The challenge
The hospital's four-chiller plant had a fixed condenser water setpoint near 73 °F. On any day above about 60 °F wet bulb the cooling towers could not reach it, so all five tower fans sat at full speed for most of the cooling season.
Exergenics modeled the plant from its own BMS trend data and replaced the fixed setpoint with a condenser water reset that follows wet bulb and load. The site's controls team programmed it into the existing BMS in August 2025. Nothing else on the plant changed.
No black box. No training. No security issues.
Site profile
Verified results
IPMVP Option B, August 2025 to August 2026, 12 months
Savings are the adjusted baseline (what the plant would have used, run as before, for the same cooling and weather) less what it actually used, over the 12 months. The boundary is the four chillers and five cooling tower fans.
| Outcome | Result | Status |
|---|---|---|
| Efficiency improvement | 14.0% less chilled water plant energy, over 12 months | Verified |
| Energy saved | 424,423 kWh, over 12 months | Verified |
| Plant efficiency | 0.710 to 0.611 plant kW/ton, adjusted baseline to measured | Verified |
| Summer saving | 22.5%, June to August 2026, with all 90 summer days below the adjusted baseline | Verified |
| Emissions avoided | 114.6 tCO2e, over 12 months | Verified |
Where the saving landed
Almost all of it is tower fan energy. Plant electricity over 12 months: the adjusted baseline against what the plant actually used.
| Plant electricity | Adjusted baseline | Measured |
|---|---|---|
| Cooling tower fans | 809 MWh | 420 MWh, down 48% (389 MWh less) |
| Chillers | 2,226 MWh | 2,190 MWh |
| Total | 3,035 MWh | 2,610 MWh |
The fan saving is 92% of the total saving. Chiller energy held steady.
Half the fan speed, most of the time
Compared at the same wet bulb and the same cooling load. Before, the fans ran at full speed for more than half of their running time, trying to reach a setpoint the towers could not achieve. After, the median fan speed is 49%. Fan power falls roughly with the cube of speed, so a fan at half speed draws around an eighth of its full power.
| Measure | Before | After |
|---|---|---|
| Share of fan running time at full speed | 53% | 15% |
| Median chiller efficiency | 0.528 kW/ton | 0.525 kW/ton |
| Median chilled water supply temperature | 42.0 °F | 42.0 °F |
Slower fans let the condenser water run a little warmer in hot weather, which would normally make the chillers work harder. Compared at the same wet bulb and load, chiller efficiency is unchanged and the hospital gets the same chilled water.
The Exergenics approach
A condenser water reset, programmed by the site team
Exergenics doesn't write to the building controls. The site's controls team programmed the strategy into the hospital's existing BMS, and nothing else on the plant changed.
Data and documentation
Exergenics modeled the plant from the hospital's own BMS trend data, taken at 15 minute intervals.
Strategy development
The fixed condenser water setpoint near 73 °F was replaced with a dynamic reset that follows wet bulb and load, so the towers can reach their setpoint and the fans no longer sit at full speed.
Strategy implementation
The site's controls team programmed the reset into the existing BMS in August 2025.
Measurement and verification
IPMVP Option B, with the boundary around the four chillers and five cooling tower fans. A baseline model of daily plant energy against cooling delivered and weather was fitted to 459 days before the change (R² 0.95) and used to predict what the plant would have used on each reporting day. Days with no cooling, cold days outside the model's range, and a period of on-site works when the strategy was switched off were left out of the comparison.