A simplified model of a polymer electrolyte membrane (PEM) fuel cell has been suggested for simulating packaged commercial fuel cell systems. PEM fuel cell systems are used in building cogeneration applications because of their high efficiency, low transmission loss and pollution, flexible scalability, and low noise. In conventional cogeneration applications, optimization techniques are utilized to size a system and determine proper operational strategies using simulations. To evaluate the performance of a building cogeneration system, a fuel cell model should be concise but accurate to allow its implementation in a whole-building simulation program. Some existing models are appropriate for building applications, but they have some limitations in modeling when a commercial packaged fuel cell system is used. To overcome these problems, a simplified fuel cell model is suggested for commercial packaged fuel cells by adding some new variables and validating through experimental and published data. This model is relatively simple compared to other models but can be easily utilized in some limited cases with performance predictions. (C) 2015 Elsevier B.V. All rights reserved.