BAS, PAS, and EMCS
Controls are where savings persist or evaporate
A BAS (building automation system) supervises HVAC and plant through DDC controllers and a points list; an EMCS (energy management and control system) is the energy-focused layer - scheduling, trending, demand limiting, and reporting; a PAS (process automation system) covers industrial process control, where the same discipline applies but loads follow production, not occupancy.
Candidates must know the sequences that produce savings: optimal start/stop, night setback and setup, occupancy scheduling with holiday calendars, economizer changeover with a functioning high limit, supply air and static pressure reset, chiller/boiler sequencing and lead-lag, condenser water reset, demand limiting and load shedding, and verified setpoints. Equally important are the diagnostic tools: trend logs, point-to-point verification, sensor calibration, PID tuning, alarm management, and interoperability standards (BACnet, Modbus, LonWorks). Retro-commissioning of controls typically yields 5–15% savings at low capital cost.
Traps. Claiming schedule savings without checking for manual overrides and operator-set bypasses; trusting an uncalibrated sensor (a 3°F bias wrecks a reset schedule); missing simultaneous heating and cooling; assuming an economizer works because the point exists; and counting savings with no trend data to prove persistence.
Worked example
A 60 kW combined lighting-and-fan load runs 24 hours instead of 12 scheduled hours, 250 days per year. Excess energy = 60 kW × 12 h × 250 days = 180,000 kWh, about $18,000/yr at $0.10/kWh - recovered by a schedule fix and override alarms, with essentially no capital.