Application Guidance: Building Automation Systems

When selecting a BAS, consider the following application guidance.

This guide includes the following contents:


A Building Automation System (BAS) requires many details to select, install, commission, and operate. Professionals looking to replace their BAS or purchase a BAS for a new building must start by collecting information about the building in which they plan to implement the BAS. Next, they should contact one or more BAS manufacturer representative(s) or integrator to complete an audit, create system drawings, create a sequence of operations for each system, and specify the BAS. This information is then used to solicit quotes for the BAS including hardware, software, installation, commissioning, training, testing, maintenance, and data management costs.

The business model for BAS manufacturers varies. Some BAS manufacturers provide complete services that include audits, system drawings, sequence of operations for each system, system specification, sales, installation, commissioning, training courses, testing, maintenance, and data management; while others partner with a building integrator to provide these services. Alternatively, an experienced building engineer can complete some or all these tasks.

Gathering Project Information

Selecting a Building Automation System for a building depends on many variables. The ASHRAE 13-2015 Guideline for Specifying Building Automation Systems is a resource that provides a process for gathering information in the “Defining Project Scope” section. An additional list of questions has been developed to help gather project information, guide your audit, and develop a specification for your BAS. This list is provided in more detailed version of the BAS application guidance available here.

BAS Implementation Considerations

Once you have reviewed and compiled the information above, consider the following criteria when selecting a BAS:

  • Integration Capabilities
  • User Interface and User Experience
  • Installation
  • Remote Access
  • Security and Encryption
  • Grid Service Capabilities

Each BAS implementation consideration category is described below.

Integration Capabilities

BAS integration capabilities are separated into four categories:

  1. Application
  2. Communication
  3. Data intake & utilization
  4. Data output & usefulness

Each integration capability is described below.

1. Application

BASs are designed to integrate with both new-construction and legacy HVAC systems. Some manufacturers offer freely programmable building controllers in their catalog while others have general controllers, application specific controllers, and sensors. It is important to understand the communication requirements for all systems, controllers, and sensors in the building before selecting a BAS. A BAS controller’s application can vary by communication type and physical attributes.

Controller Types

There are three general categories for BAS controllers:

  1. Building controllers
  2. General controllers
  3. Application specific controllers

The BAS implementation considerations for each controller type are described below.

  1. Building Controllers
    A building controller is a general controller that acts as a gateway/router to convert communication protocols to allow system-wide read and write functions. Building controllers are the link between the central computer or network and the building systems, general controllers, application specific controllers, thermostats, sensors, actuators, dampers, and other building components.

    Some BAS building controllers have built-In Input/Output (I/O) terminals, while others are modular. Modular building controllers require a power supply module (normally 24 V AC/DC), a control module that includes the communication ports to the central computer/network, and other BAS controllers and accessory expansion modules. Several expansion modules with I/O terminals may be needed to control large systems. ASHRAE 13-2015 recommends having 15% extra I/O terminals for each data-point type to allow for future expansions.

    Different manufacturers label these I/O terminals in different ways, but the terminals are generally used for Analog Inputs (AIs), Digital Inputs (DIs), Analog Outputs (AOs), and Digital Outputs (DOs).

    Common signal types for AI, DI, AO and/or DO terminals include:

    • 4-20 mA (current)
    • 0-10 V
    • 24 V AC
    • Pulse
    • Thermocouples (resistance)
    • Contact closures (open/closed connection)
  2. General Controllers
    Since general controllers are typically not compatible with expansion modules, the built-in controller I/O quantities and types affect what HVAC system or other building system that controller can control.
  3. Application-Specific Controllers
    Application-specific controllers are BAS controllers that are designed for a specific application, such as:

    • Specific HVAC system controllers (i.e., fan coil unit, chiller, boiler, etc.)
    • Thermostats
    • VAV controllers/actuators controllers
    • Security
    • Lighting
    • Blinds
    • Others

    Some controllers may be shipped with a control program for your application, while others may come with a library of programs to choose from in the software user interface.

2. Communication

It is important to understand the communication requirements for each controller type and any connected sensors.

  • Building Controllers
    The building controller connects to general/application-specific controllers using wired (RJ45 or RS485 connection) or wireless connection types made possible with wireless dongles. The RJ45 connections allow for the following protocols: BACnet (Ethernet or IP), Modbus (TCP/IP) and LonMark (IP). The RS485 connection allows for BACnet (MS/TP) or Modbus (RTU) communication protocols. Zigbee, Bluetooth and EnOcean are some of the common wireless connection types. Proprietary communication protocols vary by manufacturer.

    Legacy BAS, HVAC, or other building systems with proprietary communication protocols may require an additional router/gateway to convert the signal to an open communication protocol that the BAS building controller can interpret.

  • General/Application-specific Controllers
    Communication between the general/application-specific controllers and the thermostat is typically proprietary and uses an RJ style connector and a data cable.

3. Data Intake and Utilization

The sequence of operation is the basis for the control programs that will be implemented during commissioning of the BAS. This will determine what information is read-in and used.

ASHRAE Guideline 36-2018 provides guidance on developing high performing sequences of operations, so consider whether you want these to be incorporated in your building.

4. Data Output & Usefulness

BASs and their associated software have data logging and reporting capabilities. Generally, BASs store data and reports it to the central computer, networked storage, or the cloud.

Alarms, trends, and reports can help identify system malfunctions while also providing the benefits of program and setpoint changes. Some BASs have additional options such as email or text alerts.

User Interface and User Experience

The user interfaces for BASs can vary across manufacturers. There are often multiple programs, user interface types, programming types, and multiple layers of access for each program.

  • Multiple Programs
    BAS manufacturers often have separate programs for their BASs that focus on commissioning new controllers, programming/operation, monitoring, and energy management.
  • User interface Types
    The user interface style varies from manufacturer to manufacturer and software application to application within the manufacturer’s offerings. Some user interface styles include text based and graphical programing.

    • Text based programming involves identifying input/output variables with text and writing text-based expressions to interpret inputs and use math/logic to control outputs.
    • Graphical programing involves identifying input/output variables using pictures or symbols and connecting these with other pictures or symbols with built-in math/logic to control outputs.

Typically, BAS building controllers are mounted in a controls cabinet with communication cables/wires that extend to other sections of the building for communication with application-specific controllers and or sensors. General/application-specific controllers may be mounted directly to the HVAC system that is intended to be controlled, like 1) VAV controller/actuators mounted directly to dampers and 2) wall-mounted thermostats mounted to capture zone level data.

Remote Access

BASs are typically accessed with a computer either directly or through a network, but in some cases can also be accessed through remote terminals and smart phones. Accessing the BAS controls, trends and reports may require an additional software package.

Security and Encryption

Security features are not widely advertised for BASs. Although BASs have a variety of security features, like password requirements, for logging into the system for each different user type and some BASs have more specific security features like encryption, complying with FIPS 140.2, complying with FIPS 201, and having adjustable automatic logout times when no activity is sensed.

Grid-service Capabilities

Some BAS manufacturers mention demand response (DR) capabilities, but generally do not mention energy storage, renewable energy, or microgrids in their product literature. Some BASs have integrated Automated Demand Response (ADR) features, while others require third-party drivers to enable ADR capabilities.

Although controlling energy storage devices, renewable energy systems, and participating as part of a microgrid is not often listed in BAS product documentation, most BAS are programmable and use open communication protocols so they can integrate with nearly any other system. Communication with systems that allow these grid-service capabilities may require additional costs beyond implementing a BAS to control HVAC only.