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Glycol Circuit, What is glycol circuit, How does a glycol circuit work

Glycol circuit speaks to what is a glycol circuit and how does a glycol circuit work within a building heating system.

This circuit presents mechanical equipment that would be included on the heat exchanger secondary circuit.

Circuit Circulating Pumps

The purpose of the circuit pumps is to provide a mixture of glycol and hot water through the secondary side of the heat exchanger to heating components throughout the building.

Circuit Charging Tank

The circuit charging tank provides a means to charge the heating system heating system glycol circuit when necessary. Fluid may be stored in a tank under a higher pressure than the operating pressure of the system.

It is pumped into the heating system when necessary to add to the system. It will be a mixture and the higher percentage solution the greater the protection from freezing of the system.

Glycol Makeup System

The automatic makeup system consists of:

  • makeup valve.
  • shut off valves.
  • pressure reducing valve.

    One side of the system is connected to the pressurized charging tank and the other is connected to the line from the heating system to the expansion tank. The pressure reducing valve maintains a constant pressure on the heating system by allowing fluid to enter the system to the expansion tank.

    The pressure reducing valve maintains a constant pressure by allowing fluid to enter the system when the system pressure drops below the pressure reducing valve setting.

    The shut off valves are used to isolate the the PRV should it malfunction. The bypass valve is opened manually to add solution whenever the expansion tank level drops too low.

    Expansion Tank

    The circuit expansion tank allows for fluctuation in the volume of fluid as the temperature changes. The expansion tank size is as designed to allow for full operating temperature ranges in the glycol.


    The pressurization serves three purposes:

  • maintains the circuit at design pressure.
  • provides a positive head on the suction side of the
  • circulating pump ensuring air is not drawn in through the
  • automatic vents.
  • saves wear and tear on the pump during start up.

    Building Heating Systems

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