What Are Refrigerant And Coolant In Refrigeration System?

Many people have trouble distinguishing between refrigerants and coolants. This blog post explains the definitions of both, highlights the key differences between them, and explores their respective roles in a chiller’s refrigeration system.

What Is Refrigerant?

We know that in nature, heat always flows from warmer areas to cooler ones. What makes a refrigerant unique—and earns it the name—is its ability to reverse this natural flow. A refrigerant is capable of taking in heat from colder air and discharging it into warmer air. In effect, it extracts “cooling” from warm air by redirecting the flow of heat. This ability to create a cooling effect even in a hot environment is what defines a refrigerant.

What Is Coolant?

A coolant plays only a supporting role in refrigeration systems. Its primary function is to carry and transport heat from a higher-temperature area to a lower-temperature one. It simply serves as a medium for the natural flow of heat.

For instance, in the refrigeration cycle system of a chiller, heat from the object being cooled is first transferred to the coolant. The coolant then carries that heat to the refrigerant, which is at a lower temperature. Throughout this process, the direction of heat transfer always follows nature’s rule—moving from high temperature to low temperature.

Refrigerant VS Coolant: Understanding The Difference

Refrigerants, also known as cooling media, play a key role in chiller refrigeration systems by absorbing, transferring, and releasing heat. During operation, the refrigerant undergoes phase changes as it switches between liquid and gas states.

In general, refrigerants are expected to have excellent thermodynamic properties. Specifically, the critical temperature should be higher than the condensation temperature, and the saturated pressure at the condensation point should not be excessively high. Optimal refrigerants also feature a low normal boiling point, low specific heat capacity, low adiabatic index, high heat transfer per unit volume, high thermal conductivity, low viscosity, low density, and robust chemical stability.

However, a coolant functions like a delivery agent, carrying the cooling energy generated by the refrigeration system to the areas requiring temperature control. During this process, the coolant remains in the same phase and does not undergo any phase change.

What Are The Common Types Of Refrigerant Used In Industrial Chillers?

• R23
• R404A
• R508B
• R507C
• R134A
• R407C
• R410A

What Are The Common Types Of Coolant For Industrial Chillers?

• 水
• Thermal oil (heat transfer oil)

Thermally conductive silicone oil is non-toxic, colorless, and odorless. When used under pressure in a closed system, its concentration needs to be monitored.

• Ethylene glycol-water solution

An ethylene glycol-water solution is a highly effective option for low-temperature control applications.

• Brine solution (saltwater solution)

Brine solutions—typically sodium chloride or calcium chloride in water—are highly corrosive. When used in a chiller system, special materials are required for the heat exchanger and pump to withstand the corrosion.

• Fluorinated oil (fluorinated fluid)

Fluorinated oil is non-flammable and is primarily used in the semiconductor industry. However, systems that use fluorinated oil typically involve higher investment costs.

• Ethanol

Ethanol has a high risk factor—it is flammable and potentially explosive. It is suitable for low-temperature applications and can be used in refrigeration systems down to -110°C (-166°F). When in use, the circulation pump must be properly sealed. If the volume used exceeds 500 liters, concentration monitoring is required.

• Liquid dichloromethane

When using liquid dichloromethane as a secondary coolant, the surrounding environment must be open and well-ventilated.

The Role Of Refrigerant And Coolant In Efficient Cooling

In a chiller system, the refrigerant moves through a closed-loop cycle. Inside the evaporator, it absorbs heat from the object being cooled and changes into a vapor. It then moves to the condenser, where it discharges the absorbed heat into the surrounding environment and transforms back into a liquid. The chiller’s refrigeration system relies on the phase changes of the refrigerant to achieve cooling.

The coolant, or cooling medium, is first cooled by the refrigerant in the evaporator. It is then directed to the cooling equipment, where it absorbs heat from the object being cooled, and subsequently returns to the evaporator to be cooled once more. This cycle continues to transfer cooling to the target environment.

In a refrigeration system, the refrigerant is essential—there can be a system without a coolant, but never without a refrigerant.