Closed Loop System Freeze Protection

When air temperatures plummet, frost and freezing protection of closed loop systems is of the utmost importance. Most commonly glycol (antifreeze) is added to the system to provide the necessary protection.

Glycol based water solutions are commonly used in heat-transfer closed loop systems, where the temperature in the heat transfer fluid can be below 0oC and therefore cause freezing and damage to the integrity of the plant.

Ethylene Glycol is the most common antifreeze fluid for standard heating and cooling applications. If there is a risk of human ingestion, Propylene Glycol which is food safe, should be used.

Protection from freezing is imperative when a system requires pumping. It is achieved when the glycol concentration in a system is sufficient to prevent ice crystals from forming when the fluid experiences its lowest temperature.

The chart below under gives an idea of how the freezing point is lowered when Ethylene Glycol or Propylene Glycol (Food safe) is added to water systems.

Percentage Ethylene Glycol Freezing point temperature Percentage Propylene Glycol Freezing point
0% 0°C 0% 0°C
10% -3°C 10% -3°C
20% -8°C 20% -8°C
30% -16°C 30% -14°C
40% -25°C 40% -22°C
50% -37°C 50% -34°C
60% -55°C 60% -48°C

Specific heat capacity, viscosity and specific weight of a water and Ethylene Glycol solution will vary significantly with the percentage of Ethylene Glycol and the temperature of the fluid. Indeed properties differ so much from clean water, that heat transfer systems with Ethylene Glycol should be calculated thoroughly for actual temperature and solution.

HBE can help with the following services:

  • Initial surveys of closed loop systems to determine the water chemistry and from that, decide on an appropriate plan of action.
  • Supply of both propylene & monoethylene glycol.
  • Dosing the chemical into the system.

If you require any further information or help with your freeze protection or Glycol dosing, call 0845 6399673 or email us at

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