- Ethylene glycol, if the system did not
need to have a nontoxic fluid. Ethylene glycol is the cheapest and most
efficient, so it is the first choice where it can be used.
- Propylene glycol, which would be chosen for other heat transfer fluid application using glycol-based fluids.
First, the "green" element is considered in many new applications. If the system is a renewable energy system such as solar or geothermal, then there is a tendency to use a renewable fluid.
Second, the long-term usage aspect (better fluid life) plays a part as well. With bio-based glycols degrading more slowly than the other glycols, it may be the choice for systems requiring long life without changing the fluid for many years and reducing overall maintenance cost.
Finally, the user must consider cost. Ethylene glycol will be the least expensive, but it has limitations. Propylene glycol is a good choice if there is a need for a safe, nontoxic fluid that is less expensive than a bio-based glycol or the renewable propylene glycol.