A Micro-ORC Energy System: Preliminary Performance and Test Bench Development

A large market potential for small electricity and heat generators can be identified in the domestic sector. Among the under development micro-scale power generation technologies the ORC (Organic Rankine Cycle) concept is a promising solution, already proven in the MW-range of power. There is still a prospective for smaller units for domestic users, with low temperature thermal demand. A test bench for a micro-CHP unit, currently run with a prototypal prime mover, is under development at University of Bologna. In particular, the system in study in the test facility is a micro-ORC system, rated for up to 3 kW. The ORC input heat is provided from an external source, which can be an external combustion system (a 46 kW biomass boiler will be connected to the thermal cycle) or an electric heater. The heat source delivers hot water to the bottoming ORC, currently operated with R134a as working fluid, which evolves in a recuperated cycle, with a 3-piston reciprocating expander, producing mechanical/electric power. The residual low-value heat is discharged to the environment with a water cooled condenser. The hot and cold water circuits have been realized in the lab to test the ORC performance. The micro-ORC internal layout and the external hot and cold water lines have been instrumented, implementing an acquisition and control software by means of LabVIEW software. A preliminary test campaign has been performed on the micro-ORC system, obtaining information on the actual thermodynamic cycle and the real performance under different operating conditions.