Closed Loop Coolant Circuits in Chillers

A loop is the path that the coolant circulates in the cooling system. The coolant exits from the evaporator of the chiller, flows through the equipment or process that needs to be cooled, and then returns to the evaporator. The flow pattern of the coolant, the water quality, and the stability of the cooling system are all related to the type of loop. Common cooling loops include open loops and closed loops. This article explains everything about closed loop chillers.

Structure of a closed loop

A closed loop is mainly composed of a chiller, a sealed reservoir, a pump, and an expansion tank. The position and function of an open reservoir and a sealed reservoir within the entire circulation path differ. The open reservoir used in an open-loop system is located after the cooling target and before returning to the chiller.
 
It stores high-temperature coolant after absorbing heat, and handles makeup coolant and air-side heat exchange and heat exchange with air. The sealed reservoir in the closed loop is between the evaporator outlet and the process that needs to be cooled. It stores the cooled coolant for pressure stabilization and buffering.

Advantages of closed loop

• Prevent pollution
The circulation system of the closed loop is completely closed, and the coolant has no direct contact with the air. Therefore, it will not absorb dust, moisture and other impurities in the air and be polluted and deteriorated.
 
• Reduce coolant loss
Because the loop is sealed, the coolant will not evaporate or produce oil mist after absorbing heat. Compared with the open loop, the loss of coolant is reduced and it does not need to be replenished frequently. If you use expensive thermal oil, this can save you a lot of operating costs.
 
• Constant pressure operation
Most closed loops are equipped with an expansion tank to absorb the volume change of the coolant caused by temperature changes. The coolant absorbs and releases heat in the system, and its volume changes as the temperature changes. When the temperature rises, its volume increases.
 
However, the closed system cannot release the extra volume to the outside, which may cause the components to be damaged due to overpressure. The expansion tank contains compressible gas, and the coolant will enter the expansion tank after expansion, and the compressed gas will buffer the rising pressure. After the coolant has been cooled, its volume will shrink, and the expansion tank will release part of the coolant into the pipeline to prevent negative pressure or air inhalation in the pipeline.
 
• Compact
The closed circuit does not require an open reservoir, and the cooling system can be designed to be more compact, so that all components can be integrated in one space.

Limitations of closed circuits

In order to prevent air from entering, a large number of seals are used in closed circuits. If the joints, pipes, valves or water tanks are not sealed well, air will be mixed into the system. Therefore, it is necessary to check and replace the seals regularly. In addition, the closed circuit needs to manage the system expansion pressure, and an expansion tank, gas separation device and high-grade sealing materials are required, so the initial cost is higher.

Open loop circuits vs closed loop circuits

Conclusion

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