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Which coolant should you choose for a low-temperature cooling system

The choice of a coolant is based on the minimum operating temperature in the system, the fluid viscosity at low temperatures, toxicological requirements, equipment materials, and the design of the circuit.

In general:

potassium formate is considered for low-temperature industrial systems where minimal viscosity increase during cooling is essential;
ethylene glycol is used in sealed technical circuits where contact with drinking water, food products, people, or animals is impossible;
propylene glycol is selected where higher safety requirements apply, although its viscosity increases significantly at low temperatures;
glycerin can also be used as a coolant base, but its viscosity rises rapidly as the temperature decreases.

In this article, the values −20, −32 and −60 °C used for FREEZLIGHT products indicate the crystallization onset temperature. This is the temperature at which the first crystals begin to form, not the recommended continuous operating temperature.

What Is a Coolant?

A coolant is a liquid that circulates between refrigeration equipment and cooling consumers.

It can transfer cooling capacity to:

freezing chambers;
cold storage facilities;
process heat exchangers;
production lines;
cooling tanks;
secondary chiller circuits;
ice rinks.

A coolant is not the primary refrigerant used in a refrigeration system. Potassium formate, glycol, and glycerin solutions circulate in a separate circuit and do not replace refrigerants such as Freon, ammonia, carbon dioxide, or any other refrigerant specified by the equipment manufacturer.

Information Required Before Choosing a Coolant

Before comparing different coolant bases, determine the following:

The minimum coolant temperature in the circuit.
The maximum operating temperature during operation, shutdown, or defrosting.
The type of system: closed or open, primary or secondary.
The materials of pipes, heat exchangers, pumps, seals, and soldered joints.
The characteristics of the circulation pump.
The toxicological requirements for the facility.
The fluid previously used in the system.
Whether the circuit can be completely drained and flushed.

The most important parameter is the temperature of the coolant itself. The air temperature inside a chamber or room may differ from the coolant temperature near the evaporator or in individual sections of the pipeline.

Why Viscosity Matters

Viscosity indicates how easily a liquid flows through a piping system.

As the temperature decreases, all coolant bases discussed in this article become more viscous, although the rate of viscosity increase differs considerably.

The higher the viscosity, the:

greater the hydraulic resistance;
higher the load on the pump;
lower the possible flow rate through the circuit;
more difficult the system startup after deep cooling;
greater the power consumption required for circulation;
higher the risk of insufficient flow through the heat exchanger.

Therefore, comparing viscosity values only at +20 °C is not sufficient. The viscosity at the actual minimum operating temperature is what really matters.

How the Viscosity of Different Coolant Bases Changes

The following example is based on official technical data for three commercial coolants with approximately the same crystallization onset temperature (about −30…−32 °C).

These values are not the characteristics of FREEZLIGHT products and should not be considered proof that different products are interchangeable. The table simply illustrates the general differences between the coolant bases.

Coolant Base and Example Solution	+20 °C, mm²/s	0 °C, mm²/s	−20 °C, mm²/s	−30 °C, mm²/s
Potassium formate	1.79	2.74	5.36	8.35
Ethylene glycol	3.62	7.75	21.1	39.0
Propylene glycol	6.08	17.6	80.2	211

According to these data, when the temperature drops from +20 to −20 °C:

the potassium formate solution becomes approximately 3 times more viscous;
the ethylene glycol solution becomes approximately 5.8 times more viscous;
the propylene glycol solution becomes approximately 13.2 times more viscous.

When the temperature drops from +20 to −30 °C:

the potassium formate solution becomes approximately 4.7 times more viscous;
the ethylene glycol solution becomes approximately 10.8 times more viscous;
the propylene glycol solution becomes approximately 34.7 times more viscous.

Among these examples, the potassium formate coolant demonstrates the smallest increase in viscosity, while the propylene glycol solution shows the largest.

The exact values depend on concentration, formulation, additive package, and crystallization onset temperature. When designing a specific system, always use the technical data for the exact product to be filled into the system.

How Glycerin Behaves During Cooling

For comparison, let’s look at how the dynamic viscosity of a 60% aqueous glycerin solution changes with temperature.

+20 °C — approximately 10.8 mPa·s;
+10 °C — approximately 17.4 mPa·s;
0 °C — approximately 29.9 mPa·s.

This means that the viscosity increases by almost 2.8 times when the temperature drops from +20 to 0 °C and continues to rise rapidly as the temperature decreases further.

It is not appropriate to compare the absolute viscosity values of glycerin with those shown in the previous table because different test methods and measurement units are used. However, the overall conclusion remains the same: glycerin is not considered a low-viscosity base for low-temperature cooling systems.

Potassium Formate Coolant

Potassium formate is primarily used in closed secondary industrial and process cooling circuits.

Its main practical advantage is a relatively small increase in viscosity during cooling compared to most glycol-based solutions with a similar crystallization onset temperature.

Such products are commonly used in:

freezing chambers;
low-temperature cold storage facilities;
industrial refrigeration systems;
secondary chiller circuits;
quick-freezing systems;
long pipeline networks;
systems with multiple cooling consumers.

Before use, the compatibility of equipment materials should be verified, particularly galvanized components, aluminum alloys, soldered joints, seals, and internal protective coatings.

FREEZLIGHT® Frost −60 °C is based on potassium formate and is intended for closed secondary industrial and process cooling circuits.

Ethylene Glycol Coolant

Ethylene glycol is widely used in sealed technical heating, air conditioning, and cooling systems.

