal of the shipping company Scandlines. The company therefore continuously reduces emissions from the entire fleet. The best example of this is the Prinsesse Benedikte hybrid ferry, which runs on the route between Puttgarden in Germany and Rødby in Denmark. In addition to the usual diesel generators, there is also a battery block in the engine room of the ferry, with more to follow. It quickly became clear that it would not be economical in the long run to replace the performance of marine diesel engines bit by bit with energy from batteries. The ship also had to save electricity in order to keep the number and therefore the costs of the expensive electrical energy storage within reasonable limits. So Scandlines exchanged water pumps,switched the lighting to LED and sent the captains of the ships for training in energy-saving driving.

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Potentials identified in ventilation

In 2015 the shipping company then ventilated the ship. Until then, six large AC fans had brought fresh air from outside to the closed deck during the crossing, two of them carried the used air outside. Two fans stopped in the harbor while the other six vented the ship. Since the air had to be conveyed in the opposite direction in each of the two operating modes, some fans always ran backwards. This operating mode is particularly inefficient because fans are always designed for one direction of conveyance and consume drastically more energy in reverse operation. Carsten Johansen, the chief engineer at Scandlines, was also aware of this problem, which is why he asked the EBM Pope for a solution. "Since the consumption in this area was extremely high,we hoped to be able to save a lot of energy here,”explains Johansen.

So that the fans no longer have to run backwards, they are mounted on swiveling, square metal plates. They can be turned in the required direction of conveyance. As a result, the fans always deliver the air in the direction for which they are optimally designed. No modifications could be made to the ship for this. But despite the limited installation space, the principle works optimally.

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Control power precisely with EC technology

Another adjustment for more efficiency lies in the change in fan technology: Instead of AC fans, Hyblade EC axial fans now channel the air through the car deck. These can be steplessly regulated and thus adapted exactly to the power actually required, which varies depending on how many cars and trucks are on the deck. Furthermore, instead of individual large fans as before, fangrids with four smaller fans each are now used. This increases the area over which the air is conveyed, so that the air exchange on the car deck is further optimized.

The Hyblade fans combine the advantages of two materials: While the corrosion-resistant aluminum structure in the core of the wing ensures a permanent connection to the rotor, the jacket made of glass fiber reinforced plastic gives the wing an aerodynamically optimized shape. This light jacket affects the total weight of the fan and contributes to noise reduction thanks to its damping behavior.

Explosion-proof design

Since trucks with flammable substances also cross the Fehmarnbelt on the ferry, Scandlines placed another important requirement on the fans: they had to be explosion-proof. EBM-Pope was also able to meet this requirement because the company was the first manufacturer worldwide to develop EC fans in Atex design. Their impeller strength exceeds the standard requirements, a ground connection dissipates electrostatic charges and the power electronics are encapsulated in a pressure-resistant manner. The fans have been tested and certified in accordance with the European Atex 94/9 / EG (Atmosphère Explosive) product directive and thus meet all the requirements placed on devices in potentially explosive areas.

Additional information on how the car deck is ventilated

If the ferry is in the harbor, the gates to the quay are open so that sufficient air flows onto the car deck. For the air exchange, two fangrids are then turned outwards to further promote the draft.

During the crossing, the two Fangrids in the rear part of the ship convey the air inwards and the two Fangrids in the front part of the ferry back outwards. This prevents splashes of salt water from getting into the ventilation.

To save time in the ports, the ferries have two bridges so they don't have to turn. So the ship returns from the same position. Since the former front part of the ship is now the rear part and vice versa, the fans are turned in the other direction.

Huge savings

The entire package of product and solution convinced Scandlines, so the shipping company commissioned the conversion of a test unit. The comparative measurements for energy consumption after the retrofit exceeded the forecasts: If the single large AC fan had previously used 180 kWh, the four EC fans together now only need 30 kWh. Scandlines therefore converted the entire ventilation for the car deck during the next routine maintenance. "After this successful pilot project, we will also have the solution installed on the other three ferries that run between Puttgarden and Rødby," concludes Johansen. (sh)

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* Patrick Stern is market manager for refrigeration technology at ebm-papst Mulfingen GmbH & Co. KG.