See the ship as a whole and save energy

When Fredrik Ahlgren, PhD student at Linnaeus University and Francesco Baldi, PhD student at Chalmers met and realized that they were working on similar things they decided to join forces. Now they have written an article together. 

M/S Birka Stockholm. Photo: Birka Cruises AB

Both Fredrik Ahlgren at the Kalmar Maritime Academy at the Linnaeus University and Francesco Baldi at the Department of Shipping and Marine Technology at the Chalmers University of Technology are interested in the efficiency of the ship as a whole and how to optimize it. They see the ship as one big energy system instead of focusing on the details. 

This is a proven concept when looking at energy in power stations, but a relatively new thing in maritime research. Baldi has earlier developed a model for analyzing the energy loss in one of Laurin Maritime’s bunker ships. His research contributed to the improvement of the energy efficiency of the company’s fleet.
Ahlgren has been gathering data at the MS Birka Stockholm, a passenger ship that resides in Stockholm. They met at Francesco’s licentiate seminar in Gothenburg and they found their similarities.
The data that Ahlgren had, together with Baldi’s model, started the collaboration between the two.

Francesco Baldi

- It is very rewarding to use the model on a passenger ship, Baldi says. The research becomes much more interesting since the energy system is much more complex.

The step from mapping up the energy system in a tanker boat to doing the same with a passenger ship is quite large. In the passenger ship they have to take many more parameters to account such as restaurants, pools, saunas and much more. 

They look at all the parts of the vessel that are using energy. The main engines, electric usage, thrusters, bow thrusters, boilers etcetera. The data is taken during one full year to see how much energy the ship uses. Since they already know how much fuel they put into the ship, now they check how much of the fuel the different parts of the ship use.
In the diagrams they use it is easy to see how much of the energy put in that goes to the different parts of the vessel. Much goes to propulsion and electricity, but a great deal goes to heat.
One aspect of the study that the researchers are particularly fond of is the concept of exergy.- Imagine having a large tank of water at 100 degree Celsius and a smaller tank with water at 1000 degree Celsius, both of different volumes but the same amount of energy. If you measure the energy you will get the same figure in Joule in both tanks. But still you can’t do much with the water in the large tank, whilst the water in the smaller tank can run an engine.  The exergy concept considers how much mechanical work you get from the energy, says Ahlgren.

One big difference between energy and exergy is that exergy may be destructed. If you let the small tank in the example above cool off the potential mechanical work is gone.
                                                                                         Exergy flow of M/S Birka shown in a Sankey diagram.
When using the exergy concept in the analyzing scheme you get a much more usable picture of where a ship is effective and where it is not and where most of the exergy is destroyed.
- So if we want to optimize something it is a smart thing to look at where most the exergy is destroyed, Fredrik says.
This research wouldn’t be possible without a ship to get the data from and both researchers are grateful that Laurin Maritime let Baldi onto their ship and the Eckerö Group, that owns MS Birka Stockholm, let Ahlgren onto their ship. Both of Ahlgren and Baldi have met reluctance from companies when they have tried to get access to ships. But at Eckerö they thought differently.- We were a little sceptical when Fredrik came to us and asked for access, but we did a reconsideration about letting on researchers aboard our ships. We are curious about what he can contribute with, say Andreas Strömberg, Technical Superintendent at the Eckerö Group.
                                                                                                                                                                                                                                                                     Fredrik Ahlgren
Fredrik Ahlgren has already published an article about using ORC engines on-board, and now he and Francesco are about to publish an energy and exergy analysis based on their joint work.
Francesco Baldi and Fredrik Ahlgren will present a poster together at the Swedish Maritime Day April 20.