Saving time and money are two key benefits of an open, interoperable control system. Specifying an open system with good planning and coordination up front saves time and money later during system design and commissioning. Good consulting engineers consider the entire system, not just an individual subsystem, when writing specifications.

Take care to factor in the five key elements of the system architecture:

• The network infrastructure
• The system’s control devices
• The network management tools
• The user HMI
• The enterprise/IT level interface

Along with these elements, system specifiers must design each subsystem, then define the system functionality and the requirements for how each subsystem will share information with the other.

For example, consider an occupancy sensor, which determines if someone is in a particular space, such as a building, train, or parking lot. The sensor does not determine what happens when presence is detected; it merely provides the data. Traditional systems connect the occupancy sensor to the lighting system: Someone enters the space, and the lights turn on. But that information is vitally useful to many other systems. For example, an HVAC system can use the information to provide more air into an occupied space rather than an unoccupied space. A security system can use it to determine if there is presence in a secured area. An elevator system can use it to determine if a car needs to be sent to a floor as a person enters a defined space, even before the person pushes the call button. In a parking lot, occupancy sensor information can be used to brighten or dim the lights depending upon the time of day, but it can also alert security personnel that someone is in an area after hours.

These are just a few examples where one piece of data can be useful to separate subsystems. But far too often, these simple cross-system pieces of data are overlooked when the system is designed. Why? Until recently, specifiers have tended to focus on subsystem design only, not considering the value of integration. Open, interoperable systems now enable more complete system integration with very little extra design effort. The process is relatively straightforward: Start by designing each subsystem, then design the cross-system functionality, and then design the user interface for alarming, scheduling, and data logging.