Zeotropic refrigerants are mixtures of several different chemical components which, unlike azeotropic refrigerants, do not evaporate or condense at a constant temperature. Instead, the phase change process occurs over a certain temperature range, known as "glide". This means that during evaporation or condensation, the components of the mixture can change their proportion in the vapour and liquid phases, which affects the operating parameters of the refrigeration or air conditioning system.
One of the main advantages of zeotropic refrigerants is the ability to tailor their properties by appropriately selecting the components of the mixture. This makes it possible to obtain parameters similar to those of phased-out refrigerants, such as R22, while simultaneously reducing environmental impact – for example, by lowering the ODP index (Ozone Depletion Potential). Many zeotropic blends, such as R407C, were designed specifically to replace older, more harmful gases.
The specific nature of zeotropic refrigerants means that handling them requires more attention than homogeneous refrigerants. Due to the different vapour pressures of the individual components, a leak can change the composition of the mixture, resulting in reduced equipment performance. In practice, this means that in the event of a refrigerant loss, it is recommended to completely empty the system and recharge it with a new, factory-made mixture. Additionally, the presence of "glide" requires accurate temperature and pressure measurements to correctly assess the system's operating state.
The most popular zeotropic refrigerants include:
(although the latter is technically a near-azeotropic mixture). They are used in air conditioning, heat pumps, refrigeration systems, and many other applications. The choice of a specific refrigerant depends on the technical requirements of the equipment, energy efficiency, and applicable environmental regulations.
Zeotropic refrigerants do not have a single specific "discoverer" in the sense of a person or date – they are the result of many years of research conducted by various teams of engineers and chemists in companies involved in refrigeration and air conditioning.
Their development gained significant momentum in the 1980s and 1990s, when ozone-depleting freons (like R12 or R22) began to be phased out as a result of the provisions of the Montreal Protocol. This was a period when the pro-ecological discourse essentially focused on the so-called ozone hole – much like how global warming is discussed today. At that time, manufacturers such as DuPont (now Chemours), Honeywell, or Arkema began developing gas mixtures to replace homogeneous refrigerants that were more environmentally friendly, focusing on the ecological threats as perceived at the time. Today, there is a partial return to single-component refrigerants or gases. For example, R32 – which is currently popular – is easier to handle and reclaim due to its homogeneity, so it's not a straightforward issue.
In practice, therefore, the "discovery" of zeotropic refrigerants is more of a technological and engineering process rather than a single discovery attributed to one person.
Zeotropic refrigerants play an important role in the modern HVACR industry, allowing for compliance with increasingly stringent environmental and technical standards. However, their use requires knowledge and precision to fully utilise their advantages and avoid operational problems.
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