Technologies | Secondary convertors

The energy converters mentioned in the JOULES-Project are divided into primary converters (PC) that use fuels like oil or gas as primary energy and provide mechanical and / or electrical energy (e.g. Diesel engines) and so called secondary converters (SC) that use the energy provided by the primary converters like electric power and heat. The work packages cover electric motors, heaters and illumination.

An important item here is the use of so called “waste heat”. This energy is normally emitted to the environment as hot exhaust gas or cooling water. To save fuel, this energy may be recovered by waste heat recovery systems (WHRS) and transferred into useful energy at the ship. Various sorts of use of waste heat is covered such as the Diesel Combined Cycle, the Organic Rankin Cycle and the use of the Absorption Chiller.

Electrical converters

Electric Motors

For electrical motors, there is some potential to save energy by using high efficient motors. These motors are equipped with permanent magnets integrated in the rotating armature. That means that the electric field at the rotor is achieved by using strong permanent magnets that do not need any current. At standard motors, the field is generated by coils that need some electric power. Most of this current is gained back (reactive power). Nevertheless, reactive power has to be generated and wired.

Compared to standard motors, high efficient motors need less reactive power and the efficiency is approximately 2% higher. In addition to that the motor weight is only around 2/3 of a standard motor.

The price for high efficient motors decreased over the last years; therefore it is worthy to check whether the use of these engines is also an economical advantage.

Electric heaters

Electric heaters have only little potential to increase efficiency. Since the heat transfer is close to 100% the only potential lies in proper insulation.

Electric Power may be saved by replacing electric heat by thermal heat sources like steam, hot water or thermal oil. The most efficient way to get thermal heat is the use of waste heat supplied by piston engines or other prime movers.

Possible consumers at the engine room are electrical preheating units and trace heating for HFO-pipes. Preheating may be done by HT-cooling water, trace heating needs a higher temperature level and may be done by steam or other sources.


Electric illumination is another potential field to save energy. Energy efficient technologies like LED or vapour lamps allow power savings of about 90% compared to electric bulbs. Compared to fluorescent lamps, LED technology will save still some 50% of energy.

The total energy saving depends on the installed –and used- light capacity. Therefore the potential on passenger vessels is much higher compared to bulker or other merchant ships.

Conventional technology has to be used for strong spotlights, but these lights normally are shut off and are used only for a short time.

Waste heat recovery systems

DCC (Diesel Combined Cycle)

The Diesel combined cycle (DCC) is a combination of a Diesel engine and a Clausius-Rankine-water steam process. The steam process uses the heat of the Diesel engine´s exhaust gas to generate some electric power by a steam turbine driving a generator.

The steam process may be operated by saturated or overheated steam. Saturated steam may be used for small plants. The system is simple to install and operate but will provide quite a low efficiency. The electric output is estimated below 500 kWel. This range may be covered by cost-saving single-stage turbines.

For bigger plants, the steam should be overheated to operate multi-stage turbines and increase the thermodynamic efficiency. In this case a super heater is needed and the requirements on control system, steam quality and operation staff will increase. Due to higher possible efficiency, the additional costs should be covered by fuel savings in the long run.

ORC (Organic Rankine Cycle)

The Organic Rankine Cycle (ORC) may be seen as a steam cycle, with the water replaced by an organic media. The advantage of using organic fluids lies in the great variation of fluids that allow adapting the fluid to the available temperature levels. A steam process needs a heat source far above 100 °C to generate steam and a cooling source at around 40 °C or less. The ORC process may be operated on a wide range of 90 – 300 °C on the hot side and 10 – 120 °C on the cold side. Of course, the efficiency of the ORC-process will increase with the temperature difference between hot and cold side.

A second advantage of ORC is the use of any media as heat source like thermal oil, steam or hot water. A steam-cycle makes sense only in case the ship is equipped with a steam system for heating purposes. Despite the use on ships is possible, ORC-plants are operated mainly on land based plants. The technology is less widespread compared to steam systems.

Figure 1 - Adsorption chiller process

Adsorption chiller

Adsorption chillers offer the possibility to use waste heat to generate cool water. The process is divided into two steps that are changed continuously.

The physical effect behind the process is the capability of a material to collect water at its surface (Adsorption). By this Adsorption steam is condensed and an evaporation process is kept running at low temperature levels.

The diagram in Figure 1 shows the principal way the system works.

In the first step, water is sprayed over a heat exchanger and evaporated. The evaporation energy is taken from the chilled water side and cools down the water.

The generated steam is condensed at the surface of the adsorption material (green box at left side of graphic). To remove the condensation heat, cooling water is used to re-cool the material.

After some time, the adsorption material is saturated with water and the process has to be reversed. This is shown on the right side of the graphic. The water at the surface of the adsorption material is vaporized by hot water heating the material up. The steam is liquefied in the condenser on top of the graphic, re-cooled by cooling water.

With the changeover of hot and cold water and the opening and closing of the valves at the steam side, the process can be kept running continuously.

Figure 2 - Absorption cooling process

Absorption chiller

The absorption process is based on the different physical characteristics of mixed and separated fluids. A common mixture is generated by water and ammonia or a Lithium bromide solution. The basic function is shown on the following graphics from Figure 2.

The chilled water is produced by evaporation of a fluid like shown in the adsorption process. The steam is then absorbed by a solution of Lithium-bromide salt in water. The solution is then pumped to an evaporator, where the water is evaporated by heating up. The steam is condensed again in the condenser by cooling water. The condensate is used again, sprayed over the chilled water cooler bundles and evaporated.


Electrical converters

The described electrical converters provide some potential to save energy without bigger interference to the ship´s design. Here, the investment costs have to be checked towards the possible fuel savings. The savings will mainly depend on the operating hours per year; therefore there will be a strong relationship to continuous or part time operation of the ship.

Waste heat recovery systems

Steam and ORC-systems have to be engineered for each plant separately. Therefore a general statement to the economic viability will be hard to find.

In any case, the plants will affect the ship design since a lot of installation space and piping is needed. The more sophisticated the plants are built, the higher will be the requirements on crew skills.

Since the systems are more or less complex, they demand a continuous or at least long period operation. Here the operational profile of the ship will be very important.

Chiller-systems are easier to handle. They may be installed more like “black box”-systems and economical calculation will be much easier compared to waste heat recovery systems. Nevertheless, they will cause additional weight and high investment costs. Therefore a proper planning is still necessary.