Refrigerants are essential working fluids in high-temperature heat pumps used in industrial process heat applications. They facilitate thermal energy transfer by evaporating at low temperatures, absorbing heat, then being compressed and condensing at a higher temperature level to release that heat. Selecting the appropriate refrigerant is crucial for the efficiency, safety, and environmental impact of a heat pump system.

Types of refrigerants

Synthetic refrigerants:

• HFCs (Hydrofluorocarbons): These refrigerants have moderate to high Global Warming Potential (GWP) and are increasingly being replaced by more environmentally friendly alternatives in industrial applications.
• HFOs (Hydrofluoroolefins): Modern synthetic refrigerants such as R1233zd(E) combine low GWP values with good thermodynamic properties. They are non-flammable and suitable for high-temperature applications up to 200°C.

Due to strict environmental regulations, the use of synthetic refrigerants is subject to increasing restrictions. Consequently, the industry is increasingly turning to innovative synthetic solutions with reduced GWP or natural refrigerants.

Natural refrigerants:

• Ammonia (NH₃, R717): Ammonia features excellent thermodynamic properties and high energy efficiency. It has zero ozone depletion potential (ODP = 0) and a very low GWP (~0). However, its toxicity and corrosiveness require strict safety measures.
• Carbon dioxide (CO₂, R744): CO₂ is non-toxic, non-flammable, and environmentally neutral. It operates at high working pressures and is particularly suitable for applications with temperatures up to 100°C.
• Hydrocarbons (e.g., Propane, R290): These refrigerants offer high energy efficiency and very low GWP. However, their flammability requires specific safety precautions.

Selection criteria for refrigerants

Choosing the right refrigerant depends on several factors:

• Temperature range: For applications above 100°C, refrigerants like ammonia or R1233zd(E) are particularly suitable.
• Pressure conditions: Refrigerants like CO₂ require specialized system designs due to their high operating pressures.
• Environmental aspects: A low GWP and zero ozone depletion potential are crucial for environmental sustainability.
• Safety requirements: Toxicity and flammability influence safety measures and handling procedures for refrigerants.