The purpose of oil in a refrigeration system is to lubricate the compressor that produces cold air. Oil reduces friction on metal parts, reducing wear on the compressor and prolongs the life of the system.
Refrigerant oil is a special high-temperature formulation designed for use in cooling systems, so it is important to use the recommended lubricant for the equipment. Oil that is too heavy will not flow smoothly to all working parts. Oil that is too light will not adhere properly, causing inadequate lubrication.
How the oil lubricates the system
The process of circulating refrigerant gas to cool a freezer, chiller or home refrigerator creates an increase in gas pressure and temperature. As the temperature rises, metal parts begin to heat up. This causes an increase in vapor pressure of the refrigerant oil, which advances through the system to lubricate the hot metal parts of the compressor. Cooling and lubricating the hot metal allows the compressor to operate efficiently while reducing wear and tear on the components.
The type of oil needed to lubricate a specific type of refrigeration equipment depends largely on compressor capacity, which is a measure of the system's ability to cool. This is measured in BTUs, or British Thermal Units.
Types of oils used in refrigeration systems.
Refrigeration systems depend on two main types of lubricant: synthetic and mineral oil.
While synthetic oil is longer lasting, mineral oil costs half as much and is typically used in industrial applications, such as air conditioning units for commercial buildings and grocery-store freezers.
The exact formulation of oil for a specific compressor depends on the size and power requirements of the compressor. Oil viscosity, which measures the resistance of the lubricant to various factors such as heat and pressure, is the main factor in determining the formulation of lubricant to be used in a compressor.