Varmeoverføringsmedium

Varmeoverføringsmedium, or heat transfer medium, is a substance used to move thermal energy within heating and cooling systems. It circulates between a heat source and a heat sink, absorbing or releasing heat as its temperature changes. The choice of medium depends on operating temperature and pressure, chemical compatibility with system materials, safety, and cost.

Common liquids include water and water-based solutions (glycol-water blends for freeze protection), mineral oils or synthetic oils for higher temperatures, and specialized thermal fluids. Gases such as steam or refrigerants are used in closed cycles where phase change enhances heat transfer. Phase-change materials store and release large amounts of energy at specific temperatures, useful for storage and load leveling.

Key properties for selecting a medium are specific heat capacity, thermal conductivity, viscosity, freezing and boiling points, chemical stability, and compatibility with system components. Safety and environmental considerations include flammability, toxicity, and ecological impact, as well as required pressure and containment. The medium should minimize corrosion and fouling and be chosen to reduce pumping power and energy losses.

Applications span district heating and cooling, industrial process heat, refrigeration cycles, solar thermal collectors, geothermal systems, and heat exchangers in chemical plants. In many installations, water serves as the default medium; glycol-water blends provide freeze protection; heat transfer oils cover higher temperatures; refrigerants enable vapor-compression cycles; and phase-change materials enable latent heat storage. Maintenance involves monitoring for leaks and contamination and regular checks of concentration, pH, and viscosity to ensure efficient transfer.