Decarbonization of Maritime Transport
How to reduce energy consumption in maritime buildings while lowering their carbon footprint, explained by Hervé Chesnel.
Have you ever noticed that there’s sometimes a breeze from the air conditioning when you’re on board a ship? Hervé Chesnel, Technical Director of Innovation at the Saint-Nazaire shipyards for Axima Marine (a division of Equans), explains! He works with both the cruise ship industry and the military to design HVAC (heating, ventilation, and air conditioning) systems on board ships, which presents several challenges compared to land-based buildings.
How do environmental constraints differ between the construction of land-based buildings and that of cruise ships?
Although it is the same profession, the fundamentals are similar, but the environmental constraints differ radically. The first constraint is the climate. When constructing a land-based building, it is designed for a local climate—say, a maximum of 32°C and a minimum of -5°C. In contrast, a cruise ship is designed for a tropical climate—hot and humid—but also for extreme conditions like those in the Arctic, at -20°C. These conditions therefore require a wide range of design criteria.
In addition to climatic constraints, what other specific factors must be taken into account when designing a ship’s HVAC system?
Beyond weather conditions, ships are subject to international regulations, such as the SOLAS (Safety of Life at Sea) Convention, which defines fire safety standards for ships. This international regulatory framework clearly distinguishes marine facilities from land-based facilities. Today, the shipping industry is decarbonizing, which poses a number of energy challenges.
Speaking of which, how is the maritime sector approaching decarbonization?
To date, shipping accounts for about 3% of greenhouse gas emissions—equivalent to data centers, air travel, or Japan’s carbon footprint. The maritime sector, a major player in global trade, is taking action to address this issue. This proportion could rise to 17% by 2050 due to the growth of global trade, since 90% of goods are transported by sea. On a ship, the main source of carbon emissions is propulsion. Shipowners have been exploring possible solutions for years to decarbonize this energy-intensive process. From a technical standpoint, wind power can be harnessed by deploying sails, or a bubble system can be installed beneath the hull to reduce a ship’s drag. Speed can also be reduced and routing optimized to lower a ship’s carbon footprint. Propulsion is not the only area where decarbonization efforts can be focused. Air conditioning, ventilation, and heating—also known as “HVAC”—are also major sources of energy consumption.
What solutions have you developed to reduce the carbon footprint of HVAC systems?
Our first step was to try to understand where the energy used for HVAC came from. To do this, we developed various tools.
The first, a tool called “CoTools,” allowed us to calculate the carbon footprint of our systems as applied to the maritime sector, with a more commercial focus on defining this footprint and exploring technical options.
As part of this effort, we created a second tool designed to define a ship’s energy consumption profile in order to understand the operating environment and assess the percentage of energy consumed, with a focus on our HVAC system.
These two tools allowed us to determine that the major challenge with HVAC is energy consumption. The second tool revealed that, for a passenger ship, our system is the second-largest source of energy consumption, accounting for nearly 85% of energy use while in port.
Energy consumption therefore varies depending on whether the ship is docked or at sea, but how exactly?
A cruise ship consumes energy at sea, but also when it is docked. During port calls, passengers go ashore to visit the port, but the ship continues to operate for those who remain on board and the crew.
On a ship carrying 7,000 passengers, there are about 3,000 crew members, so the kitchens, laundry facilities, and hospitality services remain operational to prepare evening meals. The ship is like a small town and continues to operate while docked, so the need for air conditioning remains constant; only the propulsion system shuts down.
When the ship sets sail again, its overall energy consumption increases six- or sevenfold due to propulsion.
What are the current challenges in reducing the energy consumption of the HVAC system on board?
We are, in part, following the lead of the terrestrial sector, where there is a greater focus on energy consumption and different regulations are in place.
Today, building on these advances, we are working on products and equipment that deliver better energy efficiency. We are also integrating automated systems that minimize energy waste in our systems and are reevaluating our practices. One constraint in the maritime sector is compactness; one of the design goals of HVAC is to create compact installations. To achieve this goal, there is a tendency to use high-speed systems, which consume a lot of energy to transport water, air, or heat transfer fluids.
One approach is to reduce speeds to lower energy consumption, but this would take up more space on ships. Consequently, the design is being reevaluated to reduce energy consumption and develop high-performance, low-pollution, and compact equipment.
You’re clearly passionate about your work. What attracts you to this field?
I love technology—it’s what has shaped me professionally. I love understanding how things work and ensuring that the operational model I have in mind aligns with what I design.
What drew me to the Navy was the responsibility for our designs. There are very few intermediaries between us and the shipyard, unlike in land-based organizations. We design and are responsible for our designs, which is important to me. This also involves taking ownership and projecting ourselves onto the object we’re designing. For example, on the first helicopter carriers built in Saint-Nazaire, in the event of a bacteriological or chemical threat, the ship pressurizes to prevent toxic gases from entering. This was a new concept at the time, and we had to anticipate how it would be used.
Does the military sector also share this commitment to reducing its energy consumption?
Although the number one requirement for a military vessel remains its operability—that is, its ability to function regardless of conditions—energy consumption is increasingly being factored into specifications. This criterion, discussed with clients, leads to an assessment of whether energy-efficient solutions are technically feasible. It is a strength to be able to propose innovative ideas with long-term potential.
You seem to be a passionate teacher. Is it important to you to share your knowledge?
Explaining things is difficult; you have to use simple language to describe physics concepts, and sometimes come up with original visual representations of certain phenomena. In my free time, I draw and paint in a travel journal, often incorporating text and images inspired by my dreams, fears, and thoughts.
