IEC 61131-3-based Building Automation System

  • September 06, 2013
  • Beckhoff Automation
  • Case Study

By Bill Lydon, Editor

Beckhoff Automation’s new $8 millionUSA headquarters features a building automation system (BAS) based on Beckhoff‘s own hardware, TwinCAT software, and IEC-61131-3 control logic. The new 44,500 square foot building in Savage, Minnesota opened in May 2013.  During their open house, I toured and reviewed the building automation system with Sree Swarna Potluri, Beckhoff Application Engineer, who was a key team member in the design and implementation of the system.

Potluri explained that the Beckhoff hardware and software provided the ability to freely implement any functions required for the BAS for initial project.  There is also complete flexibility for future enhancements. The system was implemented using Beckhoff’s programmable controllers and software based on IEC 61131-3 and a standard library of building automation functions including lighting control, window shade control, climate control, and energy consumption monitoring. The BAS uses BACnet communication as its backbone plus interfaces to other commonly-used building automation subsystems.


The building is served by seven rooftop units and boilers for hot water heating. Four of the rooftops units serve the warehouse area by supplying air-conditioning and heating. The other three rooftop units (air conditioning only) serve the balance of the building. That same balance of the building is heated with hot water heating coils served by dual boilers with redundant circulating pumps. Potluri explained that each boiler can handle 75% of ‘worst case’ heating design requirements in the event that one fails – an important factor during Minnesota winters.

The building has a weather station on the roof which communicates with the controllers using the Modbus RTU protocol to automatically make temperature adjustments, optimizing HVAC efficiency. The actuators on the Variable Air Volume (VAV) boxes are controlled directly from Beckhoff controllers over the Belimo MP-Bus network interface.

Potluri implemented a hot water reset on the boilers based on outdoor temperature and value positions at the heating coils to optimize energy. Nighttime sub-cooling is used in the summer season to take advantage of off-peak electric rates. Building ventilation control is optimized for occupancy based on input from CO2 sensors.

Lighting Control

The system provides adaptive lighting control for daylight harvesting based on outside natural lighting, time of day schedules, automated window shades, and motion sensors to determine room occupancy. The motion sensors and lighting fixtures are interfaced directly to the Beckhoff controllers using the DALI (Digital Addressable Lighting Interface) communications network. In this configuration, the Beckhoff controllers are the DALI masters providing fully programmable lighting control.

Sun Blinds

The building incorporates automated window blinds for glare control and to reduce heat gain in cooling seasons. Blinds are controlled based on sun position and radiation information from the building’s weather station. The use of automated window blinds is common in other parts of the world and is starting to be implemented in leading new building designs in the United States.


The Beckhoff BAS monitors and sends alarms for maintenance information including exceeding runtime limits and faults. Users can be notified with alarms directly on a computer, via email or other means.

User Interface

The system can be accessed by any computer that is on the building’s Ethernet network or remotely through the Internet, provided the user has the correct password access rights. The building has Beckhoff CP6607 displays built into walls so occupants (with access privileges) can control functions including lighting, blinds, and temperature. The Beckhoff CP6607 is a panel PC with a 5.7-inch display, 640 x 480 pixel VGA resolution, Compact Flash card slot and a Mini PCI slot.

Wall mounted touch screen computers make it easy to make changes for special situations such as off hour meetings.


The controllers for the system are three Beckhoff CX5020 Embedded PCs running Windows XP Embedded.  The PC incorporate a 1.6 GHz Intel® Atom™ Z530 processor that supports hyper threading technology with two virtual CPU cores for more effective execution of software. A key to this application is the freedom to control all aspects of the control program using IEC 6 1131-3.

Beckhoff CX5020 Embedded PC controllers communicate on BACnet mounted in field cabinet with I/O and interfaces to DALI and MP-Bus networks.

After the tour, Potluri introduced Beckhoff’s new BC9191 Building Automation Room Controller which was designed specifically for building automation projects. Unfortunately, the controller was not released in time for use on this project. The BC9191 has dual switched Ethernet ports, RS-485 sub-bus, and the following onboard I/O:

  • 3 Digital contact inputs
  • 3 Analog Inputs 0-10 volt
  • 1 Pt/Ni1000 Analog Input
  • 1 Digital 230 VAC, 10 A, relay output
  • 3 Relay Outputs 230 VAC, 1 Amp
  • 2 Triac Outputs 230 V AC, 1 A
  • 2 Analog outputs, 0…10 V

The BC9191 controller also can accommodate additional I/O expansion using Beckhoff I/O modules for a wide range of I/O and interfaces including EnOcean technology, MP-Bus master, DALI/DSI master and power supply, M-Bus master, LON Bus Terminal, and 3-phase power measurement.

BC9191 incorporates controller and I/O for Building Automation

Bottom Line

Beckhoff showcased the flexibility and performance of their products for building automation systems in their new USA headquarters.  This is not surprising because their products have been used for this purpose in a number of large projects already. Around the world, Beckhoff controllers and software are used for BAS applications in some interesting buildings including Maple Leaf Square in Toronto, Allianz Arena in Munich, and Microsoft Technology Center in Cologne.

The building automation industry has yet to embrace the openness of the IEC 61131-3 software standard for the type of control that is illustrated in this application.

Reference Material

Built-in Success - Integrated Building Automation for Investors, Planners and Technicians

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