For his master’s thesis in Mechanical Engineering at Aalto University, Julius Kuula set out to solve a challenge that every cruise ship faces: what to do with surplus waste heat generated during sailing. Supported by Foreship as his collaborative partner, intern Julius investigated how thermal energy storage (TES) using phase change materials (PCM) could turn otherwise lost energy into a resource for cutting fuel consumption and emissions.
Cruise vessels generate large quantities of waste heat while underway. While a lot of the waste heat can be utilized for different heating purposes and fresh water generation, some of the waste heat is discharged into the sea or air. Yet, when the ship is alongside the berth, onboard demand for heating remains. Shore power can reduce emissions, but converting the shoreside electricity to heat onboard is expensive.
Kuula’s study modelled how TES could bridge the imbalance by capturing waste heat while at sea during sailing and re-using it later in port.
Using data from a reference cruise vessel and a detailed numerical simulation of the waste-heat recovery circuit, Julius demonstrated that a compact PCM-based TES unit could meet the vessel’s high-temperature water circuit demand for a nine-hour port stay without using auxiliary boilers. However, only a portion of the total heating demand can be met using TES, as it is not suitable for steam storage. Therefore, TES can be effectively applied to HT (high-temperature) cooling water consumers, such as potable water heating and air-conditioning (AC) reheating and/or preheating.
“The system would store enough energy while sailing to supply all the HT circuit heat needed at berth,” he explains. “By doing so, it could reduce fuel consumption and CO₂ emissions during each port call.”
The findings are significant. A 108-cubic-metre tank could save 10.8 MWh of energy per port stay and cut CO₂ emissions by around 3 percent. Over a year of operations, the savings could exceed 2,000 MWh, depending on the operational profile of the vessel. The study also found that the technology would integrate readily with existing waste-heat systems on board, provided design choices are optimized from the start of a newbuilding project.
In this case as well: the use of boilers cannot be avoided as steam is still required. However, the implementation of TES eliminates the need for an oil-fired boiler (OFB) to produce heat for consumers in the high-temperature/waste heat recovery (HT/WHR) circuit, namely potable water (PW) and air-conditioning (AC) heating.
The study offered Julius the chance to apply academic theory to a practical and timely issue. “Energy efficiency and emission reduction are central to the future of ship design,” he says. “Working with Foreship gave me insight into how these technologies could be implemented in real ships and how detailed design decisions influence performance.”
Foreship’s Head of New Technologies, Joonatan Haukilehto, says that Kuula’s project exemplifies the purpose of Foreship’s internship and thesis programs. “We aim to give young engineers the opportunity to contribute meaningfully to the evolution of sustainable ship design,” he comments. “Julius’s work shows how the next generation of naval architects and marine engineers are already helping to redefine what efficient, climate-aware passenger shipping can look like.”
Since completing his studies, Julius has been hired by Foreship as a Project Engineer. A bright and stimulating career lies ahead.
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