Why These Terms Matter
Smart buildings sit at the intersection of HVAC, electrical, controls engineering, and IT — which means the vocabulary borrows heavily from all four disciplines and often uses the same word to mean different things depending on context. A "point" means something very specific to a controls engineer and something else entirely to a database administrator. A "sequence of operation" is a legal-style specification document, not just a description of how equipment behaves. Getting these terms wrong in a specification, a submittal, or a commissioning report can create real confusion between owners, integrators, and design engineers who each assume their own definition is universal.
This glossary covers 55 of the most important terms an engineer, facilities manager, or building owner will encounter when specifying, designing, or operating a building automation system (BAS) — organized alphabetically with plain-language definitions and references to ASHRAE, BACnet, and industry standards where applicable.
A
- Alarm — BAS point status
- A notification generated when a monitored value crosses a defined threshold or a piece of equipment reports a fault condition — for example, a discharge air temperature exceeding setpoint by more than a deadband, or a fire/smoke damper failing to prove its commanded position. Alarms are typically prioritized (critical, high, low, informational) and routed to an operator workstation, a mobile app, or an email/SMS gateway. Poorly tuned alarm limits are the leading cause of "alarm fatigue," where operators start ignoring alerts because too many are nuisance alarms.
- Analog Input / Analog Output (AI / AO) — Point types
- An analog input is a continuously variable measured value read into the controller, such as a temperature (°F), pressure (in. w.c.), or humidity (%RH) sensor signal. An analog output is a continuously variable command sent from the controller to a field device, such as a 0–10V signal driving a VFD speed reference or a valve actuator position. Distinguishing AI/AO from binary (on/off) points is fundamental to reading a points list or a BACnet object list.
- Analytics (Building Analytics) — Software category
- Software that ingests time-series BAS trend data and applies rules, statistical models, or machine learning to surface issues automatically — simultaneous heating and cooling, short-cycling equipment, sensor drift, or excess after-hours energy use — without an operator manually reviewing every trend graph. Building analytics platforms (sometimes called FDD platforms) are increasingly required by codes such as California Title 24 and ASHRAE 90.1 Section 6.4.3 for large HVAC systems.
- API (Application Programming Interface) — IT/software term
- A defined set of rules that lets one software system request data from or send commands to another. In smart buildings, APIs let a BAS front end, an energy dashboard, or a tenant app pull data out of the underlying automation system without needing native protocol drivers for every device. REST APIs over HTTPS are the most common pattern for modern BAS-to-cloud integrations.
B
- BACnet — ASHRAE/ANSI/ISO 16484-5
- Building Automation and Control Networking protocol — an open, non-proprietary communication standard developed by ASHRAE specifically for building automation and control equipment, covering HVAC, lighting, life safety, and access control. BACnet defines standard object types (Analog Input, Binary Value, Schedule, Trend Log, etc.) and services (ReadProperty, WriteProperty, Who-Is) so devices from different manufacturers can exchange data without proprietary gateways. BACnet runs over several data links, most commonly BACnet/IP (Ethernet) and MS/TP (RS-485 serial).
- BACnet/SC (Secure Connect) — Addendum to ASHRAE 135
- A newer BACnet data link that uses TLS-encrypted WebSocket connections routed through a hub, replacing the historically unencrypted BACnet/IP broadcast model. BACnet/SC was added specifically to address cybersecurity gaps in legacy BACnet networks — encrypting traffic, authenticating devices with certificates, and eliminating the need for UDP broadcast traffic across IT network segments.
- Binary Input / Binary Output (BI / BO) — Point types
- A binary input is a two-state (on/off, open/closed, proven/not-proven) monitored point, such as a fan status contact or a smoke damper end switch. A binary output is a two-state command point, such as a fan start/stop relay or a two-position valve actuator command. Binary points are the simplest and most common point type on a controls points list.
