A simulation framework for flexible evaluation of various distributed building energy systems based on the integration of component device simulation models is presented. Device technology models were constructed for a solid oxide fuel cell (SOFC), a gas turbine, a double pipe heat exchanger, and a compressor. A scheme is proposed for defining model interfaces in order to improve the flexibility and accessibility of the models. Based on that scheme, interfaces are defined for each device model. The component device models are integrated to construct system models of (1) a hybrid system combining an SOFC and a gas turbine (SOFC/GT system) and (2) a stand-alone SOFC system. The integrated model of the SOFC/GT system is then used to carry out a multi-objective optimization in order to study the tradeoffs between cost and CO2 emissions of the SOFC system operation for a given electricity demand. Through these analyses, the optimal configuration of the SOFC/GT system and the optimal operation conditions of the SOFC system for the given electricity demand were explored. Copyright (c) 2005 John Wiley & Sons, Ltd.