Replacing fluorinated synthetic refrigerants has been the goal worldwide after their impact on global warming was discovered. For this reason, natural refrigerants have become the primary alternative in the refrigeration world. Among natural refrigerants, propane gas stands out for its excellent thermodynamic properties for producing cold.
What is propane gas?
Propane gas is a fossil hydrocarbon extracted from underground reservoirs. It is composed of a molecule formed by three carbon atoms and eight hydrogen atoms (C3H8). For this reason, this gas belongs to the group of organic natural refrigerants, unlike other inorganic natural substances such as ammonia and CO2.
Normally, propane gas is not extracted pure from reservoirs but comes mixed in LPG or natural gas. Therefore, in practice, propane is a byproduct of petroleum and LPG processing.
Main uses of propane gas
Until now, the main use of propane gas has been as boiler fuel to obtain heating and domestic hot water. It is also used in metal foundry furnaces. This gas is characterized by producing combustion with high calorific value, residue-free, and with very low CO2 emissions. For this reason, it is frequently used in welding copper pipes using copper-phosphorus-silver alloy rods.
Propane gas in refrigeration systems
Many people are familiar with propane gas because they use it as fuel in their boilers. However, few may be aware of propane’s potential as a refrigerant with excellent thermodynamic properties.
As a refrigerant, the ASHRAE standard assigns propane the code R-290. This code is interpreted as follows: the zero indicates that it does not have fluorine atoms. Furthermore, the nine represents the sum of hydrogen atoms plus one (8+1). Finally, the two in this code represents the carbon atoms minus one (3-1).
Thermodynamic properties of propane as a refrigerant
Propane successfully undergoes phase changes from gas to liquid, and vice versa, which every refrigerant gas must undergo in each refrigeration cycle. These phase changes occur within certain pressure and temperature parameters.
The characteristic pressure and temperature table of propane indicates that at a pressure of 9.6 psig, the temperature corresponds to -30 °C. If the pressure increases to 35.4 psig, the temperature reaches -10 °C. Then, when the pressure reaches 77.6 psig, the temperature reaches +10 °C. Increasing the pressure to 183.9 psig, the temperature reaches +40 °C. This curve of values is similar to the characteristics of the refrigerant R-22. For this reason, propane is used in refrigeration systems due to its high potential as a refrigerant substance.
Oils compatible with natural refrigerants
Refrigeration system compressors require good lubrication for a long lifespan. Therefore, when replacing fluorinated synthetic refrigerants with a natural refrigerant like propane, it is essential to use compatible lubricating oils. The most compatible oils for use with propane are alkylbenzenic (AB) and semisynthetic (M+AB).
Advantages of propane as a refrigerant
From an environmental perspective, propane gas does not harm the ozone layer. That is, it has an Ozone Depletion Potential (ODP) equal to zero (0). Additionally, it has a Global Warming Potential (GWP) equal to three (3). For example, for comparison, the synthetic refrigerant with the lowest GWP is R-134a, which has a value of 1430.
Propane is a stable substance and does not attack the materials typically used in refrigeration systems. Moreover, it is cheaper than any of the fluorinated synthetic refrigerants commonly used in the market. Additionally, it operates at relatively low pressures and temperatures, so its implementation does not require more robust materials or equipment.
It is worth noting that about 100 grams of propane provide the same refrigeration performance as 250 grams of another refrigerant in the same system. That is, with a propane charge of just 40%, the same refrigeration effect offered by other refrigerants is achieved.
Disadvantages of propane
The ASHRAE standard classifies propane gas as a highly flammable and low toxicity refrigerant. In this sense, according to ISO 817, propane is assigned the code A3. Therefore, the risk of fire is very high, even with small leaks. Consequently, this is the most important limitation for using this refrigerant in large industrial and commercial systems. For this reason, propane is only used in small domestic and commercial systems to date.
The maximum propane charge in a closed refrigeration system should not exceed 150 grams, as a safety standard. On the other hand, pure propane is an odorless gas, which makes leak detection difficult. However, there is the possibility of increasing the maximum charge to 1000 grams, complying with certain safety conditions in installations.
Intersam, a company specializing in the manufacture of evaporators and condensers
If you are considering replacing the refrigerant in your system with propane gas, it is important to ensure that you meet certain technical requirements. In this regard, at Intersam, we manufacture evaporators and condensers designed to work under the safety conditions required by each refrigerant. Therefore, do not hesitate to contact us if you need the services of a highly experienced and professional company in the field of refrigeration.