What you need to know about Building Automation System (BAS)

6 Jan 2023
5 min read
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5 April 2023
5 min read

Building Automation System (BAS), also known as Building Management System (BMS) or Building Energy Management System (BEMS), is an automatic centralized control system that monitors and manages a smart buildings' HVAC (heating, ventilation, and air conditioning), electrical, lighting, shading, access control, security systems, and other interrelated systems. It aims to improve occupant comfort, reduce energy consumption, lower maintenance costs, ensure efficient building system operation, and increase security.

BAS functionality is diverse and includes climate control within a specified range, providing lighting to rooms based on occupancy, monitoring performance and device failures, and providing malfunction alarms to building maintenance staff. A BAS reduces energy and maintenance costs and is found in most commercial, institutional, and industrial buildings constructed after 2000. However, older buildings can be retrofitted with a new BAS.

The characteristics of building management systems

They are mostly implemented in large projects with extensive mechanical, HVAC, and electrical systems. Systems linked to a BAS typically represent 40% of a building's energy consumption; if lighting is included, this number approaches to 70%. BMS systems are a critical component to managing energy demand. Improperly configured BMS systems are believed to account for 20% of building energy usage, or approximately 8% of total energy usage in the United States.

Building automation systems are also linked to access control or other security systems, such as closed-circuit television (CCTV) and motion detectors. Fire alarm systems and elevators are also sometimes linked to building automation systems for monitoring.

Building management systems have also included disaster-response mechanisms such as base isolation to save structures from earthquakes. In more recent times, companies and governments have been working to find similar solutions for flood zones and coastal areas at-risk to rising sea levels.

What are different types of inputs and outputs in BAS?

Sensors play a critical role in a building automation system by measuring various environmental parameters such as temperature, humidity, occupancy, lighting levels, and air quality. These sensors can be either analog or digital and are connected to the BAS controller through input channels.

Analog sensors provide continuous variable data that can be used to control the system's behavior. Examples of analog sensors include temperature sensors, humidity sensors, and CO2 sensors. The data from these sensors are typically represented in voltage or current values and are converted into digital signals by the building automation system controller for processing.

Digital sensors, on the other hand, provide discrete data in the form of binary signals indicating whether a specific event or condition has occurred. Examples of digital sensors include occupancy sensors, light sensors, and motion detectors. These sensors provide the BAS controller with valuable information about the occupancy and usage of the building space.

Controls, on the other hand, are the mechanisms used to regulate and adjust the various building systems based on the data collected by the sensors. These controls can be either analog or digital and are connected to the BAS controller through output channels.

Analog controls regulate the system behavior based on the continuous variable data collected by the analog sensors. Examples of analog controls include variable air volume (VAV) boxes, which control the air supply to different zones based on temperature and occupancy, and lighting dimmers, which adjust the light levels based on the amount of natural light in the space.

Digital controls, on the other hand, use binary signals to turn on or off specific system components based on the discrete data collected by the digital sensors. Examples of digital controls include programmable thermostats, which turn the HVAC system on or off based on occupancy, and automated shades, which adjust the amount of natural light entering the space based on the light levels detected by the sensors.

Overall, the use of sensors and controls in a building automation system (BAS) allows for more efficient and effective regulation of building systems, leading to improved comfort, energy efficiency, and cost savings.

Building Automation System: The Infrastructure

A Building Automation System (BAS) is a centralized, interconnected network of software and hardware components designed to control and monitor the building's mechanical, electrical, and plumbing (MEP) systems. The building automation system infrastructure has three primary components: controllers, sensors and actuators, and user interfaces.


Controllers are small, purpose-built computers with input and output capabilities that control devices found in buildings and sub-networks of controllers. They are grouped into three categories: programmable logic controllers (PLCs), system/network controllers, and terminal unit controllers. Inputs allow a controller to read essential factors like temperature, humidity, pressure, and current flow. Outputs allow the controller to send command and control signals to slave devices and other parts of the system.

Sensors and actuators

Sensors and actuators are the eyes and ears of the building automation system, allowing it to sense the environment and take action as necessary. Sensors are placed in the space or room, the return and supply air ducts, and sometimes the external air. Actuators are placed on the hot and chilled water valves, the outside air, and return air dampers.

User interfaces

User interfaces provide a means for users to interact with the system, either through desktop applications or web portals. These interfaces allow building operators to monitor and control the building automation system, receive alerts, and access system data and reports.

The building automation system has multiple operating modes, including occupancy, morning warmup, and night-time setback. Occupancy mode provides a comfortable climate and adequate lighting based on time-of-day schedules. Lighting can be turned on, off, or dimmed with a building automation or lighting control system. Shading and glazing systems control solar heat gains and glare and contribute to thermal and lighting improvements.

Air handlers mix return and outside air, saving money by using less chilled or heated water, and maintaining healthy indoor air quality. Demand-controlled ventilation adjusts the amount of outside air based on measured levels of occupancy.

Finally, all modern building automation system have alarm capabilities, notifying users of potentially hazardous or costly situations. Alarms may immediately notify users through a computer, pager, cellular phone, voice call, or audible alarm, and all systems keep logs of who was notified, when, and how.

In conclusion

BAS is a crucial system for ensuring efficient building operation while minimizing energy consumption and maintenance costs. It can be integrated with various systems to provide improved security and disaster-response mechanisms. Therefore, it is important to understand the different types of inputs and outputs, as well as the various components that make up a BAS to ensure optimal performance.

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