Context and challenge
Retail load swings with footfall and trading hours, so the plant starts and stops constantly. The existing Johnson Controls BAS was hard to operate and unstable; eight cooling towers ran on fixed staging while the cooling and secondary pumps stayed at fixed frequencies.
Savings could not come at the cost of comfort, and the works had to be completed at night and between trading hours.
What we did
- Platform integration: both BAS consolidated so chillers, pumps and towers are coordinated from one view.
- VFD retrofit: variable speed drives added to the primary chilled-water pumps (cooling and secondary pumps already had VFDs).
- Strategy upgrade: pump frequency optimisation from pipe characteristics, dynamic chilled-water temperature from outdoor temperature, cooling-tower approach control from wet-bulb temperature, plus self-learning tower staging.
- Similar-day verification: separate weekday and weekend comparisons of total plant energy with measures off and on.
Result
Cumulative plant EER improved from 3.0 to 4.4. The cooling season saved about 290 MWh, cutting roughly 278 tonnes of CO₂, with a 20.3% summer saving rate and automation raised to 99%. The two similar-day pairs delivered 23.1% (weekday) and 17.9% (weekend).
Tower and pump sequencing is the most overlooked saving in retail plants. Once the system learns the best-efficiency point it stages equipment itself — consistently, and without depending on who is on shift.
Two similar-day pairs, summer
| Condition | Test date | Peak outdoor | Plant energy | Saving |
|---|---|---|---|---|
| Measures off (weekday) | 2024-07-08 | 38 °C | 19,753 kWh | — |
| Measures on (weekday) | 2024-08-01 | 38 °C | 15,202 kWh | 23.1% |
| Measures off (weekend) | 2024-07-07 | 37 °C | 15,835 kWh | — |
| Measures on (weekend) | 2024-08-11 | 37 °C | 13,150 kWh | 17.9% |
| Summer average | — | — | — | 20.3% |
Tested to GB/T 31349-2014; the average of the two similar-day pairs is reported as the season's saving rate.
Comparable systems,
different results
We keep the full test record and strategy log for this project. If your plant looks similar, start with a measured audit before committing to a retrofit.