Refrigerant gases

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What are refrigerant gases?

Refrigerant gases are transport fluids that carry heat energy from the low temperature level – evaporator – to the high temperature level – condenser – where they can dissipate their heat.

These refrigerant gases are the refrigerating fluid contained in a refrigeration system and whose mission is to absorb heat from the cold source at low pressure and temperature and to transfer it to the hot source at high pressure and temperature. All this with the corresponding variations of state from liquid to vapour and from vapour to liquid.

Basic characteristics of the refrigerant gases

Refrigerant gases are noted for having a low boiling point, a low dew point and additionally the highest possible critical point to make the evaporation process more efficient.

Characteristics that define a refrigerant

• Low boiling temperature: A boiling point below room temperature, at atmospheric pressure.
• Easy to handle in liquid form: The boiling point must be easily controllable so that its ability to absorb heat is also controllable.
• High latent heat of vaporization: The greater the latent heat of vaporization, the greater the heat absorbed per kilogram of refrigerant in circulation.
• Non-flammable, non-explosive, non-toxic.
• Chemically stable: In order to tolerate years of repeated state changes.
• Non-corrosive: To ensure that common materials and the long life of all components can be used in the construction of the system.
• Moderate working pressures: The high condensation pressures – over 30kg/cm2 – require extra heavy equipment. Vacuum operation -less than 0Kg/cm2- introduces the possibility of air penetration into the system.
• Easy detection and location of leaks: Gas leaks and losses lead to refrigerant depletion and contamination of the system and the environment.
• Harmless to lubricating or cooling oils: The action of the coolant in the lubricating oils must not alter the lubricating action.
• Low freezing point: The freezing temperature must be well below any temperature at which the evaporator can operate.
• High critical temperature: A steam that does not condense at a temperature higher than its critical value, no matter how high the pressure. Most refrigerants have critical temperatures above 93°C.
• Moderate specific steam volume: To minimize compressor size.
• Low cost: In order to keep the price of the equipment within reason and ensure adequate service when needed.

How are refrigerant gases classified?

Refrigerant gases are classified in various ways, according to their safety, their flammability and their molecular structure. Let’s look at all their classifications in more detail.

Classification according to their safety (RD 138/2011)

• High security group (L1): In this classification we find the refrigerants R11, R113, R114, R12, R502, R22, R500, R410A, R407C, R424… These refrigerants are characterized by being non-flammable refrigerants with little or no toxic action.
• Medium security group (L2): In this group we can find ammonia, ethyl chloride, methyl chloride and sulphur dioxide. Among its characteristics, it is worth mentioning the possibility of being inflammable, corrosive, toxic or explosive in a percentage in volume equal or superior to 3.5% in air mixture.
• Low security group (L3): These refrigerants are highly flammable and explosive mixed with air at a lower percentage by volume of 3.5%. Because of their low cost they are used where danger is always present and their use does not add another hazard, such as in petrochemical plants and oil refineries. Another of their main characteristics is the need to work at a higher pressure than the atmospheric pressure to avoid increasing the danger of explosion due to the impossibility of air penetration into the circuit. This group may include butane, propane, isobutane, ethane, propylene and methane.

Classification according to flammability (RD 138/2011)

Refrigerants should be included in one of the three groups based on the lower flammability limit at atmospheric pressure and ambient temperature. Their characteristics are as follows:

• Group 1: Non-flammable refrigerants in a vapour state at any concentration in air.
• Group 2: Refrigerants whose lower flammability limit when mixed with air is 3.5% or more by volume (V/V)
• Grupo 3: Refrigerants whose lower flammability limit when mixed with air is less than 3.5% by volume (V/V).

Classification by molecular structure

According to their molecular structure, refrigerant gases are classified into three main groups: CFCs, HCFCs and HFCs.

 

CFC – chlorofluorocarbons – refrigerants

• These are the refrigerants that contain chlorine, fluorine and carbon in their molecule such as R-12 -2 chlorine atoms- and R-11 -3 chlorine atoms-.
• The so-called chlorofluorocarbons were banned from both sale and use on 1 October 2000 by the European Regulation EC No 2037/2000, as they are substances that deplete or destroy the ozone layer – CFC12 and CFC11 -, their ozone depleting potential (ODP) is equal to 1 -CFC11-.

HCFC (hydrochlorofluorocarbons) refrigerants

• These are the refrigerants that contain hydrogen, chlorine – only one atom -, fluorine and carbon as the R-22 refrigerant.
• They were banned on 1 January 2004 for use in the manufacture of both cooling and heat pump equipment and prohibited from use in all cases, including maintenance from 1 January 2015 under European Regulation EC No 2037/2000, as substances that destroy and deplete the ozone layer.

HFC (hydrofluorocarbon) refrigerants

• These are the refrigerants that do not contain chlorine, but contain hydrogen, fluorine and carbon in their molecular structure.
• Their ODS (ozone-depleting substance) is 0.
• In this group of refrigerants, we can find R404A, R407A, R407C, R410A, etc.
• HFCs are “mixed” gases, which means that they are composed of a mixture of several gases or pure substances. These in turn can be separated into two large groups and a sub-group (zeotropic or non-zeotropic mixtures, azeotropic mixtures and quasi-azeotropic mixtures). As we saw in a previous entry, non-azeotropic and quasi-azeotropic mixtures must be loaded in a liquid state.

Why make a gas refill in liquid form? Characteristics of zeotropic and azeotropic mixtures.

Refrigerant evolution

Before the current situation of refrigerants, the banning of CFCs and HCFCs, the families of refrigerants that pure HFCs or mixtures are the current alternative to the long-term replacement of these chlorine-based refrigerants, however other alternatives are being considered such as natural refrigerants like ammonia, linear or cyclic hydrocarbons and their mixtures, CO2 and water (some of these have already been used for a long time in industrial or large capacity installations).