Open PLCs Enhance Building Automation

• By Frank Bicknell
• Manufacturing Digitalization

Summary

An HVAC company in search of modern machine-control advantages finds an Arduino-compatible open PLC controller is the solution.

Like many modern-day makers and hobbyists, I have always been inspired by the possibilities of high-tech computing and automation. Although my work history has kept me rooted in the practical needs of commercial and industrial control systems, I have been on the lookout for how to merge more capable and open devices into industrial applications.

My love of hands-on field service led me to start Bicknell Heating & Cooling in the Cincinnati area. We support all types of clients with heating, ventilation, and air conditioning (HVAC) needs using mostly traditional products. This article describes how we used modern industrialized Arduino microcontrollers to operate air handlers, chillers, hot water systems, and more.

A multitude of microcontrollers

There are many types of dedicated microcontrollers used to operate equipment, and there are also a variety of programmable logic controllers (PLCs). These all work well, but they lack the openness of today’s general-purpose controllers. When it comes to these “open” controllers, there are many options for consumer- and hobbyist-grade microcontrollers, and some are even mildly “industrialized.”

I tried several types of microcontrollers on various personal projects, such as modernizing the controls on my boat. The flexibility was good, and I could use modern programming languages and methods such as C++ and “sketches,” and the material costs were minimal.

Especially important for today’s applications is the ability to connect mobile devices or a browser to microcontrollers to access data for visualization and analysis. One option is to host web pages right on the controller. Another is to use external software running on a PC or mobile device to access the microcontroller data, and then display and act on it as needed. I experienced good success using the Xojo cross-platform rapid application development environment to do this.

However, even considering the many benefits of microcontrollers, I knew their durability was suspect, and it could be problematic to connect them to the typical voltage and current signal levels used with standard industrial instruments. Nothing I had found convinced me these types of controllers would be suitable for industrial applications.

Finding a tough open controller

After more research, my team and I discovered an industrial automation vendor had developed an Arduino-compatible controller, and packaged it in a form factor compatible with its line of PLC I/O, communication, and other modules (figure 1). Open-source Arduino Software makes it easy to write code and upload it to a compatible computer board.

With this solution from AutomationDirect, users like me can take advantage of modern programming methods and use a specialized graphical programming language included with the controller. We can connect physical sensors and controlled devices using typical industrial signals and proven modules, and even make the most of many types of specialized Arduino “shield” modules for other purposes.

Creating an open building automation system

Our team was already very familiar with using commercially available, proprietary HVAC control platforms, which are reliable but can be expensive and somewhat overspecialized. We also had a good amount of experience with traditional PLCs, which can certainly be used for HVAC control applications. However, after investigating the capabilities of AutomationDirect’s targeted open PLC controller product line, we were confident this Arduino-compatible platform would have the open flexibility we wanted combined with the robust characteristics of established PLC systems.

Our first project was re-automating the HVAC system of a nearby school. HVAC projects need to monitor many types of sensors for temperature, humidity, pressure, airflow, and more. They also need to control devices like solenoids and valves. In some locations, variable speed drives were needed for fan and pump control (figure 2). A variety of control panels were needed, and the team could source all types of necessary devices from one supplier, speeding up design, procurement, and fabrication efforts.

For this project, we automated the following equipment and packaged systems (figure 3):

• 15 air handlers (which are supply fans with heating and/or cooling coils)
• one chiller
• two steam boilers
• four hot water boilers
• several water-supply pumps.

All logic was developed to run within the selected open PLC controllers. The controller logic was well suited for us to create our own temperature control algorithms, including a weather reset functionality that allows the system to adapt to the exterior climate. In many ways, the control results were better than what we had experienced with other common but dedicated off-the-shelf microcontrollers.

A PC running Visual Basic–like Xojo provided a supervisory front end so operators could visualize system function and adjust set points. 

The system was commissioned rapidly, and because the site was an operating school, it was necessary to perform the final cut-ins largely during off hours. We found that I/O checkouts were straightforward, just as they would have been for a PLC. 

The control system has functioned reliably; there is plenty of capacity to expand; and the school personnel have found the system easy to use. We are now using the system for on-site visualization and control. In the future, we can add more controlled systems and even expand operating capabilities. Currently, remote access is accomplished using Google Desktop. This works extremely well, but adding remote access directly to the control platform would have been easy too. Any remote access efforts require careful consideration of cybersecurity.

Modern flexibility, traditional robustness

Sometimes, the best automation engineering answer involves products and solutions that are relatively dedicated, sometimes known as “fit for purpose,” but these solutions are often expensive and inflexible. To address these and other issues, today’s users prefer more modern and open designs that can connect with a variety of other systems, are exceptionally flexible, and have plenty of room to grow.

For the types of HVAC systems that our company regularly automates, we have found this Arduino-compatible open PLC controller platform to be capable and an excellent value. We can use modern programming languages and methods to deliver advanced control, while connecting to all sorts of field devices using proven I/O modules and signaling.

Although our experience with this platform to date has been only with HVAC systems, we are confident its advantages will also be significant for other types of commercial and industrial applications.

RESOURCES
“CPAPs RE-INVENTed into Emergency Ventilators Using PLCs and HMIs”
 “Embedded IEC 61131 is Enabling Industry 4.0 & Industrial Internet of Things”
“Experts Discuss Open Process Automation Issues”


All figures courtesy of AutomationDirect and the author
 

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