Ways to Conserve Energy on Board - DNV

HT circuit
Figure 1. HT, LT and
cooling SW circuit with
SimulationX.
Finally, the seawater (SW) cooling system uses seawater <strong>to</strong>
cool down the water of the low-temperature circuit. Two
main seawater pumps run in parallel <strong>to</strong> provide a volume
flow of 2,300 m 3 /h <strong>to</strong> the central cooling unit.
LT circuit
Figure 1 shows a screenshot of the SimulationX model representing
the three cooling subsystems. The high-temperature
circuit for the main engine is displayed in the upper left. The
main engine model, located in the upper right corner, is not
modelled in every mechanical detail; rather, it is represented
by the three heat sources that charge the cooling water system,
comprising the lube oil, scavenge air and jacket cooling
systems. The heat exchangers (jagged components) shown
in the upper right area of the schematic belong <strong>to</strong> the lowtemperature
circuit, which is only represented in part on this
screenshot. The structure of the SimulationX model matches
the corresponding process flow very closely.
SW circuit
The low-temperature (LT) system likewise uses fresh water. It
cools down various components in parallel, such as the
lube oil, the main engine scavenge air, the auxiliary diesel
engines, alterna<strong>to</strong>rs, refrigerant condensers, excess steam
condenser, etc. In a further stage the low-temperature system
also cools down the high-temperature cooling system.
The water in this circuit flows at 1,840 m 3 /h and is cooled
from 50 °C <strong>to</strong> 36 °C. The low-temperature circuit is bypass-controlled
<strong>to</strong> maintain a constant temperature of 36 °C
downstream of the central cooling unit. Thus, depending
on the heat load from the engines and the seawater temperature,
parts of the cooling water bypass the cooler.
Variants and Simulation Results
Several variations of the actual cooling circuit were studied,
and the most promising two were analysed in greater detail.
Simulation studies of both variants were carried out <strong>to</strong>
investigate different operational scenarios. A number of operational
scenarios were defined based on various main
Table 1: Operational profile of a representative voyage
Operational mode Time (%) ME
workload
(% MCR)
No. of aux.
engines
used
Port 30 0 1
Manoeuvre 5 20 3
Restricted water /slow
steaming
35 45 2 – 3*
Sea passage 30 65 1 – 3*
* Varying number of auxiliary engines
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