The efficient use of natural resources is an important contribution to the creation of a more sustainable world. Decentralized electricity production through trigeneration systems can save primary energy if these systems operate with a high energy utilization factor (EUF). A high EUF is obtained when the system produces electricity and a substantial amount of the energy rejected by the prime mover is used to meet on-site thermal demands. Energy consumption in buildings varies as the activity, climate and occupancy change at different hours of the day, days of the week, weather conditions and seasons. In this study an annual analysis of an engine trigeneration system is developed as an integrated thermal system (ITS) through a computational simulation program. The ITS simulation uses the characteristics of the system, characteristics of the individual pieces of equipment, design assumptions and parameters, off-design operating conditions, energy demands profiles of the site and climatic data to evaluate the system performance. The obtained results revealed an EUF between 58 and 77% and an exergy efficiency between 35 and 41% for the system. The primary energy savings (PES) analysis showed that the proposed trigeneration system is better than the best available technology used in centralized thermal plants. (C) 2014 Elsevier B.V. All rights reserved.