What is the difference between a BMS and a BAS?
In practice there is none; both describe a system that monitors and controls building equipment from one platform. BMS is the common term in Saudi Arabia and the Gulf, BAS in North America.
Guide · Building management systems
What is a BMS? A guide to building management systems
A building management system (BMS) is a central control system that monitors and automatically runs a building’s equipment: HVAC, ventilation, pumps, lighting and meters, all on one set of screens with alarms and operating records. This guide explains how it works, what it is made of, and when your building needs one.
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A short definition
It is also called a building automation system (BAS), and the two terms mean the same thing on most projects. Its job is to make building equipment run only when needed, at the right values, and to tell the operations team about any fault as it happens.
A BMS does not replace life-safety systems such as fire alarm and suppression. Those remain independent systems, and the BMS only monitors their status.
How does it work?
A BMS runs a continuous four-step cycle, repeated every few seconds for every piece of equipment in the building:
- MeasureTemperature, humidity, pressure and CO₂ sensors, electricity and water meters, and status points that show whether equipment is running, stopped or in fault.
- DecideDirect digital controllers compare each reading with the required value and the schedule, and work out the response according to the approved sequence of operation.
- ActSignals open and close valves, move air dampers, set fan and pump speeds through variable frequency drives, and start or stop equipment.
- ShowThe operator workstation shows the whole building on screens, stores trend logs, and sends alarms to the people responsible, on site or remotely.
Components of a building management system
| Component | Role | Term |
|---|---|---|
| Sensors and meters | Measure room conditions and energy and water use | Sensors & Meters |
| Field controllers | Run the control logic for each plant item or zone | DDC Controllers |
| Actuators and drives | Move valves and dampers and set speeds | Actuators · VFD |
| Supervisory controller | Gathers the controllers and connects third-party systems | Supervisory Controller |
| Operator workstation | Graphics, alarms, trend logs and reports | Operator Workstation |
| Communication network | Connects the components over open protocols | BACnet · Modbus |
Systems it controls and monitors
- Air handling units, fan coil units and VAV boxes
- Chillers, chilled water pumps and cooling towers
- Exhaust, ventilation and car park fans
- Lighting: on/off, dimming and time schedules
- Water tanks, transfer and sump pumps
- Electricity, water and BTU meters
- Generators, low-voltage panels and UPS units
- Status of fire alarm, suppression and PA systems (monitoring only)
What we connect and how: building systems integration.
Communication protocols: BACnet and Modbus
System components and equipment from different manufacturers talk over open communication protocols. That is what lets equipment from different makers work as one system, and keeps you free of any single manufacturer when you extend or maintain it.
- BACnet: an open protocol designed for building automation, standardised as ASHRAE 135 and ISO 16484-5, running over the network or a serial line
- Modbus: an industrial protocol common in meters, UPS units and generators, running over the network or an RS-485 line
- LonWorks and KNX: usually connected to the BMS through gateways
- Dry contacts: for devices with no communication protocol
Benefits of a building management system
- Lower energy use: equipment runs only when needed, at the right values
- Faults found early, before they become complaints or downtime
- Steady comfort and air quality for occupants
- The whole building managed from one place or remotely
- Operating records that support the Saudi energy code and Mostadam
- Longer equipment life through rotation and fewer running hours
A study for the US Department of Energy estimated that properly tuned controls in commercial buildings can save around 29% of energy use on average. The actual figure varies from building to building.
When does your building need a BMS?
- A new building whose specification calls for one
- An existing building with high energy bills or repeated HVAC complaints
- Server rooms or critical equipment that need round-the-clock monitoring
- A building aiming for a Mostadam rating or a green building certificate
- Several systems on separate panels that nobody watches
- An existing system that is old or not working as it should
What determines the cost of a BMS?
There is no fixed price per square metre; the cost is built on what the building actually needs. The main factors:
- The number of points, meaning the inputs and outputs the system reads or controls
- The number of controllers and panels
- Whether sensors, valves and actuators are in scope or supplied by the contractor
- How many third-party systems need integrating
- The operator workstation, licences and graphics required
- Cabling, containment and installation works
Accurate pricing starts from the IO list or the drawings. Send them to us and we reply with a clearly itemised quotation.
Common questions
What is the difference between a BMS and SCADA?
SCADA is mostly used in industrial plants and distributed networks such as water and power, while a BMS is designed for building services such as HVAC, lighting and energy. Some functions, such as alarms and trend logs, are similar.
What is a “point” in a BMS?
A point is each single reading or command the system handles: a temperature sensor reading is one point, a fan start command is another, and its running status is a third. The point count is the basis of BMS design and pricing.
Can a BMS be installed in an existing building?
Yes. Existing equipment is connected through new controllers, or through its communication protocol if it has one, and the work is phased so the building stays in operation.
Free consultation or a quotation
Send us the drawings or the IO list, or call us directly. We review your project and reply with a clear quotation or the questions we need answered.