The challenge
A university research and laboratory building runs an 800 ton chilled water plant, two 400 TR chillers and two cooling towers, with cooling demand in every season.
Twelve months of BMS trend data showed the plant using 0.81 kW/ton on average, rising to between 1.2 and 4.1 kW/ton whenever load fell below 100 tons.
Two control changes, no new hardware and no live connection to the building.
Site profile
Verified results
Annual, cooling mode, verified to IPMVP Option B
Plant energy, emissions and efficiency before and after the change, stated across a full weather year. Savings cover cooling-mode operation of both chillers and both cooling tower fans. No cost saving is reported for this site.
| Annual, cooling mode | Before | After | Saved |
|---|---|---|---|
| Plant energy (kWh) | 577,495 | 496,663 | 80,832 |
| Emissions (tCO2e) | 209.6 | 180.2 | 29.3 |
| Plant efficiency (kW/ton) | 0.81 | 0.70 | 0.11 |
Savings climb with wet bulb, peaking at 21% in the 65 °F to 70 °F bin. Each bin compares the plant at the same weather and the same cooling load before and after the change. The condenser water reset has the most room to work between 60 °F and 80 °F wet bulb, where the plant spends a large share of its cooling hours. Savings taper toward 40 °F as the condenser water temperature approaches its lower limit.
The largest gains came at part load. Between 50 and 100 tons, specific energy nearly halved across the 60 °F to 75 °F wet bulb range, from around 1.8 kW/ton to 1.0 kW/ton. That is the staging strategy keeping the right chiller count on line for the load actually measured.
At higher loads the condenser water reset does the work. Between 200 and 300 tons at 60 °F to 75 °F wet bulb, a band holding nearly 40% of annual cooling energy, plant kW/ton fell 10% to 16%.
How the result was measured
The measurement boundary covers both chillers and both cooling tower fans. Every 5-minute interval in each period was sorted into a 5 °F wet bulb bin and a 50 ton load bin. Where both periods recorded at least an hour in the same cell, the difference in kW/ton was multiplied by the baseline ton-hours in that cell and summed across the full baseline year.
saved kWh = (kW/ton before − kW/ton after) × baseline ton-hours
Matching on load as well as weather matters because plant kW/ton isn't linear with load. It stops a cooler or lighter reporting period from flattering the result. 95.7% of annual cooling energy falls in conditions measured in both periods. The remaining 4.3% is credited at the measured rate.
What sits outside the figure
Savings are stated against cooling-mode operation only. Intervals in heating mode, and intervals with no load or no plant power, were removed from both periods on the same rule.
Condenser and primary chilled water pump energy is excluded from both periods because the pump power trends were unreliable. Pump configurations and speeds were unchanged between periods, so the exclusion doesn't bias the result.
No chillers, towers or pumps were replaced, and no plant was added between the baseline and reporting periods.
The Exergenics approach
Two changes, issued as a functional description
Model the plant from its own data
Exergenics modeled the plant from twelve months of the building's BMS trend data.
Issue two control changes
A chiller staging strategy based on measured load in tons, and a dynamic condenser water temperature reset that tracks wet bulb, load and the chillers in service, issued as a functional description.
Programmed by the site's own controls team
The facility's controls team programmed both changes into the existing BMS in June 2026. The strategy is static control logic running natively on the site's BMS, independent of Exergenics. Data moved as file exports for modeling and M&V. There is no live connection to the building and nothing for IT to review.
Verify against matched weather and load
Savings were verified to IPMVP Option B by comparing the plant at the same wet bulb and the same cooling load before and after the change.