Modeling and Integration of a Combined Cooling, Heating and Power System with a High Temperature Fuel Cell and Absorption Chiller.

摘要

Combined Cooling, Heating and Power (CCHP) presents an opportunity in commercial buildings to reduce electrical loads while increasing efficiency and emissions. In particular, High Temperature Fuel Cells (HTFCs) coupled with Absorption Chillers represent an opportunity to provide electricity, heating, and cooling to buildings at very high efficiencies. Because this combination has been demonstrated on only a few occasions, a need is evident for detailed system modeling and optimization to assure that the technology can meet its full potential and serve a wide variety of applications.;In this thesis, the installation of a HTFC-Absorption Chiller system is analyzed and modeled in order to determine a favorable strategy for installation into an existing but generic commercial office building. Building loads were monitored and analyzed to establish the building electrical and HVAC demand. For the purposes of this system analysis, the HTFC is assumed to operate at steady state at all times. A steady state absorption chiller model was created in Aspen PlusRTM in order to analyze different operating points, given varied fuel cell exhaust conditions. Next, a dynamic absorption chiller model was created in Matlab SimulinkRTM. This thermodynamic model incorporated mixing volumes, thermal mass, and transport delay in order to capture transient effects in the absorption chiller.;The Aspen PlusRTM and SimulinkRTM absorption chiller models were verified against manufacturer provided steady state data. Since the exhaust leaving the fuel cell during normal operating conditions was too high, analyses were performed with the steady state model to determine the best methods of reducing the temperature of the fuel cell exhaust. In parallel, simulations were run with the transient model to determine the ability of the absorption chiller to follow dynamic cooling loads throughout the day. Finally, representative load days were simulated while imposing operational constraints on the dynamic absorption chiller model. The use of a thermal energy storage (TES) tank was also analyzed. The most simple temperature reduction method, which alters the fuel cell steam-to-carbon ratio, is favored, combined with methods of diverting unnecessary exhaust from the chiller and sending it to a heat recovery unit. A heating-only mode, with the chiller configured for heat recovery, is the most effective method for energy utilization during the winter, when the cooling demand is marginal.