Trigeneration systems assisted by solar energy: design criteria and off design simulations

The present work focuses on CHCP systems, made up of gas engine as prime mover and absorption chiller as cooling device, combined with Evacuated Tube solar thermal Collectors (ETC). Such an energy system has provided the EURAC building with heating and cooling since 2002 and has been monitored since 2005. Thanks to the monitoring data, critical aspects have been highlighted concerning the size selection of some components, the overall layout and control strategy (Chapter 1). On the basis of this outcome, a procedure for optimal designing CHCP plus ETC systems has been defined and includes: 1. the layout and the control strategy selection (Chapter 2): beside the already mentioned basic components, the layout also includes a biomass boiler, as a further renewable heat source, and a compression chiller, as a cooling back up device; 2. the definition of a sizing procedure for each component of the layout (Chapter 3): this procedure is based on a spreadsheet which requires the heating and cooling demand of the building and a first sizes selection concerning the absorption chiller, the cogenerator and the solar collectors in order to output the sizes of all the left plant components; 3. the development of a TRNSYS deck which simulates the designed plant at off design conditions (Chapter 5): to this end, two new models have been developed in MATLAB respectively for a gas engine based cogeneration unit and a biomass boiler (Chapter 4). Such design procedure has been applied in order to select the sizes suitable to match the EURAC heating and cooling demand. On this subject, by repeating the sizing procedure with different initial sizes of the major plants component and by considering different control strategies, various configurations have been output. Such configurations have been simulated in TRNSYS to calculate the Primary Energy Consumptions (PEC), the Operation Costs (OC) and the CO2 emissions which can be saved by the examined system with respect to a conventional system. By comparing the savings turned out of all the simulations, the optimal size of the cogeneration unit, the biomass boiler, the absorption and the compression chiller have been identified. The obtained results have also been discussed from the point of view of the Discounted Pay Back Period (Chapter 6).