The document describes the central cooling system on a ship which previously used corrosive seawater but now uses a fresh water system. The fresh water system has high and low temperature circuits. The high temperature circuit pumps water from the engines to the fresh water generator and back to the pumps. The low temperature circuit then distributes this water to various auxiliaries. A temperature control valve regulates the mixture of waters to a suitable inlet temperature for the engines. The fresh water system requires less maintenance and investment than the previous seawater system but has higher initial costs and limitations during high sea temperatures.

1. Central Cooling SystemCentral Cooling System
Previously – mostly seawaterPreviously – mostly seawater
system.system.
All corrosive.All corrosive.
Prevention – rubber-lined pipes.Prevention – rubber-lined pipes.
Plenty of maintenance/repair.Plenty of maintenance/repair.

2. Sea Water CircuitSea Water Circuit
Sea water only pass through theSea water only pass through the
central coolerscentral coolers

3. HighTemperature CircuitHighTemperature Circuit
Fresh water pump pumps the water from theFresh water pump pumps the water from the
main engine and the auxiliary engine jacket.main engine and the auxiliary engine jacket.
Water is taken at the outlet (some are byWater is taken at the outlet (some are by
orifice) from the engines to the fresh waterorifice) from the engines to the fresh water
generator.generator.
From the outlet of the fresh water generator,From the outlet of the fresh water generator,
the water is led back to the pumps.the water is led back to the pumps.
The inlet temperature to the engine is aboutThe inlet temperature to the engine is about
65˚C and the outlet about 80˚C.65˚C and the outlet about 80˚C.
Whatever high temperature goes to the centralWhatever high temperature goes to the central
coolerscoolers

4. Low Temperature CircuitLow Temperature Circuit
Temperature of 35˚C.Temperature of 35˚C.
Distributed to two groups of auxiliariesDistributed to two groups of auxiliaries
connected in series.connected in series.
Within each group, the components areWithin each group, the components are
connected in parallel.connected in parallel.
1st group - air compressors, air-con plant,1st group - air compressors, air-con plant,
condenser for fresh water generator,condenser for fresh water generator,
2nd group - the air and lube oil coolers for the2nd group - the air and lube oil coolers for the
main engine. The air and lube oil coolers for themain engine. The air and lube oil coolers for the
auxiliary engines are also connected.auxiliary engines are also connected.
The bulk of the fresh water is then fed back toThe bulk of the fresh water is then fed back to
the central fresh water coolers.the central fresh water coolers.

5. Temperature ControlTemperature Control
The heat absorbed by the fresh water inThe heat absorbed by the fresh water in
the high temperature circuit will bethe high temperature circuit will be
transferred to the low temperature circuittransferred to the low temperature circuit
at the junction.at the junction.
The temperature regulated valve mixesThe temperature regulated valve mixes
water of about 45˚C from the lowwater of about 45˚C from the low
temperature circuit with warmer water oftemperature circuit with warmer water of
about 55˚C from the engines and freshabout 55˚C from the engines and fresh
water generator outlet to a suitable levelwater generator outlet to a suitable level
for the inlet to the engines.for the inlet to the engines.

6. Fresh Water Cooling SystemFresh Water Cooling System
– A clean system with reduced requirementsA clean system with reduced requirements
regarding cleaning and maintenance.regarding cleaning and maintenance.
– Less “wear” of pipes and valves, thereforeLess “wear” of pipes and valves, therefore
less maintenance cost.less maintenance cost.
– Less investment of cost as pipes need notLess investment of cost as pipes need not
be made for seawater usage.be made for seawater usage.
– Reduced number of valves made ofReduced number of valves made of
expensive materials.expensive materials.
– Constant to near constant temperature levelConstant to near constant temperature level
of cooling medium means easierof cooling medium means easier
temperature control of air and lube oiltemperature control of air and lube oil
coolers for main and auxiliary engines.coolers for main and auxiliary engines.

7. – No condensate on air side, reducing airNo condensate on air side, reducing air
fouling, owing to the higher andfouling, owing to the higher and
constant temperature for main engineconstant temperature for main engine
air coolers. Cleaner air coolersair coolers. Cleaner air coolers
compensate for higher cooling watercompensate for higher cooling water
temperature.temperature.
– No cold starting of main engine, sinceNo cold starting of main engine, since
the whole system is kept at warmthe whole system is kept at warm
temperature when the ship is in port.temperature when the ship is in port.

8. –Constant running condition for the mainConstant running condition for the main
engine as regards to cooling water,engine as regards to cooling water,
lube oil and air.lube oil and air.
–Less wear of cylinders liners, asLess wear of cylinders liners, as
consequences of running condition – noconsequences of running condition – no
cold corrosion/startup.cold corrosion/startup.
–Greater reliability of services offered byGreater reliability of services offered by
the central cooling system is importantthe central cooling system is important
for an unmanned engine room.for an unmanned engine room.

9. DisadvantagesDisadvantages
Initial high costInitial high cost
Limitation of lower temperature,Limitation of lower temperature,
especially for main engine air cooler,especially for main engine air cooler,
also during high sea water temperaturealso during high sea water temperature