How is heat transfer fluid protected from the outside environment when shared between solar heat collection and a boiler?

The correct choice is to add a compatible glycol to the heat transfer fluid used between solar heat collection and a boiler. Glycol, specifically propylene glycol or ethylene glycol, serves as an effective antifreeze agent. This is crucial because it lowers the freezing point of the fluid, thus preventing it from freezing in colder temperatures where solar collectors might operate. In addition, glycol has corrosion-inhibiting properties that help protect the heat transfer system from degradation due to exposure to environmental factors.

While other methods of protection exist, such as insulating pipes to reduce heat loss or implementing pressure regulators to maintain system integrity, these approaches primarily focus on energy efficiency and pressure management rather than directly protecting the heat transfer fluid. Adding glycol specifically tackles the problem of fluid stability and integrity against environmental challenges, particularly in varying temperature conditions, which emphasizes its role as the most effective choice for protecting the heat transfer fluid in this context.