Prototype of a thermally driven heat pump based on integrated organic Rankine cycles (ORC)

The concept studied in this work is a low power ORC-ORC system (about 20 kW heat at the condenser) which is composed of an ORC engine cycle driving a reversed ORC heat pump cycle, both using the same fluid. The radial compressor and turbine are directly coupled on the same shaft rotating on refrigerant gas bearings. This gives the system the advantage of being oil-free, fully hermetic and with low maintenance costs. The paper presents the development of an ORC-ORC prototype, with HFC-134a as working fluid. The main critical parts of the system are the compressor-turbine unit, the supercritical evaporator and the pump. The selected type of heat exchanger for the supercritical evaporation is the double tube coil (DTC). A first experimental setup has been built to test the pump and the supercritical evaporator. A comparison has been done between the results obtained with an in-house supercritical evaporator simulation tool and the measurements made on the DTC. The design steps of the compressor-turbine are briefly presented. The compressor-turbine unit has been balanced and tested, with air, at speeds up to 140'000 rpm.