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Persistence in Energy Savings from Retro-Commissioning Measures

By Saranya Gunasingh; Scott Hackel, Member ASHRAE; Xiaohui Zhou, Ph.D., P.E., Member ASHRAE

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©2019 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 61, no. 12, December 2019.

About the Author
Saranya Gunasingh is a senior energy engineer and project manager, Scott Hackel is the director of research and innovation and Xiaohui Zhou, Ph.D., P.E., is senior researcher with Slipstream, Chicago.

Commissioning and retro-commissioning (RCx) are critical steps to ensure that a building performs at its best. But commissioning and RCx are truly effective only if their impacts last over time, which cannot be taken for granted. We took a deep dive into dozens of RCx projects in Illinois to determine long-term persistence of savings from RCx and what drives that persistence.

Retro-commissioning is the process of making low-cost adjustments to an existing building’s operation to improve its energy performance. Most often, these adjustments are changes in sequences of operation in HVAC controls, such as temperature or airflow resets, or scheduling changes. Retro-commissioning is most often implemented over a period of time by a team made up of the RCx consultant, controls technician, and a building operator. Traditionally, once the period of RCx has passed, the consultant departs the team and the controls tech and building operator try to maintain building operation as adjusted by the RCx process. However, building operators and controls techs have objectives other than just energy performance: keeping occupants satisfied, maintaining equipment, and conducting retrofits and replacements. As a result, anything from comfort complaints to simple equipment maintenance can lead to altering or even disabling some RCx adjustments.

When RCx adjustments are altered or disabled, the energy-saving measure in question no longer fully persists. That is, the energy savings from that measure has decreased from what it was when it was first implemented. Persistence is the measure of how energy savings last years after a RCx effort is complete. It is an important consideration because many commissioning and RCx efforts, and often the energy-efficiency programs that support them, are justified based on maintaining the initial energy savings year after year. ComEd, an Illinois utility serving the greater Chicago area, was interested in understanding how well energy savings from its RCx program were persisting; how long they could depend on the savings to last for each customer that went through the program.

Considering the magnitude of energy savings at stake, there has been surprisingly little research on the topic of persistence of energy savings from commissioning or RCx. As a result, one of ComEd’s independent energy-efficiency consultants, undertook a substantial primary data collection effort, ultimately visiting 28 separate buildings and investigating 167 individual measures.

The primary objectives of this study were to:

  • Quantify the persistence of RCx measures.
  • Identify operational factors and energy management characteristics that influence the persistence of savings.
  • Determine how to improve program activities to promote persistence or determine whether RCx follow-up is needed after some amount of elapsed time.

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