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When to Retro-commission?

The idea of retro-commissioning - commissioning an existing building which has not been commissioned before – has gained in popularity over the last few years. Its potential for reducing energy consumption and improving working conditions for building occupants is far greater than capital project commissioning simply because of the numbers. At any given time, there are far more existing buildings than new construction or major renovation projects.

In addition, existing buildings offer a much better opportunity to measure and verify the effectiveness of the commissioning process. Existing buildings have past history that can be compared to post-retro-commissioning operation. New buildings have only the nebulous potential of undefined problems if not properly commissioned.

I am not suggesting that new construction commissioning should not be done, but I am suggesting that a building owner does not need to be designing and constructing something new in order to benefit from the rigor of a commissioning process. 

Is retro-commissioning 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 CANDIDATE FOR RETROCOMMISSIONING?

Most owners of multiple buildings will start with their highest energy consuming buildings. A typical metric for this evaluation is total electrical consumption (KWH) per square foot per year, peak electrical demand (KW) per square foot, 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 retro-commissioning, but if the building owner can solve chronic performance problems at the same time (e.g., 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 which are operated on a standard work week (8 am – 5 pm, Monday-Friday) schedule.

Buildings with mechanical air conditioning (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 retro-commissioning.

New or recently renovated buildings with direct digital control (DDC) systems that were not commissioned as part of the original design/construction project have also proven to benefit greatly from the retro-commissioning process (refer to the February, 2007 Engineered Systems Commissioning column).

OTHER CONSIDERATIONS

Buildings with DDC systems will often have the most potential for hidden problems that can be discovered through a retro-commissioning process. This is primarily because DDC systems are more complex and software-based than local devices such as pneumatic or electric controllers. 

Retro-commissioning a building with a DDC system often takes less effort (time) than retro-commissioning 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.”  Numerous failures can increase energy consumption without negatively impacting building occupant comfort or the industrial process contained within the building.

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 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 FOR RETROCOMMISSIONING?

Buildings in which most of the equipment and systems are either outdated or at the end of their life. In this case it may be better to replace the equipment.

Similarly, retro-commissioning is not intended to fix major equipment malfunctions. That requires an equipment-specific service contractor and/or equipment replacement. Retro-commissioning is a system performance enhancement process and relies on properly operating components within each system.

Buildings in which major system design problems exist. In the simplest terms, retro-commissioning is a process for 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, retro-commissioning is not the answer. Redesigning the systems probably is.

 

Commissioning: Getting It Right

Engineered Systems, August, 2007

by
Rebecca Ellis, PE, LEED AP, CCP, CxA
President
Questions & Solutions Engineering
1079 Falls Curve
Chaska, MN  55318
rteesmag@QSEng.com