// primer
What is a Building Automation System?
A Building Automation System (BAS) — also called a Building Management System (BMS) or Energy Management System — is the network of sensors, controllers and software that runs a building's mechanical and electrical equipment automatically. It keeps spaces comfortable and safe, uses as little energy as possible doing it, and tells people when something is wrong.
Almost every commercial and institutional building — offices, hospitals, schools, labs, data centers, airports — has one. Industrial facilities use the same ideas, often with PLCs and SCADA systems doing the heavy lifting for process equipment.
The core loop: sense → decide → act
01 SENSE
A sensor measures the process variable — a space temperature, a duct pressure, a loop differential pressure.
02 DECIDE
A controller compares it to a setpoint and calculates an output, usually with PI or PID logic.
03 ACT
An actuator, valve or VFD changes the process — and the loop runs again, every second, forever.
Week 1 of the curriculum goes deep on this loop. Everything else — protocols, sequences, analytics — exists to make thousands of these loops work together.
How a BAS is structured
Most systems follow the same layered architecture, from the device on the pipe to the dashboard on the screen.
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04
Enterprise / front end
Dashboards, graphics, alarms, trend history, analytics and FDD. Often a web server or cloud platform used by facility teams, energy managers and service contractors.
e.g. Niagara, Metasys, Desigo CC, WebCTRL, analytics platforms
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03
Supervisory
Network controllers that coordinate many field controllers: schedules, trend logging, alarm routing, global sequences and protocol translation.
e.g. JACE / network engines, BACnet routers, BBMDs
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02
Field controllers
DDC controllers that run the actual control logic for one piece of equipment or a zone, reading inputs and driving outputs every second.
e.g. AHU, VAV, chiller-plant, boiler and unitary controllers; PLCs in industrial plants
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01
Field devices
The sensors and actuators wired to the controllers — what the building can feel and move.
e.g. Temperature, pressure, flow and CO₂ sensors; valves, dampers, VFDs, relays
What it controls
HVAC
Air handlers, VAV boxes, chillers, boilers, cooling towers, pumps and fans — the largest share of most BAS projects.
Lighting
Schedules, occupancy and daylight control, often integrated over BACnet or DALI.
Power & metering
Electric, gas, water and thermal meters; demand limiting and utility reporting.
Life safety interfaces
Smoke control and fire alarm interlocks — monitored or coordinated by the BAS, but governed by life-safety codes.
Plumbing & process
Domestic water boosters, sump and lift stations, process cooling and compressed air.
Access & security
Door schedules and occupancy signals shared with HVAC and lighting.
The languages it speaks
- BACnet
- The open standard for building automation (ASHRAE 135). Runs over IP, MS/TP (RS-485) and now Secure Connect.
- Modbus
- Simple, ubiquitous register-based protocol — common on chillers, boilers, VFDs, meters and PLCs.
- LON, N2 & others
- Legacy protocols still found in existing buildings and migration projects.
- Haystack & Brick
- Data-tagging standards that make points understandable to analytics software.
BAS vs. industrial controls
Commercial BAS focuses on comfort, air quality and energy for occupants. Industrial controls — PLCs and SCADA in water plants, manufacturing and process facilities — emphasize uptime, redundancy and regulatory reporting. The physics, signals and control loops are the same, which is why this program covers both.
Why it matters
- > HVAC is typically the largest energy user in a commercial building.
- > Good sequences and tuning cut energy without new equipment.
- > Trends and FDD find failures before occupants do.
Ready to go deeper?
Twelve weeks, about 8–10 hours a week, from fundamentals to a working virtual plant.
Start Week 1 →