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Quantifying Retrocommissioning Measures and Ensuring High Persistence Levels: A Conversation With Slipstream

image credit: Joe Zhou, Saranya Gunasingh
Rakesh  Sharma's picture
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  • Mar 29, 2019

How effective are retrocommissioning measures?

Over the years, as energy efficiency has become increasingly important to mitigate the impact of climate change, retrocommissioning has become an effective tactic to achieve emission reduction goals. Utilities have focused their attention on prolonging measure life and ensuring high persistence levels for retrocommissioning projects. Recent legislation has also provided necessary incentives for utilities to make retrocommissioning measures more effective. 

Still much work needs to be done. A recent evaluation study by Slipstream Inc., a Wisconsin - based developer of renewable energy programs, attempted to quantify persistence retrocommissioning measures and identify operational factors and energy management characteristics that characterize high persistence levels. The study won the Outstanding Market Research & Evaluation award at the Association of Energy Services Professionals (AESP) expo earlier this year. 

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I caught up with Saranya Gunasingh, who was the project manager for the study, and Joe Zhou, senior researcher, to learn more about it.

1. Can you explain the context for this study? What benefits does ComEd derive from your research?

Saranya: The goal of the retrocommissioning (RCx) program was to go to buildings serviced by the utility (ComEd) , tune up their control systems and operations, and gather energy savings from improved building operations. The initial RCx program was designed to primarily account for first-year savings. As legislation changed the metric for energy efficiency goals to cumulative persistent annual savings (CPAS) in 2016, knowing how long installed measures continued to provided value became very important. The question of measure life for Retrocommissioning programs motivated this research

Retrocommisioning is also a very time and cost intensive effort, so we want to ensure the savings persist for many years after RCx process is complete. ComEd contracts its retrocommissioning projects to third-party service providers; the initial period of audits, analysis, and developing measure recommendations can take 6-12 months. After the RCx effort, the service providers also evaluate accuracy of their estimates. This is a highly collaborative effort between the utility, service providers and the engineering teams on each site. We want the program and measures to be robust and maximize energy savings for many years post RCx. 

2. How did you go about this study - and how did you gather data and what are some key findings from this study? 

Saranya: We sought to answer two overarching questions in this study: 1) what is the persistence in energy savings for each measure and 2) what qualitative factors influence that persistence?

First, we conducted a comprehensive review of RCx projects that participated in the program 3-6 years ago. We went to 28 sites, and collected data on 167 discrete measures. For each building, we started with a quantitative review, digging into copious amounts of data from Building Automation Systems (BAS) to determine if, and how much, each RCx measure persisted. Where long-term data was unavailable, we investigated controls programming or conducted live functional testing by changing BAS setpoints. Overall, we found a 61% persistence by weighted electric energy savings.

But we weren’t done there— we wanted to understand qualitative factors that can lead to better persistence. We developed an extensive questionnaire and interviewed facilities personnel to understand major changes in the building characteristics, operational and management practices since RCx. We coded this data in a statistical model using R, and tested the data for significant factors influencing persistence. We analyzed 16 different parameters and found that training facilities staff on maintaining RCx measures and having BAS management contracted to an external vendor had the most positive influence on savings persistence.  

2. Do you think the sample size for your literature review was sufficient to draw conclusions? Related to that, why are there variations in data available at different utilities for retro-commissioning measures? Do you consider it an industry problem right now?

Saranya: The first thing that we needed to figure out while evaluating savings persistence was what the life of an RCx measure was. The challenge was both the sample size of the literature reviewing persistence and the inherent methodology. Very few of these studies performed primary research in evaluating saving persistence, instead deriving estimates from other studies and inquiries. As assumptions and extrapolations compound, accuracy diminishes. There is also a real shortage of field data on persistence beyond 1-2 years post RCx. We did not have answers to questions like what happened to persistence over a longer period – say, 6 or7 years. This study aimed to set the record straight. We designed the study based on actual field data to find out retrocommissioning measure persistence over a longer time period.  

The way retrocommissioning programs works is that each utility makes assumptions on what they think is happening. Measure life is assumed to be between two years to 14 years in various programs across the US. But again, these figures aren't based on actual field data or research, and the variation is mostly because of assumptions.  

