PhD Thesis - Energy Systems Research Unit - University of Strathclyde

Time – basedcontrol scheme00.00-08.00 Hours Valve varies between fully open and fully closed whenair temperature varies between 24ºC-21ºC respectively.08.00-15.00 Hours No control15.00-24.00 Hours Valve varies between fully open and fully closed whenair temperature varies between 24ºC-21ºC respectively.In general, the control scheme used for the 6 household building is similar to thecontrol scheme used for the 3 household building, however the operating times of thecontrols actuating the chiller, the CHP and the bypass valves of the cooling andheating coils were adjusted to reflect the different operating periods imposed by thedifferent (time-sensitive) thermal demands of the 6 household building.3.3 The absorption chiller modelTo facilitate the dynamic modelling of trigeneration systems, a dedicated dynamicchiller model had to be developed for ESP-r. The chiller model described representsa single-effect hot water fed lithium bromide-water absorption chiller, the most apt[15] for use in CCHP trigeneration systems, however the same rationale can beextended to other chiller setups. The pragmatic, yet fully-dynamic model describedwas designed to be easily calibrated using data that can be obtained by measurementsof inflows and outflows to a chiller, without resorting to intrusive measurements,thus greatly reducing the complexities involved and simultaneously increasing themodel’s flexibility. The model described here builds upon the work done byBeausoleil-Morrison et al. [16] who developed a steady state chiller model for thetool.3.3.1 The absorption chiller cycleContrary to a vapour compression cycle which relies on an energy-intensive processof compressing the refrigerant vapour exiting the evaporator through the use of acompressor, an absorption refrigeration cycle relies on the affinity between twoliquids to dissolve the refrigerant inside a liquid solution which can then be pumped,in a less energy-intensive process. Figure 3.3 shows a schematic of a single-effect hotwater fed chiller showing the associated external (dashed lines) and internal (solidlines) flows inside the chiller. The external flows constitute the feed flows, that is,the hot, chilled and cooling water circuits, whilst the internal flow is the cycle103