Benefits of knowledge about refrigerant quality in the refrigeration circuit

The quality standards set for virgin refrigerants, as well as those that have undergone the reclamation process, are discussed in the AHRI 700 standard. It defines both the maximum content of contaminants in refrigerants and the methodology for their testing.

Knowledge gained from the analysis results allows the detection of the source of installation malfunctions. Confirmation of high refrigerant quality contributes to more efficient cooling and longer equipment lifespan. By knowing the parameters of the refrigerant from the system, the service technician can help reduce the energy consumption of the equipment, as well as raise the level of operational safety of the installation.

Exceeding individual refrigerant parameters can have a significant impact on the operation of the entire installation:

• composition analysis using gas chromatography

– performed in order to exclude elevated impurity content and to confirm the appropriate percentage composition of individual refrigerant components. The permissible impurity content is 0.5% by weight. An elevated amount of impurities and an inappropriate percentage composition of the refrigerant result in higher energy consumption and inefficient operation of the installation. A change in composition may also have consequences in the deterioration of refrigerant flow conditions inside heat exchangers due to an increase in liquid viscosity. Furthermore, a change in composition affects the temperature glide, causing it to change, and consequently leading to changes in the regulation of expansion valves.

Figure 1. Gas chromatograph used for testing the composition and content of non-condensable gases

moisture testing using the Karl Fischer method

– the permissible amount of moisture in the refrigerant according to the standard is 10 ppm. Excessively high water content in the refrigerant can cause blockage of the throttle valve, which is a component of the refrigeration system, which in turn leads to a reduced cooling capacity of the installation, meaning the refrigeration system ceases to fulfil its function. Furthermore, an increase in moisture content can lead to equipment lockout, as well as compressor and condenser failure.

Figure 2. Karl Fischer coulometer is a specialized device used for measuring moisture content

• acidity testing using alkalimetric titration method

– the permissible acid content in the refrigerant is 1 ppm expressed as hydrochloric acid (HCl). Elevated acid content may result in damage to installation components.

• testing of solid and high-boiling residue content

– high-boiling residues – oils; solid residues – metals and other contaminants. The presence of solid and high-boiling residues is permitted at a level of 0.01% by volume. The proper operation of the refrigeration installation is ensured, among other things, by an appropriate amount of refrigerant (adapted to the size of the installation), and an excessively high oil content in the circuit prevents cooling at the required level.

• testing for the presence of chlorides

– a refrigerant with correct parameters should not contain chlorides, which is why we test not for the content of chlorides, but for their presence.

• testing of non-condensable gas content

– the standard specifies the non-condensable gas content at a level of 1.5% by volume. An increase in this parameter can lead to a rise in pressure within the installation, resulting in valve misalignment. Furthermore, it may also lead to increased compressor operating pressures and its accelerated wear.

Properties of compressor oils

In addition to knowledge of refrigerant parameters, the aspect of compressor oil properties is also important, as they also play a significant role in the refrigeration circuit.

Just as with the knowledge provided from refrigerant analysis results, the technical condition of the oil allows for the detection of the source of malfunctions in the installation’s operation.

• water content testing

– the permissible value depends on the intended use of the oil; in the case of oils for refrigeration compressors it is 100 ppm. The presence of water in quantities greater than permissible may indicate water infiltration into the oil system from other circuits, such as the water cooling system. Exceeding the permissible moisture value causes oil degradation – decomposition of the oil through hydrolysis in the case of polyester oils, decomposition of performance-enhancing additives, causes seizure and accelerated wear of friction components, as well as metal corrosion, and in some cases may promote the growth of microorganisms.

• kinematic viscosity testing

– during oil use, depending on its chemical composition and the influences acting upon it (thermal, chemical, mechanical), viscosity may either decrease or increase. Increased oil viscosity indicates progressive oxidation processes resulting from elevated temperatures, or is the result of topping up with oil of higher viscosity than that already present in the system. Decreased viscosity is most commonly the result of introducing a solvent into the oil, adding oil of lower viscosity, or shearing of a polymeric additive.

• acid number testing

– the maximum permissible acid number for compressor oil is 0.1 mgKOH/g. Oil acidification is the result of oxidation of its less resistant components; furthermore, some oils contain additives of an acidic nature, the decomposition of which leads to a decrease in the acid number, which is why the acid number value should neither increase nor decrease.

• elemental content testing

– P, B, Zn, Mg, Ca 

– these are components of additives that improve oil properties. Their content generally decreases during operation, due to oxidation processes, thermal decomposition, and sometimes also the effects of water.

– Fe, Cu, Al, Pb, Cr, Sn 

– an increased content of these metals catalyzes the oxidation and thermal decomposition processes of oil components. A gradual increase in the amount of these metals in the oil indicates a progressive wear process of metal friction surfaces.

– Fe, Cu 

– an elevated content may also indicate the occurrence of corrosion and rusting processes;

– Cu, Sn 

– if the content increases, this indicates wear of parts made of tin bronze (bushings, bearings);

– Cu, Pb

– if the content increases, this indicates wear of parts made of lead bronze (bearings, plain bearings);

– Al

– if the content increases, this indicates wear of parts made of duralumin;

– Si 

– the presence of silicon in the oil is most commonly caused by external contaminants in the form of silica (dust, sand) entering the oil system.

Marta Wiśniewska 

Laboratory Manager