Cogeneration System Performance Modeling

A bioDiesel fueled engine generator with heat recovery from the exhaust as steam and from the coolant as hot water has been installed in the Intelligent Workplace, the IW, of Carnegie Mellon’s School of Architecture. The steam and hot water are to be used for cooling, heating, and ventilation air dehumidification in the IW. This cogeneration equipment is a primary component of an energy supply system that will halve the consumption of primary energy required to operate the IW. This component was installed in September 2007, and commissioning is now underway. In parallel, a systems performance model of the engine generator, its heat recovery exchangers, a steam driven absorption chiller, a ventilation unit, fan coil cooling/heating units has been programmed making use of TRNSYS transient simulation software. This model has now been used to estimate the energy recoverable by the system operating in the IW for different characteristic periods, throughout a typical year in Pittsburgh, PA. In the initial stages of this modeling, the engine parameters have been set at its design load, 27 kW, delivering up to 17 kW of steam and 22 kW of hot water according to calculation. The steam is used in the absorption chiller during the summer and in hot water production during the winter. Hot water is used in desiccant regeneration for air dehumidification during the summer, in IW heating during the winter, and in domestic hot water product year around. Systems controls in the TRNSYS simulation direct the steam and hot water produced in the operation of the engine generator system to meet the IW’s hourly loads throughout seasons.