Heat recovery from LNG engines onboard modern cruise ships: dynamic modelling and system thermoeconomic optimization

Modern cruise ships are wide energivorous systems also for the included hotel services. From this point of view, very high energy demands (for HVAC systems, sanitary hot water production, artificial lights, auxiliary machineries, etc,) are required. Typically, the energy production is obtained by several diesel generators and, in the next future, also through innovative additional technologies (fuel cells, organic Rankin cycle power plants, etc.). In this paper the energy, economic and environmental impact performance analysis of such new polygeneration and multi-user systems is carried out. To this aim, a novel dynamic simulation model was developed and implemented in TRNSYS (version 17). Specifically, it regards an innovative cruise ship system layout in which the available heat recovered by engines generators fuelled by LNG is exploited to supply different Thermal energy Activated Technologies (TATs), such as: single-stage absorption chillers, multi-stage flash desalination units and organic Rankin cycle power plants. A suitable comparison is carried out with respect to a traditional system configuration in which the cooling energy, the desalination and the electricity production are obtained by electric vapour compression chillers, reverse osmosis desalination units and LNG engines generators, respectively. Aim of the carried out study is also the thermoeconomic system optimization for maximizing the heat recovery and the related profitability. Note that, all the components of the considered ship-plant system are detailly modelled in TRNSYS environment. In particular, the ship envelope geometry and the related energy features are modelled by means of the Google SketchUp TRNSYS3d plug-in and TRNBUILD (Type 56), respectively. A novel case study is also presented. It refers to a suitable cruise of the considered ship in the Mediterranean Sea. Note that, the ship space heating and cooling loads and demands, as well as the electricity and fresh water requirements, are dynamically assessed by considering the effective loads profiles and the different occurring ship orientation during the whole cruise. Here, a suitable hourly weather file (assessed on the base of the considered ship trip) was developed and different wind speeds (suitably calculated for ship motion and harbour hours) are taken into account. Different HVAC system layouts are modelled as a function of the selected indoor thermal zone. Here, innovative and conventional system components are investigated for comparison purposes. The results obtained through the carried out analysis showed that significant benefits in terms of reductions of fuel consumption, operating costs, and harmful emissions can be achieved. Useful design and operating criteria for ship manufacturers and users are also provided.