Chiller Sequencing and Load Distribution: Running the Right Number of MachinesMulti-chiller plants must intelligently sequence machines to maximize efficiency. Running one chiller at 80% load is almost always more efficient than running two chillers at 40% load each—but this depends on each chiller’s performance curve. Optimal sequencing is a critical and often underexploited energy-saving lever.Why Part-Load Efficiency Matters for SequencingMost chillers have a sweet spot—typically 70–90% of full load—where they operate most efficiently. Below 30–40% load, efficiency often degrades significantly due to compressor surge risks, hot gas bypass, or unloading mechanisms. Before adding a second chiller, the BMS should confirm that a single chiller operating at higher load will consume less total energy than splitting the load across two machines.Efficiency-Based Sequencing LogicSimple load-based sequencing (e.g., start second chiller at 90% of first chiller capacity) is a blunt instrument. Better practice is kW/ton-based sequencing: the BMS calculates the efficiency of adding another chiller and starts or stops machines only when doing so reduces total plant kW. This requires real-time power and flow measurement on each chiller.Lead-Lag Rotation and EqualizationIn plants with multiple identical chillers, lead-lag rotation ensures even wear and equivalent total operating hours. This also provides redundancy—if the lead chiller fails, the lag chiller takes over automatically. Runtime equalization algorithms in the BMS can automatically rotate the lead machine monthly or by runtime threshold.Free Cooling and Waterside Economizer IntegrationIn climates with cold winters, waterside economizers can provide free cooling when outdoor wet-bulb temperature is low enough. A plate-and-frame heat exchanger connects condenser and chilled water loops, bypassing the chiller compressor entirely. Properly integrated, free cooling can displace hundreds of chiller operating hours per year, with energy savings of 20–40% on annual chiller energy in cold-climate buildings.Pro Tip: Add real-time kW/ton monitoring to each chiller and program the BMS to use efficiency-based sequencing rather than simple load percentage thresholds.