A good heat transfer fluid is vital to the operation of a geothermal heat pump.
In most areas, geothermal contractors use a corrosion-inhibited antifreeze solution with a freeze point of 10 degrees or more below the minimum expected temperature.
The antifreeze solutions used are biodegradable, non-toxic, non-corrosive and have properties that will minimize pumping power needed.
Salts, such as calcium or sodium chloride, are safe, non-toxic and have good heat transfer properties, low cost and long life. However, they should be avoided in most applications because they are very corrosive and difficult to clean. Using salt fluids may void the warranties on some pumps.
Glycols, specifically ethylene or propylene, are relatively safe and generally non-corrosive, have fair heat transfer and medium cost. Their disadvantages are toxicity, viscousness at low temperatures requiring more pumping power, and a finite life.
Alcohol and water mixtures, including methyl (methanol), isopropyl or ethyl (ethanol), are relatively non-corrosive, have fair heat transfer and medium cost. Their disadvantages are flammability and toxicity.
- Potassium acetate was developed specifically for closed-loop geothermal systems as an environmentally-safe alternative to the three solutions above. It's safer, non-corrosive, non-toxic and more efficient. A disadvantage is a low surfaced tension.
Ordinary water can be used in warmer climates where the ground temperature stays warm and the heat pump's heat exchanger refrigerant temperature does not drop below freezing.
Learn more about: Selecting Loop Fluids