Joe: In our literature review, we analyzed nine field studies. Those reports studied measures with building sample size between one and 36. So our sample size of 28 is at the high end of all these field studies. Persistence results varied mainly because utility programs and regions were different. Other factors include project implementation and research study methodologies. I would say that our findings were just about average in terms of Useful Life (EUL) for energy efficiency measures. Most studies showed that measured persistence levels in terms of EUL were between five to ten years, with an average of about seven years. Currently there is also no standardized energy-efficiency measure life within the industry. Each utility uses its own technical reference manual (if available) to decide the measures. ASHRAE is attempting to develop standardized measures through a research project right now. It would, of course, help if ASHRAE can come up with standardized measures and every used them for RCx persistence studies.  

 3. 2014 seemed to be an interesting outlier case for low persistence. You've mentioned new staff and physical conditions of the building as possible reasons. Can you expand on how these contributed to low persistence levels during that year, and is it indicative of trends in persistence that potentially impact other program years as well? 

Saranya: Three very large commercial buildings that were part of our study impacted persistence levels for 2014 and caused an unexpected trend in persistence for the program year. The sheer size, vintage, construction (i.e., masonry construction) and higher than average operational intensity of these buildings meant they comprised a large share of overall savings—so any deviation at these buildings translates to less aggregate savings for the portfolio. New staff at the facilities were aware but not yet trained on the specifics of the RCx program. Demands related to occupant comfort led to an override of some measures. These factors are not unique to large buildings or to a particular program year. In fact, our study identified triggers for low persistence. Being aware of these triggers and being pro-active about maintaining optimal building operation will lead to higher savings persistence. Continuous energy performance monitoring will show red flags when issues arise, and help address operational issues without compromising savings.

5. You've mentioned staff turnover as one of the biggest reasons affecting persistence levels. What can be done to counter low persistence? For example, do you think documentation of measures and establishing of handoff protocols might help? 

Saranya: The RCx program has been successful in identifying improvements in building operations and making functional adjustments to achieve those improvements, resulting in significant savings in electricity and natural gas. The service providers already produce a comprehensive report that details measures implemented during RCx, but unfortunately, this great resource is often lost post RCx. We used this report to establish post-RCx baseline performance while evaluating persistence. Our recommendation for improving persistence is, first, to conduct follow up site visit to review measures -  To elaborate, we recommend doing brief follow-up site visits where the service providers do quick checks of installed measures for optimal performance. This provides an opportunity to re-instate measures where possible. A continuous monitoring process, such as a high-level monitoring based commissioning approach, can also ensure that savings are preserved over a longer period of time.    

The second recommendation is to offer elevated support, particularly for sites that show higher occurrence of low persistence factors. Here’s factors that contribute to low persistence: high personnel turnover, because knowledge regarding maintaining RCx measures is lost when new facilities personnel replace trained staff; Second, buildings with major retrofits - when building additions are made and systems are  re-configured, RCx measures to be lost in this big shift. Third, when buildings have an external contract in place for managing the BAS system, there is higher persistence in savings compared to buildings where BAS is managed internally.

When RCx participants have one or more of these low persistence triggers, it warrants additional effort from the program to maintain energy savings.   

Joe: Our study shows which measures may have higher energy impact and are easy to persist. Utilities can focus on implementing them. Regarding other measures that are not easy to persist, they should attempt to alleviate or mitigate the problems. As an example, staff turnover is one of the most important factors influencing persistence levels. Perhaps refresher RCx trainings are needed once every few years for these staff, and the building-owner or manager should put it a higher priority to reduce staff turnover. 

Another case is that of major repair or upgrade (of building energy or control system), which have a negative impact on measures persistence because the original RCx setup may have been changed. In such cases, engineers might want to pay more attention to the original RCx and why the program was designes with these measures in mind. 

To mitigate low persistence due to retrofits and major upgrades, building owners or managers should communicate with teams responsible for the retrofit that RCx has been done on this building and provide them with relevant documents. If necessary, coordinate with the original RCx team to find a solution to keep or improve the energy efficiency measures implemented originally during the major changes. 

6. In your experience, how can organizations optimize their operations for high persistence levels? 

Saranya: Utilities are looking at re-designing energy-efficiency programs continuously to improve energy savings. The programs are typically low or no-cost to the customer, and offers access to engineering teams who will comprehensively identify energy efficiency measures and estimate savings.  RCx programs can be extremely cost-effective and contribute to significant reduction in energy use for commercial customers, as we’ve seen in all participants in this study. The program is free for participants, and commercial customers should definitely take advantage of such opportunities to lower their utility bills. There’s more work to be done on this topic – future program design that includes persistence as a key metric could potentially capture lost savings and make RCx programs even more robust.


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