- Building Automation System (BAS) — General term
- The overall system of sensors, controllers, actuators, network infrastructure, and software used to monitor and control a building's mechanical, electrical, and life-safety equipment automatically. "BAS" and "BMS" (building management system) are used largely interchangeably in the U.S. market, though some specify BMS as the broader term encompassing BAS plus lighting, security, and other subsystems under one supervisory layer.
- BMS (Building Management System) — General term
- See Building Automation System. Some engineers reserve "BMS" for a system that integrates multiple subsystems (HVAC, lighting, fire, security, metering) under a single supervisory front end, while "BAS" refers narrowly to HVAC controls — but usage varies by region and specifier.
C
- Commissioning (Cx) — ASHRAE Guideline 0 / 1.1
- A quality-focused process that verifies and documents that building systems and assemblies are designed, installed, tested, and capable of being operated and maintained to meet the owner's project requirements. For controls specifically, functional performance testing (FPT) is the step where each sequence of operation is exercised point by point and confirmed to behave as specified before acceptance.
- Controller (DDC Controller) — Hardware term
- A microprocessor-based device that reads input points, executes control logic, and drives output points for a piece of equipment or zone. Controllers range from unitary controllers (one air handler or VAV box) to supervisory/network controllers that coordinate multiple unitary controllers and communicate with the front-end software.
- COV (Change of Value) — BACnet term
- A subscription mechanism where a BACnet client asks a device to report a point's value only when it changes by more than a defined increment, rather than continuously polling. COV subscriptions reduce network traffic significantly compared to polling every point on a fixed interval, and are the standard mechanism for real-time trend updates on a graphics page.
D
- Deadband — Controls term
- A range around a setpoint within which no control action is taken, used to prevent equipment from cycling excessively when a measured value hovers near the setpoint. A common example is a thermostat deadband between heating and cooling setpoints (e.g., 68°F heat / 74°F cool) so the same zone doesn't call for heat and cooling back-to-back.
- Demand Response (DR) — Utility/grid term
- A program or automated sequence where a building temporarily reduces its electrical demand in response to a utility signal, grid stress event, or price signal — typically by resetting HVAC setpoints, dimming lights, or shedding non-critical loads. OpenADR (Open Automated Demand Response) is the common open standard used to deliver DR signals to a building's BAS automatically.
- Demand-Controlled Ventilation (DCV) — ASHRAE 62.1
- A ventilation control strategy that modulates outdoor air intake based on actual occupancy (often measured by CO2 concentration as a proxy) rather than a fixed design-occupancy rate, reducing the energy penalty of over-ventilating partially occupied spaces while still meeting ASHRAE 62.1 ventilation requirements.
- Digital Twin — Modeling term
- A virtual, data-connected model of a physical building or system that updates in near-real-time from live sensor and BAS data, allowing simulation, what-if analysis, and predictive analytics against the current state of the actual building rather than a static as-built model. Digital twins range from simple 3D-linked dashboards to full physics-based simulation models used for fault prediction and retrofit analysis.
E
- Edge Device / Edge Computing — Architecture term
- Processing that happens locally at or near the field controller or gateway, rather than sending raw data to the cloud for every calculation. Edge computing reduces bandwidth needs, keeps critical control logic functioning during a network or internet outage, and can pre-process or filter data before it's sent upstream to analytics or cloud platforms.
- Energy Management System (EMS) — Software category
- Software (sometimes a subset of the BAS, sometimes standalone) focused specifically on monitoring energy consumption, benchmarking performance, identifying waste, and in some cases automating load-shedding or optimization strategies. EnergyStar Portfolio Manager benchmarking is a common companion tool to a building-level EMS.
- ENERGY STAR Score — EPA benchmarking metric
- A 1–100 percentile ranking of a building's energy performance compared against similar buildings nationally, normalized for size, climate, and operating hours, produced by EPA's Portfolio Manager tool. A score of 75 or higher qualifies a building for ENERGY STAR certification and is required reporting in many benchmarking ordinance cities.
