A Novel Solid Oxide Fuel Cell Tri-Generation System for Low Carbon Buildings

As a result of growing concerns of climate change and ever increasing cost and scarcity of fuel resources, fuel cells with their high electrical efficiency, low emissions and useful heat output have been identified as a key technological option for improving both building energy efficiency and reducing emissions. A 1.5kWe low temperature solid oxide fuel cell (SOFC) liquid desiccant trigeneration system has been proposed as an environmentally friendly way of providing heating, cooling and electricity to low carbon buildings. The described system will be constructed and trialled at The University of Nottingham as part of a European Union (EU) funded project named Durable Solid Oxide Fuel Cell Tri-generation System for Low Carbon Buildings (TriSOFC). The aim of this paper is to provide an introduction to the EU TriSOFC project. The paper is split into three parts. The first part, section two, provides details of the TriSOFC system along with project aims and objectives. The second part, section three, presents a review of the state-of-the art surrounding fuel cell and desiccant based tri-generation systems. Conclusions of the review are discussed in terms of their impact on the TriSOFC system, most significantly (1) a considerable gap in the literature currently exists surrounding tri-generation energy systems based on SOFC combined with liquid desiccant air conditioning technology and fuel cell based tri-generation systems in residential applications (2) the thermal output of a fuel cell combined heat and power (CHP) system is in good thermal agreement with desiccant regeneration temperatures, making them appropriate companion technologies for integration in a tri-generation system concept, and (3) maximising thermal energy utilisation in CHP and tri-generation systems is challenging, and can have a large impact on system efficiency. The third part of the paper, section four, presents the parametric modelling results for a liquid desiccant air conditioner. Parametric studies have investigated the influence that, cooling and heating water temperature, fluid flow rates, inlet air conditions and desiccant solutions (LiCl, CaCl2 and CHKO2), have on performance. There are four conclusions from the modelling work. First, the moisture removal rate of the supply air is strongly controlled - assuming constant mass flow rate, by desiccant temperature and cooling water temperature. Second, the air inlet conditions have a large influence on performance in terms of cooling output. The unit will generally perform better in a hot and more humid climate such as southern China, as opposed to drier cooler climates such as the UK. Third, as the regeneration heat source temperature increases, the mass of water vapour vaporised from the weak desiccant solution increases. Fourth, in this model the CHKO2 desiccant solution shows the highest performance for the given conditions, and with its low environmental impact, is a suitable solution for the desiccant unit in the TriSOFC system. A separate paper presented at this conference (Paper ID: 334) reports the development of computer simulations carried out to evaluate the novel desiccant membrane contactor design that will be used in TriSOFC and size the desiccant system.