Building Automation and Control Systems
Points, loops, and sequences
Field DDC controllers run local sequences; supervisory controllers handle scheduling, trending, and alarms. Protocols include BACnet, Modbus, and LonWorks, with gateways translating between them. Point types: analog input (temperature sensor), analog output (valve command), binary input (status), binary output (start/stop). A control loop has a setpoint, a process variable, and an output. PID control adds proportional, integral, and derivative action to remove offset without hunting; proportional-only control leaves steady-state error, and overly tight deadbands cause valve and damper hunting. Most savings come from sequencing and reset strategies, not from replacing hardware.
High-value strategies
Scheduling with optimum start/stop, night setback and setup, duct static pressure reset, supply air temperature reset, chilled and condenser water temperature reset, ventilation reset with CO2-based demand control, economizer lockout diagnostics, chiller staging and plant optimization, and continuous trend review. Fault detection and diagnostics and analytics platforms convert trends into persistent savings.
Traps
Questions conflate setback with full shutdown, or assume a CO2 sensor measures ventilation rate directly; it is only an occupancy proxy. Another trap is applying a reset schedule without checking coil and terminal capacity limits, or leaving a hot-water valve and chilled-water valve open simultaneously through a changeover.
Rule of thumb
Roughly 1% heating savings per degree Fahrenheit of night setback over an 8-hour unoccupied period, so a 10 F setback yields about 10% if the building actually coasts down. Controls tune-ups commonly deliver 5 to 15% savings at low capital cost.