R744 is the designation for a refrigerant that is actually carbon dioxide, known from chemistry class as CO₂. Although it is primarily associated with a greenhouse gas, it has been used in refrigeration technology for over 100 years. In recent years, it has experienced a renaissance as an ecological alternative to synthetic refrigerants - more on that shortly. R744 belongs to the group of natural refrigerants and is classified as safe for the environment in terms of its impact on the ozone layer. We know that today, environmentally friendly refrigerants are being promoted - is that the only reason behind the growing popularity of R744?
The return of refrigerant R744 is mainly due to tightening environmental regulations, such as regulations concerning F-gases. Unlike many popular synthetic refrigerants, CO₂ has a very low GWP (Global Warming Potential) of 1. For comparison, many traditional refrigerants have a GWP of... even several thousand. This makes R744 exceptionally attractive in the context of ecology and future regulations. In practice, it virtually does not contribute to global warming.
R744 - that is, carbon dioxide - as a refrigerant, is characterized by specific properties that, however, somewhat distinguish it from other refrigerants - and this is not only about ecological considerations, which of course translate into easier promotion and commercialization, meaning simply easier market sales.
R744 operates at very high pressures – significantly higher than popular HFC refrigerants. It also has a low critical temperature (approx. 31°C), which means that in many applications it operates in so-called transcritical systems. Thanks to its high volumetric density, it allows the use of smaller installation components.
The operation of refrigerant R744 at higher pressures can be an advantage in some situations. However, it can also be a disadvantage - because it may require equipment adapted to its requirements. This refers to condensers or freon heat exchangers intended to work with it, but also to smaller system components. Carbon dioxide can therefore perform well, but it requires knowledge of its parameters, because although it is quite cheap in itself - it may have certain requirements.
R744 finds wide application in modern refrigeration and heating installations - but rather in specific specifications. It is used in:
It is also increasingly used in refrigerated transport and heat recovery systems, but it seems that, due to pro-ecological trends, it still has a significant future ahead. Development work in the industry is focusing on the wider use of refrigerants like R744 - i.e., those with a sufficiently low GWP and an appropriate ODP coefficient (which for R744 is 0).
They are mainly pro-ecological, but not only. The most important advantages of R744 include:
Thanks to these features, R744 is considered one of the most future-proof refrigerants, especially if the pro-ecological approach continues, as we can already see that we are on the verge of reducing the most radical ecological assumptions, not only in Europe but also around the world.
Despite many advantages, R744 also has its limitations. The biggest challenge is the aforementioned high operating pressures, which require the use of specialized components and appropriate safety measures, proper soldering of components, etc. Additionally, the efficiency of transcritical systems can decrease in high ambient temperatures. This requires the use of advanced solutions, such as gas cooling or hybrid systems.
R744 is a non-flammable refrigerant and considered safe - after all, we know what carbon dioxide is. However, at high concentrations, it can pose a certain health risk (because it displaces oxygen). Therefore, installations must be properly designed and equipped with CO₂ detection systems. It is also crucial to comply with standards and ensure proper training for installers.
Everything indicates that the role of R744 will likely continue to grow. In the face of global climate change and regulations limiting the use of F-gases, natural refrigerants are gaining importance. R744, thanks to its properties, has great potential in the further development of refrigeration and heating technologies.
R744 is a modern, ecological, and increasingly used refrigerant. Although the word "modern" in reference to the long-known carbon dioxide - we put in quotation marks. Despite certain technical challenges, its advantages make it one of the key directions for the development of the HVAC industry. It is worth getting to know its specifics today and preparing for its increasingly widespread use in the future.
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