Isopropyl Alcohol as anti-freeze agent ?

by **powerboatman1** » Sat Oct 31, 2009 9:18 am

Geoexchange newbie here. I'm installing a horizontal ground loop based system, and was wondering about using isopropyl alcohol as anti-freeze ? I have a large quantity of anhydrous isopropanol available. Also, what is being used as an anti-corrosive in the loop ?

That's the great thing about being a DIYer, you learn all sorts of new things.

Thanks, Dave S.

by **gabby** » Sat Oct 31, 2009 12:39 pm

From the In-ground concrete tank thread:

Depending on burial depth and type of soil, horizontal and "slinky" ground loops may be subject to seasonal temperature swings of ±10 ºF, and in such cases the late-winter, natural ground temperature would drop below 50 ºF. The heat extraction process can lower the soil temperature in the immediate vicinity of the ground loop by a further 10 ºF, such that the water leaving the ground loop would approach or even fall below 40 ºF. For submerged closed loops, ponds or lakes that freeze at the surface during the winter can have bottom water temperatures below 40 ºF; also creating a condition that would require antifreeze protection.

Solutions of alcohols in water - methanol and ethanol - have low viscosity (which translates to lower pumping power) and relatively high heat transfer capability (which translates to shorter ground loops). On the negative side, however, they are highly volatile, flammable in concentrated or pure form, and toxic. Once mixed with water in typical antifreeze concentrations, the resulting solution is not flammable. Unlike methanol, pure ethanol is not toxic, but only denatured ethanol can be purchased for commercial use as an antifreeze. Denaturants render the ethanol toxic and some denaturants also will chemically attack polyethylene piping. Methanol is preferred because it eliminates the possibility of such damage to ground loop piping, even though it is more toxic than denatured ethanol.
• Compared with pure water at 40 ºF, the poorer heat transfer capability of propylene glycol can lead to a 10-15% increase in loop length, depending on the level of antifreeze protection, whereas methanol has less than a 5% impact for the same heating or cooling capacity.
• Again compared with pure water at 40 ºF, the higher viscosity of propylene glycol, in combination with the longer loop required for a given system capacity, can increase pumping power requirements by 35-40%, depending on the level of antifreeze protection, whereas methanol entails only a 15-25% pumping power increase.
• Finally, for a given level of antifreeze protection, the cost of propylene glycol is ten times greater than that of methanol, typically in the range of tens of dollars per ton of system heating or cooling capacity, compared with dollars per system ton for methanol solutions'

Ethylene glycol is the most widely used automotive cooling-system antifreeze, although methanol, ethanol, isopropyl alcohol(rubbing alcohol), and propylene glycol are also used. Substances that inhibit corrosion are usually added; antifoaming agents are sometimes added as well. In automotive windshield-washer fluids, an alcohol (e.g., methanol) is usually added to keep the mixture from freezing; it also acts as a solvent to help clean the glass.
Methanol and isopropyl alcohol are normally used in dry gas. Most commercial antifreezes have an additive to make them bitter to the taste.