REGEN-BY-2 is a Horizon 2020 EU-funded project, that aims to develop a first-of-its-kind lab-scale prototype of a highly efficient thermodynamic cycle and related plant for the valorisation of renewable thermal energy sources, unlocking their large potential to supply electric, heating and-or cooling energy vectors. The investigated thermodynamic cycle, which will be described in the paper, is highly efficient as it is constituted by a proper combination of Carnot cycles operating with a two-phase fluid circulating in novel two-phase expanders and two-phase compressors. The aim of this paper is to present numerical investigations performed to characterize the performance of two two-phase scroll compressors being part of the plant. In this article, a compressor deterministic model is discussed, and simulations results of an off-the shelf scroll compressor are commented. No inlet tube pressure drops and no heat transfer are assumed while leakages and mechanical losses are considered in the model. For on-design operating condition (vapor quality of 39% at the compressor inlet with the HFO R1233zd(E) as a working fluid), the simulation results show a reduction of the leakages due to a sealing effect leading to volumetric efficiencies close to 100% under the given assumptions. On the contrary, isentropic efficiencies below 70% are obtained for high pressures ratios, under-compression losses being emphasized when working with two-phase flows due to high pressure drops across the discharge port.