The function of an oil reservoir, commonly known as an oil trap, is to prevent large oil slugs from forming. This is accomplished by trapping a small amount of oil in the reservoir or trap and gradually returning it to the compressor.
For maximum efficiency, a bank of compressors should be connected to evaporators operating at similar temperatures. From an operational standpoint, cases of different evaporating temperatures can be connected to the rack; however, this causes a substantial energy loss.
If hydrofluorocarbons (HFCs) are to have long-term viability, the low-global warming potential (GWP) versions will have to separate themselves from high-GWP types. And the survivors will have to play their part in energy efficiencies, especially in commercial buildings.