The challenge
GPO Exchange is a Charter Hall office building in Adelaide's CBD, rated 5.5 stars for NABERS Energy at the time of the project. Its chiller plant already had a central plant optimization (CPO) platform installed. The question was whether a model of this specific plant could find savings the existing platform wasn't capturing.
The plant has four Smardt PowerPax chillers of 615 kWr each, arranged as a lead pair and a lag pair. Each pair has an upstream and a downstream chiller in a series-counterflow arrangement. In this layout the load split between the two machines in a pair sets each chiller's lift, so balancing load between them is a practical lever. In parallel plants it's harder to hold conditions while balancing load.
The saving came from strategy alone. The chillers, the controls and the CPO platform all stayed in place.
Site profile
Verified results
12 months of measurement and verification
The baseline ran from 27 June 2021 to 26 June 2022 (245 days with active cooling). The reporting period ran from 7 November 2022 to 30 October 2023 (284 days with active cooling). Daily plant energy was modeled against daily cooling delivered and weighted average system lift, which is the gap between chilled water supply temperature and outdoor wet-bulb temperature, weighted by cooling load. Carbon uses 0.26 tCO2e/MWh, the NGA Factors 2025 figure for South Australia (0.22 scope 2 plus 0.04 scope 3). Cost savings use $0.22/kWh.
| Outcome | Verified result | Status |
|---|---|---|
| Energy saving | 8.8%: 135,005 kWh measured against an adjusted baseline of 148,010 kWh | Verified |
| Energy saved | 13,005 kWh over the 12-month reporting period | Verified |
| Energy saving after correction | 10.3% from 20 February 2023 to the end of the reporting period | Verified, part period |
| Carbon reduced | 3.4 tCO2e over the 12 months | Verified |
| Cost savings | $2,860 over the 12 months | Verified |
| Baseline model fit | Adjusted R² = 0.981 | Verified |
Verified: measured under IPMVP Option B against the plant's own baseline. Carbon and cost are calculated from the verified kWh at the factor and tariff stated above.
The Exergenics approach
A strategy the chiller manufacturer implemented in the existing controls
Exergenics doesn't write to the BMS. The optimized strategy was issued as a functional description, and Smardt implemented it in the plant's existing controls in November 2022.
Model the plant on its own data
Plant trend data came from the building's data warehousing platform. The facilities team flagged plant nuances that don't appear in trend data, and Exergenics adjusted the modeling constraints to match.
Generate the strategy
The model set chiller staging, the load split between the upstream and downstream chiller in each series-counterflow pair, and a dynamic condenser water temperature setpoint.
Implementation by Smardt
Smardt commissioned the updated control strategy in the existing controls in November 2022. No hardware was added.
Monitor and correct
Ongoing monitoring found an issue in how the condenser water algorithm had been implemented. It was corrected in February 2023, and the saving from 20 February 2023 onward was 10.3%.