Abstract: Apparatus and methods for using said apparatus are described in connection with economized vapor compression heat transfer systems. Working fluid is extracted from a sub-cooler disposed prior to a system evaporator and distributed to the inter-scroll pockets of a compressor via an injection plenum and multiple injection ports for the purpose of increasing ?h across the system to increase its effective heat transfer capacity, thereby providing greater operating efficiency and performance. Further, greater configurability is enabled while manufacturing complexity and cost are reduced.