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A pair of mechanically driven small-scale turbocompressors running on gas lubricated bearings have been designed for a two-stage heat pump application functioning under variable operating conditions. Novelty in the present two-stage heat pump system lies in the application of oil-free turbocompressor technology and the introduction of unused sec-ondary heat from various sources. Managing the operational deviations and the secondary heat during off-design heat pump operation is challenging for the turbocompressors. The turbocompressors can potentially exceed their operating range defined by the surge and choke margins, and the maximum rotational speed limit set by the structural and rotor-dynamic considerations. A wide operating range is, therefore, a prerequisite design condition for the turbocompressors. The present paper will guide the readers through different stages of the design process of such turbocompressors sub-jected to various operational and design constraints. Moreover, a stochastic evaluation on the influence of variable operating conditions on the heat pump off-design performance will be detailed.