At low temperatures, its viscosity increases more than that of potassium formate but less than that of propylene glycol.

The primary limitation of ethylene glycol is its toxicity.

Therefore, it is not used in:

open systems;
systems with open expansion tanks;
domestic hot water and potable water systems;
food processing facilities where contact with food products is possible;
locations where leaks may be accessible to people or animals.

The FREEZLIGHT product line includes ethylene glycol coolants with crystallization onset temperatures of −20 °C and −32 °C for use in sealed technical systems in accordance with the equipment manufacturer’s recommendations.

Propylene Glycol Coolant

Propylene glycol has lower toxicity than ethylene glycol and is therefore used in systems with higher safety requirements in the event of accidental leakage.

However, it is characterized by a significant increase in viscosity as the temperature decreases.

For this reason, the following should always be verified before use:

pump starting capability;
flow rate through the heat exchanger;
pressure loss;
pipeline diameter;
drive power;
maximum allowable viscosity specified by the equipment manufacturer.

The FREEZLIGHT product line includes propylene glycol coolants with crystallization onset temperatures of −20 °C and −32 °C, selected according to the operating temperature range, system design, and equipment manufacturer’s recommendations.

Glycerin-Based Coolant

Glycerin-based coolants are also used in certain heating and cooling systems.

When selecting this type of coolant, its relatively high viscosity and the significant increase in viscosity at low temperatures should be taken into account.

A commercial coolant should not be evaluated solely by the properties of pure glycerin or selected simply because of its natural origin. The performance of a finished coolant is determined by its complete formulation, concentration, and additive package.

A Brief Comparison of Different Coolant Bases

Criterion	Potassium Formate	Ethylene Glycol	Propylene Glycol	Glycerin
Typical applications	Industrial low-temperature cooling	Sealed technical systems	Systems with increased toxicological safety requirements	Selected heating and cooling systems
Viscosity increase during cooling	The lowest among the examples presented	Moderate	The highest among the examples presented	Significant
Main limitation	Material compatibility must be verified	Toxicity	High viscosity at low temperatures	High viscosity at low temperatures

How to Choose a Coolant

Determine the minimum coolant temperature.
Select the required crystallization onset temperature with an appropriate safety margin.
Consider the toxicological requirements of the system.
Check the allowable viscosity at the minimum operating temperature.
Verify the compatibility of construction materials.
Find out which fluid was previously used in the system.
Before replacing one coolant base with another, drain and flush the system as completely as possible.
Review the technical documentation for the specific product.

Selecting a coolant based only on its crystallization onset temperature is not sufficient. All characteristics of the specific system, as well as the equipment manufacturer’s recommendations, should be taken into account.

Who Is Responsible for Coolant Selection?

The Knowledge Center materials help compare different coolant bases and explain their key characteristics.

The final product selection should always take into account:

the operating temperature range;
the system design;
the hydraulic calculation;
equipment materials;
the equipment manufacturer’s requirements;
operating conditions.

System filling, commissioning, and maintenance should be carried out by qualified specialists.

Novohim LLC supplies products in accordance with their technical documentation but does not perform the functions of a design, installation, or service organization.

Common Mistakes

Selecting a coolant based only on its crystallization onset temperature.
Ignoring the increase in viscosity at low temperatures.
Comparing properties only at +20 °C.
Evaluating a commercial coolant based on the properties of the pure substance.
Mixing different products without verifying compatibility.
Ignoring residues of the previous coolant after flushing.
Filling a complex system without following the equipment manufacturer’s requirements.

Related FREEZLIGHT Products

FREEZLIGHT Frost −60 °C Based on Potassium Formate

A low-temperature coolant containing at least 50% potassium formate, designed for closed secondary industrial and process cooling circuits.

Recommended anchor:

FREEZLIGHT Frost −60 °C potassium formate coolant

FREEZLIGHT −32 °C Based on Ethylene Glycol

A coolant designed for sealed technical systems where contact with drinking water, food products, people, or animals is excluded.

Recommended anchor:

FREEZLIGHT −32 °C ethylene glycol coolant

FREEZLIGHT −32 °C Based on Propylene Glycol

A coolant for systems with increased toxicological safety requirements. When used in cooling systems, viscosity and pump performance should be verified.

Recommended anchor:

FREEZLIGHT −32 °C propylene glycol coolant

FAQ

Which coolant base shows the smallest increase in viscosity during cooling?

Among the specialized solutions compared, potassium formate demonstrates the smallest increase in viscosity.

Which becomes more viscous: ethylene glycol or propylene glycol?

At similar temperature levels, a propylene glycol solution becomes significantly more viscous than an ethylene glycol solution.

Where does glycerin fit into this comparison?

Glycerin also has high viscosity that strongly depends on temperature. The exact comparison with propylene glycol depends on concentration, but glycerin is not considered a low-viscosity base for deep cooling applications.

Should you always choose the lowest crystallization onset temperature?

No. An adequate design safety margin is sufficient. An excessively concentrated product may increase viscosity and pump load.

Can potassium formate be mixed with glycol?

No, not without verifying compatibility.

Can ethylene glycol be used in food processing facilities?

It is not used in systems where contact with food products, drinking water, or process water is possible.

Is propylene glycol completely safe?

No. It has lower toxicity than ethylene glycol, but a commercial coolant remains a technical fluid.

Who should fill the system?

The system should be filled by a qualified specialist or service organization familiar with the system design, responsible for system preparation, pump verification, air removal, and equipment commissioning.