Abstract: A single or multiple evaporator vapor-compression refrigerant system for single or multi-story structures includes a lubricating oil collection reservoir and a separate oil pumping unit for returning oil separated from the refrigerant fluid in the refrigerant flow circuit to the compressor unit. In multi-story, direct expansion, vapor-compression, air conditioning systems, a simplified generally vertical refrigerant vapor return riser is provided with an oil reservoir at the lowest elevation point of the riser and a liquid level sensing switch for energizing and deenergizing the separate lubricating oil pumping unit. The pumping unit may include an electric or refrigerant fluid driven motor connected to a pump or the pumping unit may include a pressure vessel into which high pressure refrigerant vapor is admitted to displace oil back to the compressor through an oil return conduit.

Abstract: A single or multiple evaporator vapor-compression refrigerant system for single or multi-story structures includes a lubricating oil collection reservoir and a separate oil pumping unit for returning oil separated from the refrigerant fluid in the refrigerant flow circuit to the compressor unit. In multi-story, direct expansion, vapor-compression, air conditioning systems, a simplified generally vertical refrigerant vapor return riser is provided with an oil reservoir at the lowest elevation point of the riser and a liquid level sensing switch for energizing and deenergizing the separate lubricating oil pumping unit. The pumping unit may include an electric or refrigerant fluid driven motor connected to a pump or the pumping unit may include a pressure vessel into which high pressure refrigerant vapor is admitted to displace oil back to the compressor through an oil return conduit.