PhD Thesis - Energy Systems Research Unit - University of Strathclyde

number of cycles during the cooling season from 2,204 to 1,732 cycles: a seasonalreduction of 21.4%. The addition of a solar water heater in Scenario 4, on the otherhand, resulted in a reduction in the number of switching cycles for all three seasons.The SWH offsets part of the heating energy required to keep the temperature in thehot water storage tank between 65ºC and 75ºC, which therefore results in a lowernumber of switching cycles. A lower number of switching cycles of course has the(beneficial) effect of reducing the system’s maintenance requirement.5.3.2 Auxiliary boilerIn all three proposed plant configurations, the micro-trigeneration system included anauxiliary boiler to cater for periods of peak demands. Table 5.7 shows the resultingseasonal and annual auxiliary boiler fuel consumption for the different scenarios.A first important conclusion that can be drawn, is that compared to the fuelconsumption of the CHP unit, the fuel consumption of the auxiliary boiler waspractically negligible for all scenarios. In fact in none of the scenarios investigateddid the annual auxiliary boiler fuel consumption exceed 0.3% of the CHP unit annualfuel consumption, suggesting that the use of the auxiliary boiler was very sporadic,exclusively to cover for infrequent peak demands. During the simulation process,covering for such peak demands was essential in the process leading to the (integrityof the) mathematical iterative process used by the simulation tool to calculate thesolution concentration of the weak and strong branch in the absorption chiller (Referto Section 3.3.4.3) – value would diverge rather than converge. In real life coveringfor such short instances of peak demands may be superfluous rendering the auxiliaryboiler unnecessary.The only ‘sizeable’ change in auxiliary boiler fuel consumption was caused by theaddition of the chilled water storage tank. The addition of a chilled water storagetank in Scenario 3 High results in an additional cooling demand which needs to besatisfied, resulting in the auxiliary boiler operating for a longer period of time tocover for a higher number of peak demands.182