One, Two & Three Exchange Square and The Forum have recorded a remarkable energy reduction with outstanding performance in retro-commissioning (RCx). The team has made considerable efforts to improve the chiller plant’s efficiency and saved a vast amount of energy each year. During the building’s operation, the original design could not match with the actual building’s load, causing the chiller plant to be inefficiently operated. For example, during the night, the cooling load increased by 12% annually compared with Year 2000. After a detailed study on the actual building load, the chiller plant’s replacement has been carried out, and the automatic optimised chiller staging control has been implemented for better energy efficiency. Apart from enlarging cooling capacity with various different sizes of chillers, the chiller plant’s replacement has also been accomplished with the variable speed drive (VSD) feature, which allows greater flexibility in chiller combination for optimisation.
Furthermore, the whole system of secondary pumps has also been optimised. All secondary pumps have been scheduled to be switched to variable frequency drive (VFD) for better alignment with various cooling loads and flow balances. A differential pressure reset strategy has been applied on the secondary pump system to further enhance chiller plant operation’s efficiency. These two approaches on the waterside chiller plant resulted in over 10M kWh of annual energy saving, which accounted for an overall energy reduction of over 55%, compared with the average energy consumption of waterside equipment between 1990 and 2002.
The airside chiller plant also achieved a significant improvement in energy efficiency by replacing the Air Handling Units (AHU) and through further optimisation. As one of the latest technologies using a modular system, EC plug fans were installed during this replacement work. They were followed by the implementation of several reset strategies, AHU supply and return air temperature and variable air volume (VAV) pressure drop were reset to maximise the efficiency. Also, a night mode of a lower pressure setpoint was installed to save energy from the AHU. As a result, the annual energy consumption of airside equipment in 2019 has achieved an annual saving of 31%, compared with the average consumption between 1990 and 2002. Pinpointing the chiller plant’s inefficiency in One, Two & Three Exchange Square and the Forum, showcases an effective implementation of energy saving opportunities (ESOs) through RCx and achieved a substantial amount of energy savings.
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