PhD Thesis - Energy Systems Research Unit - University of Strathclyde

The PES obtained for the different scenarios are all within a small range suggestingthat the overall impact of the different operating conditions on the PES is low. Fromthe results, certain trends can nonetheless be deduced: If the net imports are not included in the calculation and the effect of the changein electrical demand on the internal heat gains is negligible (as it is in this case),the thermal performance, the cogenerated electricity and hence the PES is thesame for both appliances’ electrical efficiency; At the current level of grid efficiency, including the net imports in thecalculation significantly reduces the PES. Since in the appliances’ high electricalefficiency case less net imports are required the highest PES is obtained forscenarios modelled using this level of electrical efficiency; Increasing the useful thermal load (e.g. when connecting the plant system to alarger building etc.) results in longer operating hours and hence in a higher PES; Improving the building fabric has a marginal negative effect on the system’sPES. This negative effect is however compounded if the net electrical importsare included in the calculation of the PES; The addition of systems making use of renewable energy to offset part of thefuel consumption increases the system’s PES. The plant system including theSWH (Scenario 4) is the plant configuration with the highest PES; The addition of a chilled water storage tank has a negative impact on thesystem’s PES due to additional parasitic loads. The plant system used inScenario 3 is the plant configuration with lowest PES; and Compared to using the cogenerated electricity for own demand, at the currentlevel of grid efficiency, exporting all the cogenerated electricity and importingall the electricity from the grid (Scenario 5) results in a reduction in PES.196