ENERGY AND EXERGY-BASED MODELING AND EVALUATION OF A MICRO-COMBINED HEAT AND POWER UNIT FOR RESIDENTIAL APPLICATIONS

Micro-Combined Heat and Power (MCHP) systems, for distributed residential power generation applications are interesting alternatives to conventional systems based on separate production. A simplified approach for the analysis of these systems is typically based on the evaluation of energy flows, concerned with quantity aspects only and neglecting important features related with quality. For this reason, the energy assessment of these systems can be improved by means of exergy methods, that quantify the quality or “work potential” of the energy flows, aiming to assess and compare processes and systems more rationally and meaningfully. Based on laboratory experiments, the energy performance of an MCHP unit was assessed from 1 to 6 kW (electric). Afterwards, a calibrated simple model of the unit was implemented in TRNSYS, where the exergy method was included. The model can assess energy and exergy performance indexes related to the MCHP system and evaluate different supply scenarios, including integration of renewables. Regarding to compare the MCHP unit with a given reference system (separate heat and power “production”), the indicators Primary Energy Savings (PES) and Relative Avoidable Irreversibilities (RAI) are applied and discussed. The results indicate that RAI gives a better indication about the “true” value of the savings between systems and it is a complementary indicator to PES since it is able to find more efficient supply options, when different type of renewables are compared.