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Part 1: Retrocommissioning Strategies Help Establish Performance Requirements
By Laurie Gilmer, P.E., CFM, SFP, LEED AP
June 2012 -
The United States has about 4.9 million existing institutional and commercial buildings and another 124.4 million residential buildings. Together, these buildings account for 40 percent of the nation's energy use and 9.7 percent of its water use.
The U.S. Environmental Protection Agency's Energy Star programs estimates buildings can save up to 25 percent on their energy use. One of the more common tools maintenance and engineering managers can use to identify savings in their facilities is commissioning.
An analysis of existing buildings by Energy Star found that among commissioned facilities, the median energy savings was 15 percent. Commissioning for institutional and commercial buildings generally applies to any system within a building. The system goes through a testing and validation process to ensure it operates according to the owner's requirements and the design intent.
Three distinct processes relate to buildings. Commissioning applies to new buildings and systems. Recommissioning applies to existing buildings and systems that had been commissioned. Retrocommissioning applies to existing buildings and systems that were never commissioned.
Retrocommissioning can offer facilities important benefits, and for managers looking for opportunities to deliver benefits to their organizations' bottom lines, that is where the differences start to matter.
The first important difference between commissioning and retrocommissioning is in the establishment of performance requirements. In a new building, the performance criteria are established in the drawings and specifications, which form the basis for testing during commissioning. But when a manager decides to retrocommission a system, the system often has been operating for at least three years and, in many cases, more than 20 years. In that period of time, technicians have changed the original set points; components have been added, modified, and removed, or they have failed; and documentation is hard to find.
As a result, the job of the retrocommissioning agent becomes one of investigating system capabilities and documenting performance requirements so they can be tested.
The second key difference between the two processes involves the responsibility for fixing problems and implementing changes. In a new building, the installer has a contractual relationship to provide a system that performs in accordance with the contract documents. If a problem arises that is within that scope, the installer must fix it.
In retrocommissioning, no system installer is involved. When problems arise, the retrocommissioning agent provides an estimate of impact, often in terms of implementation cost, energy savings, and cost savings. It is up to the manager to decide whether or not to proceed.
The final key difference between the processes is the goal. Where commissioning of new buildings and systems primarily relates to ensuring performance from a contractual perspective, retrocommissioning is more like a building tune-up, with a goal of providing better performance and operational savings in terms of energy, water, and money.
Two essential components of retrocommissioning are building-performance benchmarking and monitoring. After all, if the goal is to improve performance, understanding the baseline of current performance and where a building or system falls compared to similar facilities helps managers identify opportunities to improve and set reasonable expectations.
Managers often find it is a challenge to locate benchmarking-performance data against which to compare their facilities and systems. Two favorites are Portfolio Manager from Energy Star and the Buildings Energy Data Book from the U.S. Department of Energy.
Regardless of whether or not manager can benchmark their facilities against others, monitoring their own facilities' performance is essential. In recent years, submetering technology has drawn more attention, and with good reason.
As managers push to improve the performance of buildings, meter data at the whole-building level is no longer enough. In most buildings, HVAC, lighting, and plug loads make up the majority of energy use. In terms of water use, irrigation, domestic, and processes are the largest users.
Submeters on their own do not inherently save energy or water. They provide data. But the data that they do provide can change behavior. They make occupants think about and look at the resources they use, which can changes their overall approach to using resources. Sub-meters give managers the ability to quantify specific areas of use and usage patterns, which they can use to identify opportunities for improvement.
One favorite tool to use in systems monitoring is building-automation system trending. Trending reports cover such factors as system operating times, temperatures, occupancy, and weather data. Understanding these slices of data and the interrelationships of the trends within the context of a building's operational needs can give managers great insight for improving performance.
Retrocommissioning comes at a price. A typical retrocommissioning program costs about 20-50 cents per square-foot, depending on the complexity of the building systems and the extent of the program. But while that cost might seem expensive, the savings typically provide a payback of less than two years, and they are perpetual. The savings a program delivers by the second year also will be there in the third and fourth years and beyond.
A manager can apply retrocommissioning to anything in a building, but the best value comes from targeting those systems that use a great deal of resources. For most buildings, this means HVAC, lighting, and plug loads. Domestic hot-water systems and processes also can be prime targets, though their impacts are often much less.
Retrocommissioning should not be a one-time event. Its value lies in building a program that promotes understanding of building systems, documentation of performance expectations for future reference, and performance monitoring. Together, these elements will provide the necessary information and framework managers need to improve building performance over time.
Laurie Gilmer, P.E., CFM, SFP, LEED AP, is an associate with Facilities Engineering Associates and leads the firm's building energy management and sustainability services. She most recently is the co-author of the International Facility Management Association's (IFMA) second manual in the Sustainability How-To-Guide Series, EPA's Energy Star Portfolio Manager.
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