PhD Thesis - Energy Systems Research Unit - University of Strathclyde

As shown in Figure 1.3 an important component in trigeneration is the thermallyactivated cooling device. There are various types of TAC devices which can be usedin a trigeneration system [23] including absorption chillers [33], adsorption chillers[34], ejector type chillers [35] and rotor based desiccant systems [36]. Given the lowtemperature heat source at which ‘waste heat’ is exhausted from CHP units used inmicro-cogeneration systems (stirling engine-based CHP approx. 90ºC, IC enginebasedCHP approx. 80ºC, proton exchange membrane (PEM) fuel cell approx. 60ºC[23]), single-effect absorption chillers are the preferred type [37].1.3 Assessing the performance of micro-trigeneration in residentialbuildingsAn important aspect in addressing micro-trigeneration development in residentialbuildings is the assessment of the system’s energetic, environmental and economicperformance. Various studies reporting either on the basis of real-life installedsystems or computer generated simulations have already shown the feasibility oftrigeneration systems in excess of 50 kW el . These studies, which includetrigeneration projects in factories [38], hotels [39], educational buildings [40] andsupermarkets [41], have shown that for such projects the fairly constant demand forenergy in these buildings and the associated lengthy utilization times ensureadvantageous rates of return on investment. Micro-trigeneration in residentialbuildings, on the other hand, can be considered quite a novelty with very fewapplications outside laboratories [42].Research into using micro-scale trigeneration in the residential sector has mainlyfocused on the documentation of results obtained from experimental test rig systems[42-44]. Whereas the results obtained from these experimental systems give a clearindication of what the expected micro-trigeneration system performance should befor specific conditions, these studies stop short of indicating how a microtrigenerationsystem would respond to changes in the surrounding environmentalconditions. Overall system performance is largely dictated by the surroundingenvironment and therefore when assessing the performance of a micro-trigeneration9