F
- Fault Detection and Diagnostics (FDD) — ASHRAE Guideline 36 / analytics term
- Automated rules or algorithms applied to BAS trend data that detect equipment operating outside of expected parameters (a stuck valve, a leaking damper, simultaneous heating/cooling, a failed sensor) and diagnose the likely root cause, often before a comfort complaint or energy waste becomes obvious to a technician manually reviewing trends.
- Firmware — Hardware/software term
- The low-level software embedded in a controller, sensor, or gateway that governs its basic operation and communication behavior. Firmware updates can patch security vulnerabilities or add protocol features, and unpatched firmware on legacy field controllers is a recurring cybersecurity finding in BAS security assessments.
- Front End (Operator Workstation / Graphics) — Software term
- The supervisory software application — often web-based — where operators view graphics, trends, alarms, and schedules, and issue overrides across the whole BAS. The front end is not where control logic executes; it's the human interface layer sitting above the field controllers that actually run the sequences.
G
- Gateway — Hardware term
- A device that translates between two different communication protocols — for example, converting a proprietary chiller protocol or Modbus RTU signal into BACnet/IP so it can be integrated into the main BAS front end without a native driver. Gateways are common integration points but also common single points of failure and cybersecurity weak spots if left unpatched.
- Grid-Interactive Efficient Building (GEB) — DOE term
- A building designed and controlled to actively coordinate its energy use with the electric grid — shifting load, storing energy, or curtailing demand in response to grid conditions — rather than operating as a passive, fixed-schedule consumer. GEB strategies combine demand response, on-site storage/solar, and smart controls sequencing.
H
- Haystack (Project Haystack) — Semantic tagging standard
- An open, community-developed convention for tagging BAS data points with standardized semantic metadata (e.g., marking a point as "discharge, air, temp, sensor, ahu") so that data from different vendors and projects can be understood and analyzed consistently by analytics software, without a human manually re-mapping every point name.
- HMI (Human-Machine Interface) — Controls term
- A screen or panel — physical or software-based — that lets an operator view equipment status and issue commands directly at the equipment or on a control room console, distinct from a remote web-based BAS front end.
I
- IoT (Internet of Things) — General term
- Physical devices — sensors, actuators, meters — embedded with the electronics and network connectivity needed to collect and exchange data over IP networks, typically using lightweight, low-power wireless protocols. In buildings, IoT sensors (occupancy, CO2, light level, vibration) increasingly supplement or replace traditional hard-wired BAS points because they're cheaper to install and retrofit.
- Integration — General term
- Connecting two or more otherwise separate systems (HVAC controls, lighting, access control, metering, fire alarm) so they can share data or coordinate actions through a common protocol, gateway, or supervisory platform, rather than operating as isolated silos.
K
- KNX — ISO/IEC 14543-3
- An open standard for building automation, especially common in European residential and commercial lighting/shading/HVAC control, using a decentralized bus topology where devices communicate directly with each other over twisted pair, powerline, RF, or IP without requiring a central controller for basic device-to-device logic.
L
- LEED (Leadership in Energy and Environmental Design) — USGBC rating system
- A widely used green building certification program administered by the U.S. Green Building Council that scores a building's sustainability across categories including energy, water, materials, indoor environmental quality, and site — awarding Certified, Silver, Gold, or Platinum levels based on points earned. Building automation and monitoring-based commissioning both contribute credits toward LEED certification.
- LonWorks / LonTalk — Legacy protocol
- An open control networking protocol developed by Echelon, historically common in building automation before BACnet became dominant, using a peer-to-peer architecture with standardized "network variables" analogous to BACnet objects. Many existing buildings still have legacy LonWorks devices that require gateways to integrate with modern BACnet-based front ends.
M
- Modbus — Communication protocol
- An open serial (Modbus RTU) or Ethernet (Modbus TCP) communication protocol originally developed for industrial PLCs, widely used by chillers, meters, VFDs, and generators as a native protocol. Modbus is simple and vendor-neutral but lacks the standardized object model of BACnet, so integration usually requires manually mapping each register to a meaningful point.
