How maritime waste energy recovery works

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How maritime waste energy recovery works
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How maritime waste energy recovery works

– by Paul Spoorenberg, 15/01/2021

Did you know that marine diesel engines have an efficiency of just 50%? The remaining energy released from fuel combustion is lost to the atmosphere in the form of heat. This blog explores how recovering thermal energy will radically improve your vessel’s sustainability.

In this guide we handle the following topics:

  • What is waste energy?
  • Methods of waste energy recovery
  • How to utilise waste energy

What is waste energy?

It would be great to have an engine, generator or even a process in which all the energy we put in is converted to work but, alas, that’s not how physics works. In fact, it is impossible to convert all the input energy into work due to a property called entropy.

How and why nature operates in this way you can read in this blog. But in short it comes down to the fact that there always needs to be some waste heat.

During the combustion of fuel, chemical energy is converted into mechanical and thermal energy. The first sets the engines pistons in motion, the second leaves the vessel with the exhaust fumes as waste heat.

However, waste heat doesn’t mean that the energy needs to be wasted.

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Image 1: Transfer of energy in fuel

Methods of energy recovery

There are basically two ways in which thermal energy from the diesel engine’s waste heat can be recovered:

  1. The engine cooling system
  2. The engine exhaust gases

1) Engine cooling system

Marine diesel engines need to be cooled to avoid failures. High engine temperatures lead to all kind of problems such as thermal expansion that causes seizure or excessive thermal and mechanical stress which damages the pump seals.

While smaller engines are cooled by air, most marine diesels are water or oil cooled. These primary coolants circulate continuously in a closed cooling system with a secondary system taking the heat from the primary to avoid overheating. Secondary coolants may be sea water or air, but it can also be a freshwater system that uses the heat for other purposes.

2) Engine exhaust gases

Exhaust gas temperatures range from around 300°C to 500°C, depending on the engine design and load. That’s an enormous amount of energy which can be used in a variety of ways. The most commonly used method to recover waste energy is via a specially designed heat exchanger.

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Image 2: Recovering waste heat

How to utilise waste energy

There are many ways to utilise recovered thermal energy, including steam turbine generators, economisers, turbo chargers and freshwater generators. In this blog we would like to highlight the systems that are HVAC related.

1) Hot freshwater

Hot water used for sanitary purposes such as showers and many other purposes. The water is heated up and stored in boilers. Thermal energy from waste heat is a good source for firing up these boilers too.

2) Heating system

The heaters inside air handing units or blowers to warm up technical spaces use electric or water-fed coils. The latter are ideal for utilising thermal energy from waste heat.

3) Absorption chiller

As well as heating things up, waste energy can also be used to cool things down. An absorption chiller is a good example. These chillers require a heat source to fuel their physical processes and are especially designed to use waste heat as a power source.


There is an enormous potential in waste energy which can be used in many kinds of ways. Other means of energy need to remain accessible, of course, as this power source is only available when vessels have their engines running. Nonetheless, ships are primarily intended to travel from a to b so waste energy is available most of the time.

Like to find out the best way to use waste energy on your vessel? Contact one of our engineers. For all other things HVAC, stay tuned to

Paul Spoorenberg | Sales Manager

Paul Spoorenberg has been working at H&H since 1994. During his career he gained valuable expertise in HVAC solutions for all kind of vessels in the Commercial, Offshore, Naval & Yacht segments.