How changes in lubricant can address challenges associated with hydrocarbon refrigerant High Temperature Heat Pumps (HTHP)

DOI: 10.18462/iir.compr.2024.0628

Sekcia: Heat pumps I

Stav prijatia: Abstrakt prijatý

Autori

Abstrakt

The heart of an HP is a compressor with lubricant for its moving parts. For positive displacement compressors lubricant also plays a role in the isolation of high- and low-pressure sides of the circuit. The lubricant selected must provide enough viscosity in the operational conditions to fulfill these two roles, otherwise the compressor will have a premature failure.
The knowledge of lubricant-refrigerant interactions is crucial to understand the behavior of a real working system.
One of the most important points to look at is rate of dilution experienced by the lubricant in the HP system once refrigerant dissolves in the oil. The greater the affinity between refrigerant and lubricant, the greater the temperature, or the greater the pressure, all of them reduce the working viscosity available during operation. An increase in the viscosity grade may compensate, but there are also operational high viscosity limits. The greater the difference between nominal and working viscosity, the greater start up time.
A different lubricant chemistry can compensate the high solvent capability of the hydrocarbon refrigerants. The opposite extreme is total immiscibility, but the system has to be purposely designed for. The use of a miscibility chart will be explained with real examples.
The behavior of lubricant-refrigerant pairs will be described in two scenarios: the oil sump in an alternative compressor, and the oil reservoir in a screw compressor. How different operational conditions influence differences in oil behavior and in oil selection, to provide the right viscosity at the right condition. All explanations will be illustrated with real products and working conditions.

Kľúčové slová

Heat Pump
Lubricant
Hydrocarbon Refrigerants
Extreme conditons