- MQTT (Message Queuing Telemetry Transport) — IoT messaging protocol
- A lightweight publish/subscribe messaging protocol designed for low-bandwidth, high-latency, or unreliable networks — well suited to battery-powered IoT sensors reporting readings periodically to a central broker. MQTT is increasingly used alongside BACnet in modern buildings for wireless sensor networks and cloud data streaming.
- MS/TP (Master-Slave/Token-Passing) — BACnet data link
- A BACnet data link running over RS-485 twisted-pair wiring at speeds typically between 9600 bps and 76,800 bps, using a token-passing scheme so each device gets a turn to transmit. MS/TP is the most common wiring for unitary field controllers (VAV boxes, fan coils) daisy-chained on a trunk.
O
- Occupancy Sensor — Field device
- A sensor (passive infrared, ultrasonic, or a dual-technology combination) that detects the presence of people in a space to trigger lighting, HVAC setback, or plug load control. Modern smart-building occupancy sensors increasingly report analog occupancy counts or dwell time rather than a simple binary occupied/vacant signal.
- OpenADR (Open Automated Demand Response) — DR communication standard
- An open, standardized signaling protocol that lets a utility or grid operator send demand response event signals directly to a building's EMS or BAS, which then automates the load-shed or price-response sequence without manual intervention.
- Override — Operator action
- A manual command that forces a point or piece of equipment to a specific value or state, temporarily bypassing the automatic sequence of operation — commonly used during troubleshooting, testing, or an operator-requested comfort adjustment. Overrides should always include a defined release/timeout so they don't silently persist and defeat the intended control strategy indefinitely.
P
- PICS (Protocol Implementation Conformance Statement) — BACnet document
- A standardized document that a BACnet device manufacturer publishes describing exactly which BACnet object types, services, and data links their specific device supports. Specifying and reviewing PICS statements during design and submittal review is how engineers confirm two devices from different vendors will actually be able to exchange the required data.
- Point — Controls term
- A single monitored or controlled variable in a BAS — a temperature reading, a fan status, a valve command. "Points list" or "point count" refers to the complete inventory of inputs and outputs for a project, which drives controller sizing, network design, and integrator pricing.
- Predictive Maintenance — Maintenance strategy
- A maintenance approach that uses trend data, vibration analysis, or machine-learning models to forecast when equipment is likely to fail or need service, allowing maintenance to be scheduled proactively rather than reactively (after failure) or on a fixed calendar interval regardless of actual condition.
Q
- Q-U-C-C-S Naming (Point Naming Convention) — Naming convention
- Shorthand engineers use to refer to structured point-naming schemes (Quantity-Unit-Component-Context-Sequence patterns and similar conventions, including ASHRAE Guideline 36's standardized point naming) that make point names machine-parseable and consistent across a portfolio, rather than ad hoc labels that vary controller to controller.
R
- Reset (Setpoint Reset) — Control strategy
- A control strategy that automatically adjusts a setpoint (such as supply air temperature or chilled water supply temperature) based on load conditions rather than holding it fixed — for example, raising discharge air temperature reset as outdoor air temperature drops, since less cooling capacity is needed. ASHRAE Guideline 36 defines standardized reset logic (trim-and-respond) widely adopted in modern sequences.
- Retro-Commissioning (RCx) — Existing building process
- The commissioning process applied to an existing building rather than new construction — reviewing current sequences, trend data, and setpoints against the original design intent (or best current practice) to identify and correct control problems and energy waste that have crept in since original commissioning or through equipment changes.
S
- Sequence of Operation (SOO) — Design/specification document
- A written, often legally binding specification document that describes exactly how a piece of equipment or system is controlled — start/stop logic, setpoints, resets, interlocks, alarm limits, and failure modes — in enough detail that a controls contractor can program it and a commissioning agent can test it against the same document. The SOO is one of the most important deliverables in a controls project because ambiguity here causes most controls disputes.
