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- EXTRA EDITION
However, there is a frequently overlooked initiative that can have the most significant impact on energy usage and can set the stage for future efficiency initiatives. Retrocommissioning of existing buildings can have an immediate impact of 10 percent or more on energy use without an investment in capital equipment. With additional modest improvements in infrastructure components identified during the process, gains of 30 percent and more can be realized with a payback period ranging from less than one year to four years.
Retrocommissioning is the process of optimizing an existing building’s system performance to meet the original design intent or current operational needs. It’s a “tune-up” of the HVAC systems that are often operating inefficiently even though they may be well maintained and meeting comfort requirements. The term retrocommissioning refers specifically to the optimization process applied to buildings that were never commissioned when built. The importance of commissioning in both new construction and existing buildings is recognized by the U.S. Green Building Council (USGBC) through its LEED certification program as well as American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). It is accepted as a quality assurance tool to deliver performance, reliability, and efficiency in building systems, and is considered an integral part of all energy-efficient system installations.
We often find that while existing building systems may be operating in a fashion that maintains comfort and air quality, they are rarely performing to their designed effectiveness and efficiency without a commissioning process. This gap in efficiency between operation and performance contributes to wasted energy, increased maintenance, and reduced equipment life throughout the life of the building. While the retrocommissioning process may uncover opportunities to replace or update equipment with more energy-efficient designs, the addition of capital equipment is not considered a requirement of the optimization process.
IMPROVING BUILDING PERFORMANCEThe dynamic nature and complexity of commercial building HVAC systems makes them the perfect target for periodic optimization. Issues such as temperature, humidity, outdoor air percentages, and room pressurization have to be maintained as the load varies due to occupancy and weather conditions. Also, the current needs of a building may be different from when it was originally constructed. For example, when a building was constructed it may have been anticipated that shifts would begin at 7 a.m. but now they may start at 8 or 9 a.m. and the equipment warm-up schedule may need to be adjusted. If equipment is operating when it does not need to, it can add substantially to energy costs.
Energy savings are not the only benefit of retrocommissioning. Reduced occupant comfort issues, improved system reliability and indoor air quality, extended equipment life, and failure prevention are also direct benefits - and a part of overall sustainability. In reality, energy efficiency (and savings) is a natural byproduct of optimal system performance.
PERFORMANCE IMPROVEMENT VS. ENERGY REDUCTIONThere is an important difference between the use of retrocommissioning to improve overall building performance, and those initiatives designed specifically to reduce energy consumption. Facility maintenance groups often take a dim view of energy reduction efforts based on negative past experiences. These experiences are usually the result of energy savings efforts that lead to increased complaints and maintenance issues due to unintended consequences of the actions taken. We find that many energy reduction efforts initiated for the sole purpose of energy savings can have negative long-term consequences due to the limited focus of the effort. Without a detailed understanding of building operational design, these efforts often upset the mechanical balance of the building resulting in increased pressure on the maintenance staff. This is especially true when underlying performance deficiencies are already putting stresses on existing equipment to maintain the internal environment.
Because of this, retrocommissioning programs, such as those provided by Environmental Health & Engineering (EH&E), take a holistic approach towards building operations to ensure that the building systems are performing as intended - meaning that the building equipment is operating in the most efficient manner necessary to support the intended operations. Energy use reduction is a natural consequence of improved performance, as are improved equipment life, improved indoor air quality and comfort, and reduced maintenance issues.
EXAMPLES OF RETROCOMMISSIONING FINDINGSRetrocommissioning brings to light many hidden issues within building systems that are the unintended consequences of building and system changes over time. For example, EH&E collected performance data on one building after completion of a large HVAC upgrade that revealed an unusually high energy requirement. This was traced to two 100-horsepower chilled water pumps unnecessarily turning on at night (and in the middle of December in the Northeast). Because this occurred during unoccupied hours, the facility staff was completely unaware of the condition. The cause was traced to a modification made years before that was intended to alleviate a problem that no longer existed. This undocumented and undetected condition resulted in wasted energy and shortened equipment life. This example highlights both the value of system measurement (metered data in this case) and the fact that system performance can be invisible without a means to make it tangible.
Latent performance deficiencies could also be a product of the original building construction. A recent retrocommissioning effort revealed that thermostats located on uninsulated columns at the perimeter of the building caused reheat coils to be activated during unoccupied hours anytime outside air conditions dropped below 60°F even though space conditions didn’t warrant this activity. This condition existed for five years after construction completion but was “invisible” to the maintenance staff. Real-time data collected during the retrocommissioning effort made this operational deficiency tangible.
Other operating deficiencies frequently uncovered during the process include unnecessary off-hours equipment activity, malfunctioning economizers, deficient pump control, equipment sequencing, building pressurization, coil cleaning, and damper control, as well as simultaneous heating and cooling. The results from a thoughtfully applied retrocommissioning program are improved thermal comfort, enhanced IAQ, extended equipment life, improved system performance documentation, and maintenance staff education, as well as the increased energy savings.
THE RETROCOMMISSIONING PROCESSAlthough we recommend that all buildings undergo a periodic performance review to identify performance deficiencies that are otherwise invisible, two readily available documents can be reviewed that will indicate the presence of sub-par performance: maintenance records and energy bills.
When reviewing maintenance records, we use simple “triggers” or “flags” to indicate the need for retrocommissioning:
• Increased occupant complaints
• Utility usage fluctuation
• Increased maintenance calls
Increased complaints and maintenance calls are the tangible “in your face” actions that may signify a larger underlying problem. Utility data is valuable because there is a broad area of sub-par performance without tangible indicators, and utility data serves as a benchmark or flag for both overall building energy intensity (consumption per square foot) and time of use date (utility energy load profile, when available).
To implement retrocommissioning, EH&E, for example, uses a three-phase process. First, a building performance profile is developed to create a picture of the building’s design parameters, current use, and HVAC system performance. The second phase involves a more detailed engineering investigation and recommendations for improvement. The final phase involves prioritization and correction of equipment and system deficiencies selected by the facilities group. At this point, project priorities can be set to target individual zones, systems, or the entire building based on the projected ROI of the proposed improvements.
Retrocommissioning should initially focus on optimizing the performance of the equipment and systems in place. Upgrades to more efficient equipment and systems can certainly be a recommendation resulting from the performance analysis but should be treated as a separate action. Many of the action items targeted will be of the low-cost variety (e.g., control set point changes and sequence improvements) that will increase operational efficiency and create a short payback period for the retrocommissioning effort. A well-organized plan, clear system operating intent (benchmark for comparison), and a focused analysis will all contribute to minimizing costs while delivering the desired results.
SUMMARYAny sustainability effort typically begins with reducing the energy consumption in existing buildings. One of the most effective ways to reduce energy consumption is to actually improve the building performance by using a retrocommissioning process. By taking this holistic approach to building optimization, the building owner can avoid taking actions that will save energy at the cost of increased maintenance and complaints. And the inherent review of existing systems will provide a more detailed ROI for planning future equipment upgrades.
Publication date: 08/18/2008