The refrigerating circuit is subject to pressure, temperature and expansion phenomena which requires perfect compatibility between oil and refrigerant.
Role of the lubricant in a refrigerating circuit, 3 main functions:
- Lubrication of moving parts,
- Leak tightness,
- Motor fluid for some control and cooling devices in the case of screw compressors for example.
Though the lubricant is essential for the compressor to reduce friction, wear and improve the seal during compression, conversely, oil in the refrigerating circuit must be kept to a minimum to prevent heat transfer loss.
- Lubricity: related to the thickness of the oil film.
- Solubility with the refrigerant in the gaseous state.
- Miscibility with the refrigerant in the liquid state.
- Viscosity: resistance to temperature variations.
- Flocculation point: important, particularly in the context of installation conversion.
E.g. in an installation converted with R-134a + POE ISO 22, the flocculation temperature of POE will increase from -53°C without residual mineral oil to +16°C with 5% residual mineral oil.
Oil has many other properties such as pour point, stiffness, dielectric, moisture content, chemical stability, thermal stability, hydrolysis resistance and acid value.
Installation conversion: oil as a flush solution
When converting an installation in good condition to hydrofluorocarbons , POE oil can be used as a flush solution for the oils in service. Climalife, on the strength of its many experiments with this type of operation, recommends using POE oils with an appropriate viscosity grade for machines to remove mineral oils or alkylbenzenes from circuits by successive draining and operating with HCFC, as well as the in-service compressor.
The compatibility of all system components should be checked beforehand and will be combined with a number of implementation measures and precautions. When the residual minimum has been reached (checked by DPH analysis), after recovering the HCFC fluid and changing all incompatible components, the HFC replacement fluid can be loaded with a new POE oil.
The installation will then be restarted and optimised by the appropriate settings. When the use of a solvent is not necessary, this solution is much easier and faster to implement.
Checking the state of the oil:
The oil plays a key role in the proper operation and useful life of the installation. There are several ways to check its in-service state
Acidity test: Climalife offers Acitest Unipro in a single bottle to instantly check the acidity of the in-service oil on site (regardless of its type MN/AB/POE, etc.).
DPH analyses: for larger installations or those with a maintenance contract.
The DPH, performed in the laboratory, determines the health of your oil and therefore your installation with as much precision as a medical analysis. The oil's values are compared to standard values and recommendations are made by our experts.
Article written by Pierre-Emmanuel Danet
Climalife Technical Support Manager