Reference

Building Technology Glossary

50 terms that come up in BMS projects, integration work and energy discussions, explained in plain language.

A

Air Handling Unit (AHU): The equipment that conditions and moves air through a building: fans, filters, coils and dampers in one housing. Most of a BMS sequence of operations is written around how the AHU responds to zone demand.
Analog Input / Analog Output (AI / AO): Point types that carry a continuous value, such as a temperature reading (input) or a valve position command (output). Their binary counterparts, BI and BO, carry on/off states.

B

BACnet: An open data communication protocol for building automation, maintained as an ASHRAE and ISO standard. It defines how controllers describe their data as objects and how they exchange it.
BACnet MS/TP: The serial version of BACnet, running over RS-485 twisted pair. Common at the field level for VAV boxes and unitary controllers; slower than BACnet/IP and sensitive to wiring and addressing mistakes.
BACnet Secure Connect (BACnet/SC): An addition to BACnet that carries traffic over TLS-encrypted WebSocket connections with certificate-based authentication, addressing the lack of security in classic BACnet/IP.
Brick Schema: An open semantic model that describes building equipment, points and the relationships between them, so software can understand that a sensor measures the supply air of a specific AHU.
Building Automation System (BAS): The controllers, network and software that monitor and control mechanical and electrical systems. Often used interchangeably with BMS.
Building Management System (BMS): The supervisory layer of building automation: graphics, scheduling, alarms and trends across HVAC, lighting and other systems. Some people use BMS for the whole system and BAS for the controls underneath.

C

Chiller: A machine that produces chilled water for cooling, either water-cooled with a cooling tower or air-cooled. Chiller plants are usually the largest single electrical load in a large commercial building.
Commissioning (Cx): The process of verifying that building systems are installed and perform as designed. Good commissioning includes functional testing of sequences, not just checking that equipment powers on.
Controller (DDC): A direct digital control device that reads inputs, runs control logic and drives outputs. Ranges from a small unitary controller on a VAV box to a programmable plant controller.
Current Transformer (CT): A sensor clamped around a conductor to measure current for energy metering. Choosing a CT rated far above the actual load is one of the most common causes of poor metering accuracy.

D

Demand Charge: The part of a commercial electricity bill based on the highest power drawn during a billing period, rather than total energy used. A single short peak can set the charge for the whole month.
Demand-Controlled Ventilation (DCV): A strategy that adjusts outdoor air to actual occupancy, usually measured with CO2 sensors, instead of ventilating for full design occupancy all day.
Demand Response: Reducing or shifting electrical load when the grid operator or utility asks, often in exchange for payments or lower tariffs.
Digital Twin: A digital model of a building linked to live operational data. Useful twins combine geometry, equipment relationships and real-time points; a 3D model alone is not a twin.

E

Economizer: A damper and control arrangement that uses cool outdoor air for free cooling when conditions allow. Stuck or poorly controlled economizers are among the most frequent faults found by FDD tools.
Edge Computing: Processing data close to where it is produced, on a gateway or local server in the building, instead of sending everything to the cloud. It reduces latency and keeps local control working during internet outages.
Energy Management System (EMS): Software and metering focused on measuring, analyzing and reducing energy use. It may sit on top of a BMS or be a separate system.

F

Fan Coil Unit (FCU): A small terminal unit with a fan and a heating and/or cooling coil serving one space, common in hotels, apartments and offices.
Fault Detection and Diagnostics (FDD): Software that analyzes BMS and meter data with rules or models to find equipment faults and control problems, ideally before occupants notice them.

G

Gateway (Protocol Converter): A device that translates between protocols, for example exposing data from a manufacturer-specific HVAC bus as BACnet or Modbus points.

H

Heat Pump: Equipment that moves heat rather than generating it, providing heating and often cooling. Commercial heat pumps are central to most building electrification plans.

I

Indoor Air Quality (IAQ): The condition of indoor air in terms of CO2, particulates, volatile organic compounds, humidity and temperature, and its effect on comfort and health.
Interoperability: The ability of systems from different suppliers to exchange data and work together without custom development on every project.
Internet of Things (IoT): Networked sensors and devices that report data or accept commands over IP or low-power wireless networks. In buildings, typically occupancy, environmental and asset-tracking sensors.

K

KNX: An open standard for home and building control, widely used for lighting, shading and room control, especially in Europe.

L

LoRaWAN: A low-power, long-range wireless network protocol. Suited to battery sensors that send small amounts of data, such as temperature or occupancy, across large buildings.

M

M-Bus (Meter-Bus): A European standard for reading utility meters (heat, water, gas and electricity) over a two-wire bus or wirelessly.
Matter: An open connectivity standard for smart home devices that runs over IP networks such as Wi-Fi and Thread, designed to make devices from different makers work together.
Modbus (RTU / TCP): A simple, widely supported industrial protocol for reading and writing registers. RTU runs over serial lines; TCP runs over Ethernet. It has no built-in data model or security.
MQTT: A lightweight publish-and-subscribe messaging protocol common in IoT platforms. Devices publish to topics on a broker, and any authorized application can subscribe.

O

Occupancy Sensor: A sensor that detects whether a space is in use (presence) or how many people are in it (people counting). The two answer different questions and are often confused in specifications.
Open Protocol: A communication protocol whose specification is publicly available, so any manufacturer can implement it. Being open does not guarantee that two implementations will work together without testing.
Operational Technology (OT): Hardware and software that monitor and control physical equipment, as opposed to IT systems that handle data. Building controls are OT and need their own security approach.

P

PID Loop: The proportional-integral-derivative control logic used to hold a value, such as supply air temperature, at a setpoint. Poorly tuned loops cause hunting, wasted energy and wear.
Point: A single data item in a BMS, such as a temperature, a status or a setpoint. A large building can have tens of thousands of them.
Point Naming Convention: The agreed structure for naming BMS points so that people and software can tell what each one is and where it belongs. Inconsistent naming is a common reason analytics projects stall.
Project Haystack: An open initiative that defines tags and conventions for describing building and equipment data, making it easier for software to interpret points without manual mapping.
Proprietary Protocol: A communication method controlled by a single manufacturer. Integrating it with other systems usually requires that manufacturer's gateway or published interface.

R

Retrofit: Upgrading systems in an existing building, for example replacing controls or adding sensors, while the building is usually still occupied.

S

Sequence of Operations: The written description of how a system should behave in every mode: start-up, normal operation, alarms and shutdown. It is the reference for programming and for commissioning tests.
Setpoint: The target value a control loop tries to maintain, such as 22 °C room temperature or a duct static pressure.
Smart Building: A building whose systems share data and are managed together to improve comfort, efficiency and operations. The label means little unless the data is actually used.
Submetering: Measuring energy or water use below the main utility meter, by tenant, floor or system, for billing or operational insight.
Supervisory Controller: A device that sits between field controllers and the BMS front end, handling network management, schedules, alarms and trend storage for a building or a section of it.

T

Thrive Score™: The BuildingTech Insights rating framework that scores technology solutions on seven criteria, from compatibility to value and ROI, to make comparisons consistent.
Trend Log: A record of a point's values over time, kept by a controller or the BMS. Trends are the raw material for troubleshooting and analytics, so their intervals and retention matter.

V

Variable Air Volume (VAV): A system that varies the amount of supply air to each zone with a damper in a terminal box, rather than varying air temperature alone.
Variable Refrigerant Flow (VRF): A heat pump system that circulates refrigerant directly to multiple indoor units and varies the flow to match each zone's demand. Integration with a BMS usually goes through a gateway.