Basically, refrigerant gases used in all refrigeration systems are classified as natural and synthetic. Ammonia and carbon dioxide are the most widely used natural refrigerants due to their excellent thermodynamic properties. On the other hand, fluorocarbon-based refrigerants are synthetic substances, which began to be developed and produced in the 1930s.
In this post, we will talk about the characteristics and applications of the main natural and synthetic refrigerants that are used today.
Importance of refrigerant gases in refrigeration systems
The thermodynamic properties of refrigerant gases are the essence of the operation of any refrigeration system. Therefore, the design and construction of the compressor, evaporator, condenser, and expansion valve determine the type of refrigerant to be used.
Refrigerants are substances with a high capacity to absorb heat from one place and then dissipate it elsewhere. In this sense, the absorption of heat is carried out by taking advantage of the low temperature that the refrigerant acquires, in low-pressure conditions. On the other hand, heat dissipation is carried out thanks to the ease of the coolant heating up, under high-pressure conditions.
In both industrial and domestic and commercial refrigeration, refrigerant gases move through a circuit. This circuit has a low-pressure zone and a high-pressure zone, in which the refrigerant is cooled and heated, respectively.
Natural refrigerant gases
The most important natural refrigerant gases for industrial refrigeration are ammonia (NH3) and carbon dioxide (CO2). In addition, we must also highlight sulfur dioxide (SO2), which was used at the beginning of the 20th century in small refrigeration equipment. Next, we will talk about each of them and also about propane gas.
Ammonia is the most widely used refrigerant for cooling large cold rooms, since 1876. The ASHRAE classification assigns ammonia the code R-717. This is a highly toxic and corrosive gas. Therefore, refrigeration installations that use this refrigerant must comply with strict safety measures.
With ammonia, temperatures as low as -70 °C can be reached in refrigeration plants by absorption. On the other hand, using mechanical compression systems, temperatures of -40 °C can be reached. Ammonia refrigeration evaporators work at an average pressure of 20 psig, while condensers work at about 155 psig.
On the other hand, the boiling point of ammonia at atmospheric pressure is -33 °C, but the critical temperature is 133 °C. Also, the freezing temperature of ammonia is -78 °C.
Ammonia has an ozone depletion potential (ODP) equal to zero (0). On the other hand, the global warming potential (GWP) of ammonia is also zero. All the mentioned characteristics make ammonia an excellent natural and ecological refrigerant.
Carbon dioxide, also known in the ASHRAE standard as R-744, is a much less toxic and corrosive refrigerant gas than ammonia. However, the use of its thermodynamic qualities is achieved at higher working pressures. Consequently, it requires more robust compressors, evaporators for refrigeration, condensers, and pipes.
CO2-based industrial refrigeration systems work in a subcritical or transcritical regime, although the latter requires relatively more complex installations.
In the mid-1930s, sulfur dioxide (SO2) was used as a refrigerant gas in small domestic refrigerators. However, it was rapidly displaced by chlorofluorocarbon-based synthetic refrigerant gases. The main causes for such substitution were its high toxicity and corrosivity.
Propane is a refrigerant gas derived from petroleum and has excellent thermodynamic properties. Its main disadvantage is that it is highly flammable, which requires taking certain safety conditions in case of leaks. However, it has the advantage of having a very low price.
In the ASHRAE nomenclature, propane is known as R-290 and is widely used in industrial refrigeration systems. In addition, it is a refrigerant gas with a PAO equal to zero and a GWP of just 3. Therefore, it is a very ecological alternative.
Synthetic refrigerant gases
By 1930, refrigeration companies understood that natural refrigerants were never going to allow them to expand refrigeration to homes and small businesses. In other words, apart from the high toxicity and corrosiveness of almost all natural refrigerants, their characteristics did not allow compact equipment to be built. Consequently, thanks to a great research and development effort, the first synthetic refrigerants emerged.
For the time, these new coolants were the closest thing to the ideal coolant. In this way, dichlorodifluoromethane (CCl2F2) was created, which is also known in the ASHRAE standard as R-12. However, over the years it was determined that fluorocarbon-based refrigerants were damaging the ozone layer and contributing to global warming. Consequently, in the Montreal Protocol (1986) its replacement was agreed upon at the global level.
R-12 was replaced by chlorodifluoromethane (HCFC), which is also known as R-22. However, this synthetic refrigerant gas was quickly replaced by a new generation of HFC (hydrofluorocarbon) gases, which cause less harmful effects to the environment.
R-134a, one of the most used HFC gases today
This HFC refrigerant has zero ozone depletion potential (ODP). On the other hand, the global warming potential (GWP) is 1430. When R-134a is used in compressors designed for R-12, mineral oil must be replaced by synthetic oil based on polyester (POE).
R-134a can in turn be replaced by a more modern gas based on hydro-fluoro olefins (R-513A). This state-of-the-art refrigerant gas has a GWP of 630, which is much lower than that of R 134a.
R-152a for industrial refrigeration
R-152a is a difluoroethane-based refrigerant gas, which has a GWP of 124 and does not destroy the ozone layer. This refrigerant has thermodynamic properties superior to R-134a, and is widely used in chiller-type refrigeration systems.
Zeotropic mixtures of refrigerant gases
All the refrigerants mentioned above are chemically pure substances. Therefore, they have a single boiling and condensation point, at a certain pressure and temperature. However, zeotropic refrigerant mixtures are compounds formed by two or more pure refrigerants, with different boiling and condensation points. These mixtures form the 400 series of the ASHRAE classification.
The most widely used zeotropic mixtures today are the following: R-404A, R-410A, R-450A, and R-448A. In all of them, the slip produced by the different boiling and condensation points of the substances that make up each mixture is taken into account.
Intersam, a company specialized in condensers and evaporators for commercial and industrial refrigeration
The new environmental regulations are increasingly strict to achieve the definitive substitution of fluorocarbons and HFC gases in refrigeration systems. Therefore, you must first study the changes necessary to adopt the new synthetic or natural refrigerant gases. These changes not only affect the evaporator, but also the condenser, compressor, pipes, etc. For this reason, you will need a specialized company such as Intersam, which can advise you on the condenser and evaporator.