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What is the recommended minimum heat transfer fluid concentration?

Many questions have been raised about the recommended minimum glycol concentration of 25-30%, as stated in Dow’s product literature. For Example, if a system only requires freeze protection to 20 degrees F (7 degrees C) and this can be achieved with 18-20% glycol, why should at least 25% be added?

There are several reasons for the recommended minimum concentration. The first is corrosion protection. DOWFROST glycol-based heat transfer fluids are designed to work in both heating and cooling systems at a wide range of concentrations. For this to work successfully, the starting fluid must have the right balance of inhibitors in order to maintain proper corrosion protection at various concentrations. The inhibitors are formulated to give optimum performance and fluid lifetime at glycol levels between 25 and 60%. Reducing the glycol concentration below 25% reduces the inhibitor concentration to a level that may not provide adequate corrosion protection for a system.

The second reason is the stability of the fluid. Both ethylene and propylene glycol break down on exposure to high temperatures. With a higher concentration of DOWFROST there is also a greater concentration of inhibitor present in the solution. The higher level of inhibitor provides more buffering for any organic acids that may be formed due to glycol degradation.

The third reason for using at least 25% glycol in the system concerns the possibility of bacterial growth. With concentrations at or above 20% both ethylene and propylene glycol inhibit the growth and proliferation of most microbes and fungi. The reduced surface tension in the glycol solution interrupts the cell walls of bacteria, resulting in an environment that will not support bacterial growth. At very low glycol concentrations, for example 1% both ethylene and propylene glycol act as a nutrient for bacteria. At these concentrations, bacteria will biodegrade the glycol causing rapid growth of bacterial contamination. At levels above 1 and below 20% some bacteria can survive with limited growth, especially at moderate temperatures.

Certain applications, such as ground source heat pumps, call for a 20% glycol solution. These systems typically consist of plastic piping and are operated at fairly low temperatures, which helps to minimize corrosion effects. For these situations, it is recommended to use DOWFROST HD containing a stronger corrosion inhibitor package and should maintain adequate corrosion protection at 20% glycol concentrations.

Be sure to make the right choice for your next glycol order. Choose DOWFROST™ Heat Transfer Fluids now available in exactly the volumes you need including 1 gallon, 5 gallon, and 55 gallon containers. Contact Lentus today to learn more.

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