A few months ago, this column covered the basics of developing effective control system sequences. You might recall that it discussed the process of how a designer needs to select and describe sequences that provided safe, reliable, and efficient control.
Once a sequence is developed it then needs to be properly implemented, a challenging task that falls to the controls contractor, but interpreting the sequence and programming the system is only one of their many tasks. First, they need to competitively bid and win the project, and then they go through the process of developing the controls submittals and installing the controllers, sensors, and actuators.
Finally, they are at the point where they are ready to interpret the sequence and create the code that gets used in the controllers. The contractor may be installing controls on a new construction project where controls probably are one of the very last items to be completed, or they may be working on a retrofit project where equipment is only shut down for brief intervals while the new system is installed. In either case, the contractor is constrained for time (and let’s be realistic — on budget) to get the program in place, tested, and validated.
The end result, unfortunately, is often a control system that may “work” but is not operating the way that the system designer had intended. This is where the important task of controls system commissioning by either the original controls designer or a third-party commissioning agent comes into play. The purpose of controls commissioning is to go through the system and validate that it is working the way that it was designed. It is not intended as a crutch, or criticism of the contractor, but instead as a quality control measure intended to verify that the system works as it was intended in design.
The process for controls system commissioning begins with a review of the contractor’s test reports. These documents are generally provided by the contractor and show that they have gone through the process of checking wiring, connections, and basic system operation. Ideally, the contractor will also have an updated set of control drawings available for the commissioning agent as well.
After reviewing reports, the commissioning begins with an inspection of control panels, end devices, and equipment to verify the proper component installation. Are the right sensors and actuators installed in the right places? Is wiring properly installed? Are control panels installed in a professional manner and properly labeled? The commissioning then progresses to the controls user interface, verifying that the necessary points are connected and properly reporting at the user interface. System loops should be observed and trended to see if they are operating in a stable manner.
The final step is to start to validate sequences. Much of this can be done through observation and trending, but in many cases, sequences are best verified by simulating changes to inputs and watching if the required outputs change. For example, if the input for outdoor air temperature is reduced from 75˚F to 50˚F, does the boiler come on? Does the hot water loop temperature setpoint reset as the temperature is dropped further?
Commissioning is an iterative process. Once we go through the system, we document our findings into a punch list. The contractor then fixes any issues and the system is then re-tested. Ideally, at the end of the day, we have a system that is properly commissioned and is working the way that the designer had intended.
A system that works as designed is a win–win–win deal. Good for the designer, good for the contractor, and great for the owner! ES