What Is a Building Automation System (BAS)?
A building automation system is the centralized controls network that operates the building's HVAC, lighting, security, and energy systems — sensors, controllers, and software working as the building's nervous system. The BAS is where designed efficiency becomes actual efficiency: the best HVAC design wastes energy with bad controls, and a good BAS can cut a building's energy use 15-30%. The MEP engineer designs the sequences; the controls contractor programs them.
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What the BAS controls
HVAC (equipment scheduling, setpoints, economizer operation, demand-controlled ventilation), lighting (occupancy, daylight harvesting, scheduling), and often access control, metering, and alarm monitoring. Modern BAS uses open protocols (BACnet) so equipment from different manufacturers interoperates — proprietary lock-in is the legacy problem. The points list (every sensor, actuator, and monitored value) defines the system's scope.
Sequences of operation
The sequences are the engineering: written logic describing exactly how the systems respond to conditions (when the economizer opens, how supply air temperature resets, the morning warmup routine, what happens on a freeze alarm). Poor sequences are the number-one cause of the efficiency gap between designed and actual building performance. ASHRAE Guideline 36 publishes standardized high-performance sequences — specify them rather than letting each contractor invent their own.
Commissioning and analytics
Controls commissioning verifies every sequence works as written — the step most often skipped and most correlated with energy waste. Ongoing: fault detection and diagnostics (FDD) software monitors the BAS data continuously, flagging stuck dampers, simultaneous heating and cooling, and schedule overrides — the faults that silently waste energy for years. Budget the BAS at 3-8% of the MEP cost; it returns multiples in energy savings.
The bottom line
The BAS operates HVAC, lighting, and building systems via BACnet controls — specify ASHRAE Guideline 36 sequences, commission every point, and add fault detection. Good controls save 15-30% of building energy.
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