A refrigeration system includes a compressor for driving a refrigerant along a flow path in at least a first mode of system operation; a first heat exchanger along the flow path downstream of the compressor in the first mode; a second heat exchanger along the flow path upstream of the compressor in the first mode; and a pressure regulator or expansion device in the flow path downstream of the first heat exchanger and upstream of the second heat exchanger in the first mode, wherein the first heat exchanger is positioned within a housing which defines a flow path for heat exchange fluid and the housing defines a zone of reduced flow area along the flow path, and wherein the first heat exchanger is positioned in the zone of reduced flow area.