PhD Thesis - Energy Systems Research Unit - University of Strathclyde

trigeneration system primary energy consumption. In the latter case, given that partof the thermal load satisfied by the micro-trigeneration system was required to coverfor storage heat gains which were not accounted for as a useful energy product,Scenario 3 High (although being the plant configuration with the highest number ofoperating hours) was the scenario with the lowest efficiency.Two clarifications on the system efficiency which need to be mentioned are that:The system efficiency values reported in Table 5.10 for the differentscenarios are the overall system efficiency and not the individual fuelefficiency values of the CHP unit (approximately 27% electrical efficiency,65% thermal efficiency and 92% total fuel efficiency - reported in the CHPunit specs sheet [3]). As explained in Chapter 4 the system efficiencyinvolves the calculation of all the energy products produced by the microtrigenerationsystem divided by the total energy input and therefore includesthe various inefficiencies of the different components (e.g. the CHP unit, theabsorption chiller, storage heat losses etc.). In this context the calculatedvalues for the system efficiency reported for the different scenarios showconsiderable agreement with the system efficiency values reported by Lin etal. in [4] and Khatri et al. in [5], who conducted experimental laboratoryinvestigations on residential micro-trigeneration using a relatively similarplant setup; andAlthough the equation for system efficiency, (equation [4.10]) explicitlydistinguishes between the net electrical demand satisfied by the microtrigenerationsystem and the net exported electricity, the results for thedifferent scenarios shown in Table 5.10 are not differentiated on the basis oftheir electrical efficiency. Since the gross electricity cogenerated by thesystem (which is equal to the aggregated contribution of the net export andthe net demand satisfied by the system) is independent of the electricaldemand (the effect on internal heat gains due to a change in electrical demandis negligible) and dependent only on the thermal demand, it follows that the192