HEAT PUMPS
Azeotropic and zeotropic: what’s the diff erence?
Aermec’s Barry Whyler weighs up the benefi ts of azeotropic and zeotropic refrigerants.
S Barry Whyler It is in
everyone’s interest to minimise their environmental impact, which has also been shown to be good for business.
electing the proper refrigerant is just as important as choosing the appropriate equipment for any application. Addressing factors such as global warming potential (GWP) and Ozone Depletion Potential (ODP), as well as minimising the environmental impact of equipment and processes, are mainstream topics. But how well do you know your azeotropic and zeotropic refrigerants, their diff erences, and the choices available for cooling and heat pump systems? Azeotropic and zeotropic refrigerants each off er their own advantages, and while they can both be used for chillers and heat pumps, several considerations need to be weighed. Examining the behaviour, performance, temperature glide, and coeffi cient of performance (COP), which can all vary depending on the specifi c azeotropic refrigerant and the system’s operating conditions, as well as the impact of leakages and maintenance concerns, are just some aspects to consider, along with availability and cost. Refrigerants can be either pure materials or blends. Examples of ‘pure’ compounds include R32 (replacement for R410a) and R717 (Ammonia). Blended refrigerants include a mixture of two or more refrigerants, for example, R407c (can be used as a retrofi t), which is a blend of R32, R125 and R134a. Blends were introduced to replace refrigerants that were being phased out as legal and environmental directives encouraged the use of lower GWP and ODP products. They are designed to match the properties of the refrigerants that were originally used. Categorising refrigerants as either azeotropic or zeotropic blends is determined by their respective boiling points and glide. Understanding the diff erences can signifi cantly impact the choice of equipment and refrigerant used.
Azeotropic refrigerants include two or more refrigerants that behave approximately as a single component because they have the same boiling point and condense at the same temperature. Zeotropic refrigerants are the most commonly used
refrigerants, particularly in retrofi t applications. Any refrigerant with an ASHRAE number in the 400 series is zeotropic (azeotropes are in the 500 series). These refrigerants are blends of two or more refrigerants, each with a distinct boiling point.
This means that the components in a zeotropic blend will boil and condense at diff erent temperatures, separating or spreading out unevenly – they fractionate from each other. If their components separate due to a leak or a temperature change, this can degrade a system’s effi ciency and overall system performance. System design must consider variations to achieve the desired optimal performance. Refrigerants and technologies are advancing at a faster
rate than ever before, and selecting the correct refrigerant is crucial for modern cooling and heat pump systems. There are many options and decisions centre on the application, conditions and environmental criteria to be addressed. Zeotropic blends off er fl exibility thermodynamically due to their temperature glide, which means that the boiling or condensing process occurs over a range of temperatures and not at a single point. The more volatile component vaporises fi rst, but during condensation, the less volatile component then condenses fi rst. Azeotropic refrigerants maintain a consistent composition
throughout evaporation and condensation, making their behaviour predictable, easier to manage, and operate, and can lead to a better-performing system. These features make azeotropic refrigerants attractive and make them a more reliable choice for a wide range of applications. In any HVAC system, stability is always the desired outcome. One of the most signifi cant advantages of azeotropic refrigerants is their single boiling point, while zeotropic refrigerants are aff ected by temperature glide. A consistent performance simplifi es heat exchanger design (no need to consider glide eff ects), and the minimal risk of composition changes is helpful. Their stability has a positive impact by reducing maintenance costs and potentially extending the system’s longevity, which can be a deciding factor and a practical choice when it comes to systems that require high dependability, such as chillers and heat pumps. Leakages are always to be avoided due to environmental
20 July 2025 •
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