What is an Open Loop Circuit in Chiller

The loop in a chiller system refers to the complete circulation path of the coolant, from the outlet of the evaporator through the equipment and back to the evaporator inlet. This path includes the evaporator of the chiller, the equipment to be cooled, the process and the pipeline. Open-loop and closed-loop configurations are two common types of cooling circuits. This article explains what an open loop is.

What is an open loop circuit?

An open cooling loop means that the coolant will have direct contact with the outside world at some point during the circulation process. The water tank or reservoir in the loop is open to the atmosphere, allowing direct contact between the coolant and ambient air.

Structure of an open loop circuit

A typical open loop consists of a chiller, an open reservoir, a water pump, and the target equipment or process to be cooled. The evaporator of the chiller system evaporates the refrigerant and absorbs heat to cool the coolant. As an open system, the reservoir stores heated coolant and is in direct contact with the air. The function of the circulating water pump is to transport the coolant from the reservoir to the equipment or process that needs to be cooled.

How does an open loop circuit cooling system work?

After the refrigerant in the industrial chiller evaporates at the evaporator, it absorbs the heat of the coolant and the temperature of the coolant drops to the set value. Driven by the circulation pump, the low-temperature coolant is transported to the equipment or process along the pipeline. After picking up heat from the process or equipment, the coolant will flow back to the open water tank and be sent to the evaporator again for the next cycle under the push of the water pump.

Advantages of open loop circuit

• Water level visualization
The open water tank makes it easy to see the water level of the coolant directly, without the need for additional water level sensors. When the water level is low, it can be added at any time without stopping the machine to vent or dismantle the pipeline.
 
• Easy to maintain
The open circuit uses a water tank plus water pump structure with a simple structure. There is no need to repeatedly vent during installation, and debugging is convenient. It has a short circulation path and is not easily blocked by impurities. Even if there are impurities in the water tank, it is easy to disassemble and clean.
 
• Branch liquid supply
The open circuit can supply liquid at constant pressure for multiple processes and equipment without the need for balancing valves and pressure control logic.
 
• Thermal buffer
The water tank used in the open circuit can store high-temperature coolant. When the instantaneous heat load of the process increases, the coolant stored in the water tank can act as a thermal buffer, avoid drastic temperature fluctuations, and reduce the instantaneous pressure of the chiller refrigeration system.
 
• Low initial cost
Open-loop chillers do not use closed expansion tanks, pressure controllers, and complex pipeline seals, and have a low initial cost.

Limitations of open loop circuit

In an open water tank, the coolant will come into direct contact with the air and directly absorb impurities such as moisture, dust, and oil mist in the air. In particular, Glycol is highly hygroscopic, and after absorbing water, it will change physical properties such as concentration, viscosity, and freezing point, causing performance degradation.
 
If there are too many impurities in the coolant, they will accumulate in the pipeline, causing pipeline blockage. Moreover, high-temperature coolant is easy to evaporate and needs to be replenished regularly. If toxic, corrosive, or volatile liquids such as heat transfer oils are used as coolants, they will evaporate and leak in the open system, posing a safety hazard.

Maintenance of open loop circuits

The coolant in the open circuit is easy to evaporate at high temperatures and should be replenished regularly to prevent the pump from running dry or drawing in air due to low liquid level, which may cause pump cavitation damage. The water tank should be inspected and cleaned at least once every 3 months to prevent impurities from clogging the pipes. In addition, in order to ensure heat exchange efficiency, the coolant needs to be replaced regularly to prevent deterioration and corrosion of the cooling system.

Conclusion

Open circuits are generally used in working conditions where accuracy and cleanliness are not strictly required. If you want to control the temperature of precision equipment and processes such as semiconductors, MRI and CNC machine tools, closed circuit chillers are the best choice. LNEYA provides standard closed-loop circuit chillers and customized services. LNEYA offers a full range of temperature control solutions tailored to your application needs.