Our installers often ask why we recommend a 25% mixture of propylene glycol to water for geothermal loopfields.
Propylene glycol at a 25% mixture by mass yields a freezing point of about 12.5 degrees F. Since propylene glycol is slightly more dense, 1.036 g/cm3 to 1.0 g/cm3 for water, this equates to a mixture by volume of 25% freezing at 12.95 degrees F. 20% by mass freezes at 18 degrees F. This is sufficient for interior hydronic lines.
Our pump sizing is based on the viscosity of a 25% glycol mixture by volume. We use this mixture because it uses the minimum amount of glycol for pumping viscosity losses while providing freeze protection.
The reynolds number also plays a part in the ratio. The greater the volume of the thicker glycol, the faster you have to pump to reach turbulent flow. Use 25% glycol to 75% water with our product in a correctly designed geothermal loop field for optimum performance.
Since our product is inhibited, it has a glycol ratio of 96%. Four percent is the additives for corrosion resistance and the anti-foaming agent. This is the highest ratio available in this type of glycol. Some products labeled -100 can be as low as 65%. If you mix that at 25% you would actually be only 16.25%.
Download the Freeze Safe 100 PDF Spec Sheet for more information.
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Tags: geothermal, glycol, loop field
[...] This “Hot Box” solution allows for two things. First, it allows the heat pump to be placed in a conditioned space for optimal performance and efficiency. Secondly, it allows the attic to remain unconditioned to conform to the outdoor temperature. This is important, especially in winter, if ice damage is a concern. Also, the attic will not be comfortable in the winter and then uncomfortably warm in the summer. It is also important to note that piping from your geothermal loopfield to the heat pump must be insulated and contain the correct propylene glycol mixture for geothermal systems. [...]
[...] to the pump and then connect the pump to the other fitting on the pump panel. Mix water with the propylene glycol that you purchased with your geothermal loop field. The proper ratio is 25/75 fluid to water [...]