Already existing man-made infrastructures that create water flow and unused pressure are interesting energy sources to which micro-hydropower plants can be applied. Apart from water supply systems (WSSs), which are widely described in the literature, significant hydropower potential can also be found in district heating systems (DHSs). In this paper, a prototype, a so-called energy-recovery pressure-reducer (ERPR), utilized for a DHS, is presented. It consisted of a pump as a turbine coupled to a permanent magnet synchronous generator (PMSG). The latter was connected to the power grid through the power electronic unit (PEU). The variable-speed operation allowed one to modify the turbine characteristics to match the substation’s hydraulic conditions. The proposed ERPR device could be installed in series to the existing classic pressure reducing valve (PRV) as an independent device that reduces costs and simplifies system installation. The test results of the prototype system located in a substation of Cracow’s DHS are presented. The steady-state curves and regulation characteristics show the prototype’s operating range and efficiency. In this study, the pressure-reducer impact on the electrical and hydraulic systems, and on the environment, were analyzed. The operation tests during the annual heating season revealed an average system’s efficiency of 49%.
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