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Glossary
Operations and asset management

What is BMS, BAS, EMS, BEMS?

Definition

BMS and BAS are two names for the controllers and software that run a building's HVAC, lighting and plant to schedules and setpoints; an EMS or BEMS focuses on metering, analyzing and reducing energy.

Which term is used where

BMS is the usual term in the UK, the Middle East and Asia, and BAS in North America; both describe the same class of system. EMS is common among energy teams and portfolio managers, and BEMS is used mostly in the UK and Europe for a BMS with an energy focus. Large hospitals, airports and campuses often run several generations of these systems from different vendors.

Protocols and standards

BACnet, the data communication standard for building automation and control networks, is maintained as ANSI/ASHRAE Standard 135, and the current version, 135-2024, was published on 31 December 2024 per BACnet International. Modbus remains common on meters, drives and plant controllers, so most sites carry both protocols.

Working alongside an existing BMS

Aqueduct can keep the existing BMS and work across it, replace it, or be built in at design stage. It reaches AHUs, RTUs, chillers and VAV boxes through a field device network controller that speaks BACnet or Modbus, and simple loads such as exhaust fans through LoRaWAN relay switches. Where control is enabled, with owner approval, Smart Controls schedules and automates devices, with lockout warnings that prevent short cycling.

Questions

BMS, BAS, EMS, BEMS: common questions

A building management system is the control layer of a building: controllers, sensors and software that switch and modulate plant to keep conditions on target. The same system is called a BAS in North America. Aqueduct can work alongside an existing BMS rather than replacing it.

A BMS runs one building to its sequence. It rarely carries water, air quality, portfolio comparison or a baseline that can prove a saving, so owners add an analytics layer that reads the BMS and other systems together, as explained in BMS vs BEMS vs EMS.

An EMS tracks and analyzes energy across meters and often across many sites. It may not control any equipment at all. Its outputs are baselines, benchmarks and savings reports, which a BMS seldom produces because it is designed around sequences and setpoints.

When controllers are unsupported, spare parts are scarce or the system cannot be integrated with newer equipment. Many owners first add monitoring over the existing system to learn which plant needs attention, then plan replacement. The BMS replacement buyer's guide covers the decision.

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Bring a site, a utility bill or a question. We will show you where the loss is.

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