A co-simulation platform and climate-adaptive optimisation for cross-scale PEMFC combined heat and power supply in buildings with semi-empirical surrogate models

Due to the high energy density and clean byproduct water of hydrogen energy, proton exchange membrane fuel cell (PEMFC) combined heat and power (CHP) system has shown promising prospects in low-carbon building transformation. However, comprehensive effects of reactant gas flow on energy loss and output performance in the PEMFC CHP system have not been accurately analyzed. Techno-economic feasibility of the PEMFC CHP system has not been studied for residential building applications in different climates. In this study, with the quantification of energy loss by exhausted gas flow of a PEMFC CHP system, a cross-scale model with cascade levels of cell, stack and system has been developed through a co-simulated multi-software platform of ANSYS Fluent-MATLAB-TRNSYS. Semi-empirical surrogate models are developed to characterize the PEMFC stack performance and interact with balance-of-plant (BOP) component models, so as to enable the co-simulation in both PEMFC stack component and CHP system with synchronized time step. In-field experiments are conducted to verify the model accuracy and energy balance of the H2-to-combined heat and power conversion process. Effects of gas flow on energy loss and power outputs have been investigated throughout the cascade energy conversions. Climate-adaptive operation with flexible heating- and electricity-dominated power outputs is provided by adjustable stoichiometric ratios, together with techno-economic feasibility in extreme weather scenarios. Results show that, the developed cross-scale model is accurate with R-square values of power fittings above 0.969. Due to the dominated heat loss by exhausted gas flow over the increased heat along with the electric power increase, the PEMFC stack thermal power output will decline with stoichiometric ratio rise in low loading conditions. Effect trends of stoichiometric ratios on reacted H2 mass consumption and BOP energy consumption are opposite. Furthermore, under the intercomparison between electricity-dominated output and heating-dominated output strategies, the PEMFC CHP system of electricity-dominated output could save 0.284 kg H2 fuel with slight BOP energy variation of 189.046 kJ daily in Guangzhou (extreme hot climate), while save 21,585 kJ BOP energy and consume extra 0.159 kg H2 fuel in heating-dominated output in Beijing (extreme cold climate). The research can provide a co-simulation technique for cross-scale analysis of the PEMFC CHP system, and give a guidance for control strategy development for climate adaptation and energy efficiency improvement.