The presence of oil in domestic heat pumps is a hindrance, particularly for enhanced surface evaporators and for advanced concepts based on two-stage cycles. Very compact oil-free dynamic compressor directly driven by high speed electric motors and supported on refrigerant vapor bearings represent a promising alternative. This paper presents a design analysis of the first stage prototype with the various tradeoffs between the impeller characteristics to follow the seasonable heat demand, the bearing and rotor stability and the constraints linked with the high speed electric motor. Refrigerant chosen for the first experimental approach is HFC 134a with a 20 mm diameter impeller, a 6 kW motor and self-acting bearings. The impeller design and predicted performance as well as the experimental facility for the initial tests are presented.