Cutting cabin costs

by | 16th June 2017 | News

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The Naval Architect: June 2017

Launched in June 2013, the EU’s JOULES project was a four-year study to explore possibilities for ultra-low emission shipping. The EU has set a target of a 40% reduction in greenhouse gas emissions by 2030 and an 80% drop by 2050 and critical to shipping’s contribution to these aims is the development of green technologies. In particular, the JOULES project – which brought together more than 40 industry partners including major players such as DNV GL, Rolls-Royce, Bureau Veritas and STX France – focused on simulation of vessel energy grids during the early design stage and the potential impact of existing and future technologies, both environmentally and economically.


In May 2017, The Naval Architect attended a conference in Hamburg which showcased the JOULES project’s final results, including presentations from 11 application cases and three ‘demonstrator’ cases. Among the most intriguing of these, certainly judging by the response it drew from delegates, was Meyer Werft’s research into developing a low-energy HVAC system for cabins onboard cruiseships.


Low energy cabin
The Meyer Group – which includes Meyer Werft, Meyer Turku and Neptun Werft shipyards as well as cabin manufacturers EMS PreCab and Piikio Works and the Marine Airconditioning Centre (MAC) Hamburg – typically builds three large cruiseships per year, comprising of around 10,000 cabins in total. Therefore, any energy saving which might be gained will be subject to a significant ‘multiplicator effect’ for these vessels.


Modern cabins are usually supplied with energy from the ship’s system, but the transportation of air through a vessel for a cabin’s air conditioning unit (ACU) sometimes requires more energy than the distribution of air itself.


Kurt Sommer, of Meyer Werft’s Research & Development division, explains: “In a conventional air conditioning system the hot air is lifted from cabins back to central unit, where some heat recovery is done and then blown off to a central blow-off point. The fresh air is taken from the central suction point, conditioned in the AHU [Air Handling Unit] and distributed to the many cabins on the ship… For that reason [high energy consumption] we already have to decentralise the secondary air systems so every cabin has a Fan Coil Unit (FCU).”


Meyer Werft’s Low Energy Cabin instead takes a more cellular approach to cabin air conditioning, going one step further by decentralising the fresh air system. Instead of drawing air from a central suction point it draws it from the balcony to the FCU, which in effect becomes a mini AHU, albeit with a centralised exhaust air system. The new air conditioning unit is slightly larger than a conventional FCU but still fits in the service corner cupboard of the cabin (see illustration) and is virtually silent, according to Meyer Werft.


“The concept of Meyer Werft’s air conditioning system depends on the reduction of pressure losses and therefore the reduction of electrical consumption from the transport of air. Weight is always a problem on a ship, especially in cabins, because they are quite high, so it’s an essential requirement to compensate additional weight which is caused by batteries, other electronics and air conditioning,” says Sommer.


In theory, each cabin would harvest its own solar energy using organic photovoltaic modules located on the windows, door and balcony (balustrade). This energy would then be stored within a battery system with an expected 10-year lifespan for supply during the night. Meyer Werft, which has been investigating the energy efficiency of cabins on both river cruisers and larger passenger ships, has also identified a large savings potential in the use of direct current (DC) distribution within the cabin grid, which allows for easier integration of alternative energy sources (i.e. like batteries, fuel cells and photovoltaics) without the conversion losses associated with AC. Measurements taken from the simulation model indicate that ACU-related electrical consumption per cabin would drop from 305W to 80W (a 74% saving).


Theoretically at least the German company is confident enough solar energy will be harvested during the day to supply the cabin for the next 24 hours, although Sommer admits that there would also be a back-up system given that the photovoltaics (which occupy a surface area of around 3.4m2) are unlikely to perform optimally on vessels operating in the north or in cloudier weather conditions.


Although the Low Energy Cabin ACU would be slightly heavier than current ACUs Meyer Werft is also exploring the use of lightweight composite materials for the walls, floor and ceiling of the cabin, which would more than compensate for the additional weight. Further energy savings have also been identified with the cabin lighting and television, again with a switch to DC grid. The units would require some additional maintenance time – one option considered during the early stages of research was for ‘clusters’ of cabins instead – but Sommer says this is “not excessive” and individual installations are far more straightforward overall.


A pilot Low Energy Cabin will shortly be installed onboard a drydocked cruise vessel in the US. Looking ahead, Sommer says Meyer Werft’s next step is to develop a DC exhaust system in addition to further refinements to the DC cabin grid, and to further explore the potential savings to be made from composite materials.

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