Analysis and optimization of fuel cell cogeneration systems for application in single-family houses

Abstract

The world’s demand of energy is projected to double by 2050 in accordance with population growth and with the industrialization of developing countries. The supply of fossil fuel could be limited and even worse is concentrated in a few regions of world, while demand is growing everywhere. One promising alternative to fossil fuel is hydrogen which is abundant and generously distributed through the world without regard for national boundaries. The aim of this paper is to explore this early market opportunity for fuel cell cogeneration systems in buildings and to determine the conditions under which they might compete with the alternative of purchased power. It is suitable to identify and to provide solutions for problems encountered in adapting these systems to buildings through a process which involve three steps: - Determination of buildings energy annual demand compiled by a data acquisition system or logged daily by operators - Characterization of a specific fuel cell in terms of amount of heat flow available and its temperature level, based on the power output of the system - Calculation of annual energy costs (natural gas fuel and possibly purchased electrical energy) for providing power, heat and air conditioning and comparison with operating costs of existing buildings. The energy cost savings provided by the various cogeneration systems were used to provide estimates of what capital costs for each of these systems might be economically justified A numerical model is developed to perform a fuel cell cogeneration system, coupled with a Thermal Energy Storage (TES), in accordance with energy requirements of a single-family residence. The objective of the mathematical model is to calculate the energy allocation for each system component and to determine fuel use of the system on hour basis. The operation of the cogeneration system is dependent on the temperature of TES (TTS ) which varies during the hours. If the tank is hot enough (TTS ≥ Thwx temperature limit for electric domestic water heating) it can supply the entire domestic water load, otherwise if the tank is too hot (TTS ≥ Tfcx temperature limit for external heat rejection from the fuel cell) the heat transfer from the fuel cell will be limited. Two conventional systems connected to public grid are investigated as alternatives to the cogeneration ones.