Commissioning: When to Retrocommission?
Is retrocommissioning for everyone? Is it beneficial for every existing building? How does a building owner decide? The following are a few recommendations and issues to keep in mind when prioritizing buildings in order to obtain the best value from a retrocommissioning effort.
What makes a good building candidate?Most owners of multiple buildings will start with their highest energy consuming buildings. A typical metric for this evaluation is total electrical consumption (kWh)/sq ft/yr, peak electrical demand (kW)/sq ft, therms of gas per year, or a combination thereof.
Another selection criterion has to do with performance of the building systems; i.e., which buildings are considered problematic from an energy systems (HVAC, lighting, compressed air, etc.) perspective? It is understood that energy will be saved as a result of retrocommissioning, but if the building owner can solve chronic performance problems at the same time (comfort complaints, process interruptions, noise, etc.), that can be a strong motivator in the building prioritization process.
Buildings whose systems are currently operated continuously will typically offer better paybacks than buildings that are operated on a standard work week schedule.
Buildings with mechanical A/C (cooling) often provide greater energy savings potential than buildings with only heating systems (except in the most extreme cold climates).
Older buildings which have experienced multiple renovations or system modifications over the years are very good candidates for retrocommissioning.
New or recently renovated buildings with DDC systems that were not commissioned as part of the original design/construction project have also proven to benefit greatly from the retrocommissioning process (refer to the February 2007 “Commissioning”).
Other considerationsBuildings with DDC systems will often have the most potential for hidden problems that can be discovered through a retrocommissioning process. In addition, retrocommissioning a building with a DDC system often takes less effort (time) than retrocommissioning a building with only local controls. The power of the DDC system can be used to trend key performance parameters over time and to view the status of multiple points and devices simultaneously.
Buildings with local pneumatic/electric controls also have great potential for hidden problems due to their lack of central reporting and/or monitoring of the distributed controllers. The older the local controllers are, the more likely they are to be out of calibration or otherwise “broken.”
As implied above, it is more labor intensive to recommission a building with local pneumatic/electric controls than a building with a DDC system. Field investigation and checkout of control system operation takes considerably more time due to the absence of permanently installed monitoring equipment. In addition, the need to install and un-install portable data loggers to graph system performance data over time is quite different than the effort to set up and download trend logs from a DDC system.
What makes a poor building candidate?Retrocommissioning is probably not the answer for buildings in which most of the equipment and systems are either outdated or at the end of their useful life. It may be better to replace the equipment.
Similarly, retrocommissioning is not intended to fix major equipment malfunctions. That requires an equipment-specific service contractor and/or equipment replacement. Retrocommissioning is a system performance enhancement process and relies on properly operating components within each system.
Finally, buildings with major system design problems are poor candidates for retrocommissioning. In the simplest terms, retrocommissioning is a process of fine-tuning equipment and system operation to achieve “like new” operation. If the systems were not designed to meet the building owner’s current performance requirements, redesigning the systems is probably a better solution.