Heat transfer fluid contained in the collector loop

 Heat transfer fluid contained in the collector loop are :

 

WATER. As a heat transfer fluid, good quality water offers many advantages. It

is safe, non-toxic, chemically stable, inexpensive, and a good heat transfer medium.

Two drawbacks include a relatively high freezing point and a low boiling point.

Excessive scaling may occur if poor quality water is used.

 

GLYCOLS. Propylene or ethylene glycol is often mixed with water to form an

antifreeze solution. Propylene glycol has the distinct advantage of being nontoxic,

whereas ethylene glycol is toxic and extreme caution must be used to ensure that it is isolated from any potable water. For this reason, uninhibited USP/food-grade propylene glycol and water solution will be specified for any solar preheat system that requires an antifreeze solution.