- Setpoint — Controls term
- The target value a control loop attempts to maintain — a zone temperature setpoint, a duct static pressure setpoint, a chilled water supply temperature setpoint. Distinguished from an "alarm limit," which defines when a deviation is flagged, and from a "deadband," which defines the tolerance around the setpoint before action is taken.
- Sub-Metering — Metering term
- Installing additional utility meters downstream of the main utility meter to measure consumption by tenant, floor, system, or end use (lighting, plug loads, HVAC) individually, enabling tenant billing, energy benchmarking granularity, and identification of specific high-consumption systems that a single whole-building meter cannot reveal.
- Supervisory Controller — Hardware term
- A network-level controller that coordinates multiple unitary/field controllers, hosts higher-level sequences (like central plant optimization or scheduling across zones), and typically serves as the communication bridge between the field bus (MS/TP) and the IP backbone connecting to the front end.
T
- Trend Log — BACnet object / data term
- A record of a point's value over time, sampled at a fixed interval or on change of value, stored either in the controller itself or historized in the front-end database. Trend logs are the raw material for commissioning verification, energy analysis, fault detection, and troubleshooting comfort complaints after the fact.
U
- UNS (Unified Namespace) — Data architecture term
- A data architecture pattern where every system in a building (or across a portfolio) publishes its data to one centralized, hierarchically organized broker or namespace, so any application can subscribe to exactly the data it needs without point-to-point integrations between every pair of systems. UNS designs typically use MQTT as the underlying messaging layer.
V
- Variable Frequency Drive (VFD) — Electrical/mechanical device
- A motor controller that varies the frequency (and therefore speed) of the AC power delivered to a motor, allowing fans and pumps to run at only the speed needed to meet current demand rather than full speed with a damper or valve throttling the output — a major source of energy savings and a common BAS-controlled output point.
W
- WELL Building Standard — IWBI rating system
- A certification program administered by the International WELL Building Institute that scores a building's design and operation against health and wellness-focused criteria — air quality, water quality, lighting, acoustics, thermal comfort, and mental health support — as a complement to (not a replacement for) sustainability-focused ratings like LEED.
- Wireless Sensor Network (WSN) — IoT term
- A network of battery- or energy-harvesting-powered sensors that communicate over low-power wireless protocols (Zigbee, Z-Wave, Bluetooth Low Energy, or proprietary mesh) rather than hard-wired connections, commonly used for retrofit occupancy, temperature, and air-quality monitoring where running new low-voltage cable would be disruptive or costly.
Z
- Zero Trust (Network Security Model) — Cybersecurity term
- A network security approach that assumes no device or user should be automatically trusted, even inside the building's own network perimeter — every connection is authenticated and authorized individually. Zero trust principles are increasingly applied to BAS/OT networks because legacy building controls protocols were not designed with strong native security and historically relied on network isolation alone.
- Zone — HVAC/controls term
- A space or group of spaces controlled together as a single unit for temperature, ventilation, or lighting purposes — typically served by a single thermostat or sensor and a dedicated terminal unit (VAV box, fan coil). Zone boundaries drive both comfort outcomes and the granularity of the points list.
Smart Buildings Terms — Quick Reference
| Term | Reference | Plain-Language Meaning |
|---|---|---|
| BACnet | ANSI/ASHRAE 135 | Open BAS communication protocol |
| BACnet/SC | Addendum to ASHRAE 135 | Encrypted, TLS-based BACnet |
| Point | General BAS term | One monitored or controlled variable |
| Sequence of Operation | Design spec | How equipment is controlled, in writing |
| FDD | ASHRAE Guideline 36 | Automated fault detection from trend data |
| DCV | ASHRAE 62.1 | Ventilation modulated by occupancy/CO2 |
| Trend Log | BACnet object | Time-series record of a point's value |
| OpenADR | Grid signaling standard | Automated demand response signal |
| Digital Twin | Modeling term | Live data-connected virtual model |
| Zero Trust | Cybersecurity model | No device auto-trusted on the network |