After carrying out a study on the effects of mixing of refrigerant gases, and supporting the importance of carrying out a retro-fit correctly, we wish to explain what happens if gases are mixed in a refrigeration circuit, as well as the behaviour of and effects on the system in the event of gas leakage.
Firstly, we will give a brief explanation/classification of the refrigerant gases.
With regards to their chemical composition, refrigerant gases are classified into:
NATURAL (non halogenated)
These are gases with a very low global warming potential (GWP). Their use has no effect on the ozone layer, and their influence on environmental conditions is minimal. Within the group of natural refrigerants, we have:
• Ammonia (NH3 – R717) – inorganic
• Hydrocarbons (HCs): propane (R290), butane / isobutane (R600 / R600a), and their derivatives
• Carbon Dioxide (CO2 – R744) – inorganic
• Water (R718) – inorganic
According to their composition, this group can be divided into:
• HFO / CFC – fully halogenated halocarbons without the presence of hydrogen. They are composed of chlorine, fluorine and carbon. For example, R-12 and R-11, which has already been phased out.
• HCFC – partially halogenated halocarbons with the presence of hydrogen, chlorine, fluorine and carbon. This group includes the pure HCFCs such as R-22, and mixtures (derivatives of R-22).
• HFC – partially halogenated halocarbons with the presence of hydrogen, fluorine and carbon, and absence of chlorine. This group includes the pure HFCs such as R-134, and mixtures (R-4XX and R-5XX).
Within the category of gases resulting from a mixture, and with regards to their behaviour during the change of phase, we obtain the following sub-classification:
– Azeotropic mixtures of refrigerant gases:
• These are refrigerant gases composed of a binary substance which nevertheless behaves as a pure gas, with a constant boiling point, and which maintains its composition at a constant pressure in both liquid and gas phase. When it starts to boil, the two gases evaporate in the same proportions, and when they return to their liquid state (condense), they will do so in the same proportions; it is not possible to separate them by simple distillation.
• The fact that they always maintain their proportionality means that additional loads of refrigerant gas can be applied without unbalancing the refrigeration system.
• Not all liquids form azeotropic mixtures, since their density, boiling point and surface tension are different.
• The boiling points of azeotropic gases have minimum slippage (practically none). Examples of these gases are R-507, and R-502.
– Zeotropic mixtures of refrigerant gases:
• These are refrigerant gases which do not present the same proportions on evaporation or condensation at a constant pressure.
• During the process of change of phase, the components may segregate or separate due to different evaporation/condensation temperatures. However, by the end of the change of phase, the gas is once again the same. This difference in temperatures is called slippage.
• An example of a zeotropic gas is R-404A, even though its slippage is minimal.
• An added problem of zeotropic gases is that in the event of a leak, the gas is not lost in equal proportions, meaning that it will not respect the initial concentrations of the refrigerant gases inserted at time of installation.
Gas mixtures and their effects:
– The first effect concerns the composition; when refrigerant gases are mixed, they form new zeotropic compositions with uncontrollable slippage, which may result in backflow of liquid to the compressor, causing considerable damage to it (the compressors are designed to compress gas, not liquid).
– Another disadvantage is the miscibility of each gas with the lubricant. The absence of lubricant radically affects the operation of the mechanical parts.
– Refrigeration circuits, in their expansion phase, serve as capillary valves designed and calculated for each specific refrigerant gas. Therefore, a mixture of gases shows unstable behaviour in the circuit.
In the event of a leak:
The main problem in the event of a leak is the entry of humidity into the refrigeration circuit interior. Humidity inside the refrigeration circuits causes a reaction between the oil and the refrigerant agent, generation acid.
These acids in turn generate metal salts and oxides (of iron and copper) which obstruct the oil filters, and copper particles appear on metal parts, giving rise to:
• The progressive deterioration of mechanical parts due to lack of lubrication.
• Degradation of the motor winding insulation, causing short circuits.
We hope that this brief explanation has helped you understand the considerable damage that both mixing refrigerant gases and leaks cause to the performance of refrigeration systems and to the useful life of their components. We therefore discourages this practice.
When we recover a refrigerant gas from a refrigeration facility and given the condition in which this gas finds itself, it is sent to a waste management company for destruction. We never reuses this gas.
We only uses refrigerant gas from factory and/or approved suppliers.