A Central Cooling System (CCS) is a closed-loop freshwater cooling system used on ships to remove excess heat from the main engine, auxiliary engines, lubricating oil, compressors, and other engine room machinery. Instead of using seawater directly to cool each piece of equipment, the system circulates treated freshwater through the machinery, while seawater is only used to cool the freshwater in a central heat exchanger (central cooler). This design reduces corrosion, scaling, and maintenance while improving the efficiency and reliability of the machinery.
Marine engines and auxiliary machinery generate a significant amount of heat during operation. If this heat is not removed efficiently, machinery temperatures can rise rapidly, leading to:
The central cooling system maintains the operating temperature within the recommended limits, ensuring safe and efficient engine operation.
Ships generally use one of the following cooling methods:
In this system, seawater is pumped directly through heat exchangers to cool machinery.
Advantages:
Disadvantages:
In a central cooling system, freshwater circulates through the machinery in a closed loop, while seawater cools the freshwater through a central cooler.
Advantages:
The central cooling system operates using three interconnected circuits:
The seawater absorbs heat from the freshwater through the central cooler, while the freshwater removes heat from engines and auxiliary equipment before returning to the cooler.
The seawater circuit provides the final cooling medium for the entire system.
Main Components
Working
The LT circuit cools machinery that requires relatively lower operating temperatures.
Equipment Cooled by LT System
Typical LT water temperature ranges from 36°C to 40°C, depending on the vessel design and manufacturer.
The HT circuit cools equipment operating at higher temperatures.
Equipment Cooled by HT System
Typical HT outlet temperature is maintained between 80°C and 90°C using temperature control valves, depending on engine maker recommendations.
The expansion tank is installed at the highest point of the cooling system.
Functions
Freshwater makeup is generally supplied from the distilled water tank or freshwater filling system.
A three-way temperature control valve regulates the HT water temperature.
Functions
Proper temperature regulation improves fuel efficiency and reduces engine wear.
Modern ships commonly use plate heat exchangers as central coolers.
Advantages
The central cooling system offers several operational benefits:
Despite its advantages, the system also has some limitations:
The freshwater circulating in the system must be chemically treated to prevent:
Routine testing includes:
Problem | Possible Cause | Remedy |
High HT Temperature | Fouled central cooler | Clean heat exchanger |
Low Cooling Water Pressure | Pump wear or leakage | Inspect pump and seals |
Expansion Tank Overflow | Overfilling or thermal expansion | Check level and vent |
Low LT Temperature | Faulty temperature control valve | Inspect or replace valve |
High Differential Pressure | Blocked plate cooler | Clean plates |
Corrosion in System | Poor water treatment | Correct chemical dosing |
Always follow these precautions:
A central cooling system is a closed-loop freshwater cooling arrangement in which seawater cools the freshwater through a central heat exchanger, and the freshwater cools the ship’s machinery.
The HT (High Temperature) circuit cools the main engine jacket water and operates at higher temperatures, while the LT (Low Temperature) circuit cools auxiliary machinery such as lubricating oil coolers, charge air coolers, and compressors.
Freshwater minimizes corrosion, scaling, and marine growth inside engine cooling passages, improving equipment life and reducing maintenance.
The expansion tank compensates for thermal expansion, maintains water level, removes trapped air, and provides makeup water to the closed cooling circuit.
Plate heat exchangers provide excellent heat transfer efficiency, occupy less space, are easy to maintain, and often use titanium plates that resist seawater corrosion.
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