Which heat transfer fluid should be used in a pressurized system?


For a pressurized installation, do not use water from the municipal distribution system, as it contains chlorine which causes corrosion of metals and therefore of the heat exchanger of the panel (in the case of the Wave and SPRING4 panel only), as well as the metal parts of the solar circuit in the machine room (copper fitting, brass, valves, the exchanger tank, etc). The use of mains water in the closed circuit can accelerate the formation of sludge in the circuit.

The heat transfer fluid must be a mixture of glycol and demineralized water. We cannot guarantee an installation that has not been commissioned with demineralized water.

Consequently we recommend using a pre-mixed glycol solution, which already contains demineralized water as well as antioxidants.

Physical characteristics of glycol

The physical characteristics of the mono propylene glycol generally available from our distributors are presented in this table:

Glycol concentration

(% of volume)







Specific heat at 20°C








Volumique mass at 20°C








The percentage of glycol contained in the heat transfer fluid varies depending on the region. In France, it is required by law that the installer comply with the requirements of ENN1991 1-6 clause, which indicates the minimum temperature to be taken into account. 

Note on Glycol lifetime

SPRING panels have the advantage of having a stagnation temperature of 90°C, which is low compared to simple thermal panels. Thanks to this, the glycol is not overstressed and is not a victim of the caramelization effect, known in the case of thermal panels.

To date, our facilities over 10 years old have not needed glycol renewal.


The case of SPRING4

The type of glycol used in our panels is carefully characterized to guarantee optimum corrosion resistance. This characterization, carried out by CETIM, recommends the use of clean (distilled) water for glycol dilution and the presence of corrosion inhibitors in the glycol. It must also be thermally stable for operating temperatures ranging from -40°C to +80°C.

For systems containing copper, we recommend TYFOCOR because of its low corrosivity towards aluminum. For copper-free installations, TYFOCOR L is also suitable, although slightly more corrosive. Other products such as FRIOGEL® NEO, NEUTRAGEL® NEO and GREENWAY® NEO N have shown slightly higher mass losses, without any indication of their thermal stability.

To know more click on the following article : How is calculated the glycol volume and ratio in the software MyDualsun ?