Chilled Water Supply Temperature Reset: The Simplest Energy WinChilled water supply temperature (CHWST) reset is one of the most impactful and easiest-to-implement chiller energy-saving strategies. By raising the chilled water setpoint when full cooling capacity is not required, chiller efficiency improves substantially.The Physics Behind ResetChiller efficiency improves as the temperature differential between the evaporator and condenser decreases. Raising the CHWST from 6.7°C (44°F) to 10°C (50°F) reduces the compressor lift, typically improving COP by 2–3% per degree Celsius. In moderate climates, CHWST reset can reduce annual chiller energy consumption by 10–20%.Reset StrategiesThree common strategies exist. Outdoor Air Reset links CHWST to ambient temperature—as outdoor temperature drops, CHWST rises. Load-Based Reset uses a valve position or differential pressure signal: when all control valves are less than 90% open, CHWST is gradually raised. Time-of-Day Reset applies higher setpoints during off-peak or night setback periods. Load-based reset is generally the most reliable, as it responds directly to actual cooling demand.Implementation ConsiderationsBefore implementing reset, audit the coil capacities and valve sizing throughout the system. Undersized coils or improperly balanced distribution systems may not achieve adequate dehumidification or cooling at elevated CHWST. In humid climates, maintain CHWST below the dew point of supply air to ensure proper moisture removal. BMS logic should include a slow ramp rate to prevent system instability.Typical Energy SavingsStudies and field data consistently show 10–20% chiller energy savings from well-implemented CHWST reset. A 500-ton chiller running at 0.6 kW/ton for 3,000 hours per year consumes 900,000 kWh. A 15% reduction saves 135,000 kWh annually—potentially $13,500 or more per year at $0.10/kWh. Reset is typically a zero-capital or low-capital measure with immediate payback.Pro Tip: Implement CHWST reset immediately in your BMS—it costs nothing and is often the single highest-return chiller optimization available.