PhD Thesis - Energy Systems Research Unit - University of Strathclyde

the model was then compared to a separate set of experimental results fromthat used for calibration purposes.3.3.6.1 Inter-model comparisonKohlenbach and Ziegler in [22, 25] performed a dynamic test on their modelwhereby it was first run at steady-state conditions at rated inlet temperatures andmass flow rates and then subjected to a 10°C step increase in hot water circuit inlettemperature. The results obtained in this experiment indicated that it took around 10-minutes for the hot water temperature to stabilise at the new state, and approximately15-minutes for the remaining chiller parameters to reach steady-state, depending onthe thermal mass involved in each internal component. Replicating this test using thedynamic model, the chiller was supplied at steady, rated conditions (hot water circuitinlet temperature of 75°C with a mass flow rate of 0.4 kg/s, chilled water circuit inlettemperature of 18°C with a mass flow rate of 0.8 kg/s and the cooling water circuitinlet temperature of 27°C with a mass flow rate of 0.7 kg/s). A step increase of 10°Cwas then applied to the hot water circuit inlet temperature. The simulation was run ata resolution of 1 second. The results obtained for the proposed model are very closeto those reported by Kohlenbach and Ziegler, with the simulated hot water circuitoutlet temperature modelled stabilising in 620 seconds. The Kohlenbach and Zieglermodel reached a stable state at around 600 seconds; this is a difference of around 3%.3.3.6.2 Comparison with experimental dataThe chiller model was supplied with minute by minute inlet temperaturemeasurements of the three water circuits entering the chiller from an empirical dataset. The model’s output was then compared to the measured data. Figure 3.8 showshow the results obtained for the chilled water outlet temperature data modelled at 1-minute time resolution compare with the measured chilled water outlet temperaturedata.The modelled data closely follows the measured data with identical time responsepatterns, yielding a maximum and mean error of 0.35°C and 0.09°C between themodelled and measured datasets, respectively. The standard deviation is 0.10°C.124