Did this ever happen to you? It’s a hot summer weekend and you decide to do a little extra work but you need to run by your office to pick up some materials. You unlock the building and expect it to be warm due to the weekend set back. Alas, the entire building is cooled to 70 degrees and you think, “what a waste of energy”! What could have gone wrong? Answer: A lot.
Building Automation Systems (BAS) have allowed for centralized control of complex heating and cooling systems. It’s a wonderful tool, until it fails to perform as desired. How can a building owner/manager ensure that occupants are comfortable, yet systems are operating efficiently to hold down utility costs? Retro-Commissioning is the answer.
So, what is Retro-commissioning (RCx)?
RCx is a systematic review of an existing building’s control systems in order to keep the facility operating according to the owner’s requirements. It focuses on the controls of the building’s primary energy-using equipment: the HVAC systems. Retro-Commissioning identifies improvements to building controls and other low-cost operational measures. Typically, RCx measures are defined as solutions that have paybacks in less than 18 months in buildings that have a BAS (usually 50,000 SF and above). A study by LBNL showed that Retro-Commissioning provides a median 16% whole-building energy savings with a 13-month payback.
According the EPA’s “A Retro-Commissioning Guide for Building Owners” a RCx study should be done every 3 to 5 years. Other trigger events that would call for an RCx effort include:
- Major changes in the use of space
- Equipment that is on when it need not be
- Sensors not working properly
- Unusually high utility bills
- Fans constantly operating at high speeds
- Too many calls to controls service providers
- New equipment recently added
- Excessive number of occupant complaints
Case Study
Several years ago, an Energy Resources Group (ERG) client, Central Methodist University in Fayette, Missouri contacted ERG regarding a building on campus that had been through a major renovation. They had insulated the building and installed high-efficiency ground-source heat pumps and were unhappy when the expected energy savings didn’t materialize. The building, Classic Hall, was an art and music building that had very specific humidity requirements. Aside from occasional poor humidity control, the space was quiet and comfortable, so the triggering event was persistently high energy usage in the building.
ERG did a Retro-Commissioning study and loads re-evaluation and discovered that the existing equipment was significantly oversized, which impacted the ability to effectively control humidity in the summer and wasted humidification energy in the winter. The controls were essentially programmed for comfort without consideration for energy efficiency. They were flowing too much air, and thus simultaneously cooling, reheating, humidifying, and dehumidifying.
After the implementation of the recommendations from the RCx study, Classic Hall, an all-electric building, reduced their annual consumption of electricity from 579,000 kWh to 259,000 kWh – a 55% savings. Click here for more details.
How is Retro-Commissioning Carried Out?
At ERG, we know that every building is unique, and while there are some cookie-cutter solutions that apply to most buildings, for a building to perform well, the typical boilerplate controls programming needs to be tailored. Once we have a full understanding of interactions between the building systems, we have the vantage point ERG needs to truly optimize your controls programming.
The diagram below gives an overview of the basic flow of an ERG Retro-Commissioning project.
ERG’s Extra Steps
At ERG, RCx Studies are really “RCx+”, as we typically include Building Loads Revalidation, an ASHRAE Level Two audit and EEM list, and equipment life-cycle costing. Together this information is the essence of a master plan for the building. This not only gives our clients what they need for immediate controls reprogramming, but it provides a plan for maintenance and future capital investments.
It’s also our practice at ERG to follow up our RCx projects to verify the actual energy savings against projected savings that were documented as a final report. While the national average for RCx shows a 16% average whole-building savings, it’s been ERG’s experience that our RCx+ efforts often result in 20-40% energy savings.
For clients served by Ameren, ERG is one of Ameren Missouri’s most productive Trade Allies in securing incentive funds to offset the cost of Retro-Commissioning. ERG has an outstanding track record of projecting energy savings and hitting the numbers (or doing better). This history brings credibility to the projections and readily secures Ameren incentive funding to help offset much of the cost of an RCx effort.
In addition to saving energy and reducing utility bills, it’s important to note that the RCx process also provides additional important benefits such as:
- Extended equipment life
- Improved thermal comfort and indoor air quality for occupants
- Increased productivity of occupants
When was the last time you had your building retro-commissioned? Is it about time?
