Cap.18: Micro-Organic Rankine Cycle systems for domestic cogeneration

The Chapter presents the requirements and the main features of a domestic cogeneration unit, based on ORC technology. The achievable electrical efficiency and proper sizing are discussed in details, taking also into account other matters of choice, like reliability, safety, noise and the cost of purchasing and operation. For better understanding the possible benefits of a cogeneration system, even with low electrical efficiency, the PES (Primary Energy Saving) diagram and the ERI (Economic Recovery Index) diagram are introduced. Then, the claimed performance parameters of existing models and prototypes are recalled and a comparison is outlined with solutions based on Stirling engines. Afterwards, the main technical features of domestic ORC components are presented, with a special attention for the expander and the feed pump. Also the control strategy options for the unit are presented, taking into account the peculiarity of a domestic application. Finally, two possible options are discussed for the integration of a domestic cogeneration unit: a solar thermal system for drive the ORC and an ejector refrigeration cycles to obtain a CCHP (trigenerative) systems.