Transcritical vapor compression cycle device with a variable high side volume element.

An apparatus and a method is provided for varying high side pressure in a transcritical vapor compression cycle by means of variable volume element(s) connected to the flow circuit. The apparatus comprises a variable volume element (5) having a compartment connected to and communicating with the high side to permit entry of refrigerant into the compartment, and a movable partition means defining at least one side of the compartment and being displaceable between first and second positions respectively defining first and second volumes of refrigerant within the compartment.