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Tri-generation System Analysis

In this section, the validated SOFC CHP and liquid desiccant air conditioning sub-component models are combined to form a complete SOFC liquid desiccant tri-generation system model. Figure 4.1 presents a schematic of the novel system. The SOFC CHP system generates heat and power simultaneously. In CHP mode the heat is used directly in heating applications. In tri-generation mode, the heat is used to regenerate the desiccant solution so that the desiccant air conditioning system can operate continuously and dehumidified cool air can be produced. The performance of the tri-generation system will be assessed based on its tri-generation efficiency, as defined in Eq. 4.32.

The tri-generation system efficiency is defined as the ratio of the overall tri-generation system energy conversion (electricity + heating + cooling) over the total amount of energy input to the system. The net electrical output is defined as the total AC electrical output from the SOFC less the electrical requirement to operate the liquid desiccant systems pumps and fans, and has been assumed constant, from empirical data, at 110 W. The net heat output is defined as the total thermal output from the SOFC CHP unit less the thermal energy input required to regenerate the liquid desiccant solution. The energy input to the tri-generation system is the required fuel energy input {Qch_4 to the SOFC CHP unit.

The results from the tri-generation system analysis are presented in three sections. First, Sect. 4.3.1 presents a specific case based on the thesis technical objectives. The specific case will provide a theoretical benchmark value for the first of its kind SOFC liquid desiccant tri-generation system. Following this, Sect. 4.3.2 provides a parametric analysis to investigate the effect changes in electrical and cooling capacities have on the overall tri-generation system performance. The aim of this is to understand the interaction between sub component operation and overall tri-generation system performance. A 24 h tri-generation simulation is also provided. Finally, Sect. 4.3.3 presents a tri-generation system climatic performance investigation. The aim of this is to evaluate the performance of the novel system under ‘real’ operating conditions to see how it performs in different geographical locations. Throughout the analysis, the SOFC tri-generation system performance is compared to a conventional separated system comprising grid electricity, gas fired boiler and vapour compression cooling system.

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