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Continuous Commissioning®
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Applying the Continuous Commissioning® (CC® 1) process typically reduces energy cost by about 20% in existing buildings as measured by the methods outlined in the USDOE's International Performance Measurement and Verification Protocol. The CC® techniques developed at the Energy Systems Laboratory involve monitoring and solid engineering analysis of mechanical systems and occupant needs. Increased skills and training are needed to obtain energy savings in buildings today. CC® addresses this need. This branded process can be implemented only by qualified, licensed providers. |
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Over the last 25 years, the building industry has made revolutionary changes: chiller systems have decreased their power requirements by a factor of two, from more than one kW/ton to less than 0.5 kW/ton; the use of variable air volume systems has become common practice; and the use of building automation systems has become the norm, with digital controls increasingly replacing pneumatics. Advances in HVAC technology have greatly improved building comfort and significantly decreased building energy consumption. These advances have also increased the importance of proper operational practices in achieving the efficiency potential of the HVAC systems.
Building commissioning has emerged as the preferred method of ensuring that building systems are installed and operated to provide the performance envisioned by the owner. While most commissioning processes focus on bringing building operation to the original design intent, Continuous Commissioning® (CC®) focuses on optimizing heating, ventilation, and air conditioning (HVAC) system operation and control for the existing building conditions. This is an important distinction.
Based on Continuous Commissioning® results from more than 300 buildings, the average measured utility savings are about 20%, with simple paybacks typically occurring in less than two years. Continuous Commissioning® maintains long-term savings using ongoing monitoring of energy consumption with follow-up commissioning, as needed. It also improves system reliability and building comfort by optimizing system operation and control schedules based on actual building conditions, upgrades the operating staff's skills by allowing direct participation in the CC® process, and reduces O&M costs. |
Texas Capitol Extension Building3 - Built in 1992 as an efficient building and commissioned to design specifications by the contractor. The "before" CC® cost index was $ 1.50 / sq.ft. of conditioned space, resulting in a total energy bill of about $539,000 per year. In 1995, the Continuous Commissioning® implementation provided savings of $144,700 per year or about 27%.
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| Figure 1. Matheson Courthouse. |
Matheson Courthouse in Salt Lake City, Utah - This Energy Star building (Figure 1) was built in 1998 and had a very low energy cost of $1.07 / sq.ft. CC was implemented in 2002 and reduced this cost by 18% with a one year payback while improving comfort and reducing trouble calls. (See the detailed case study)
Starr Building in Austin - An older building, renovated in 1963 with the HVAC system replaced in 1982. This building had such serious comfort and indoor air quality problems that the owner had tried to sell the building. Continuous Commissioning® resolved the comfort and IAQ problems and produced energy savings of 27% ($130,000 per year). |
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The above case histories are just three of many examples of how Continuous Commissioning® results in dramatic savings. Additional benefits can also be realized from the ongoing accumulation of hourly (or sub-hourly) building data. It provides factual data on the building's performance which can be used to accurately identify and resolve problems. This data can also be used to make better decisions when upgrades to the electrical and mechanical infrastructure are implemented. |
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The Continuous Commissioning® Process |
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What is the magic involved with Continuous Commissioning® and why does it produce such superior results? There is no magic; results are obtained through objective evaluations and the use of special purpose software that has been developed over the past ten plus years. CC® engineers find opportunities to make the building work better using minor system hardware changes, and by enhancing the building design and operation. For instance, designers typically put in "safety factors" that result in higher energy usage because oversized systems run at reduced part load. In one building, we found most air handlers were oversized by 30 to 50%. This is a common finding.
Figure 2 shows the key steps in the Continuous Commissioning® process. The CC® Assessment of Step 1 uses a visit that involves site staff and site measured data to develop a price proposal that identifies and quantifies potential measures and savings. It also identifies any additional energy monitoring that may be needed. Upon approval to proceed (Step 2), the CC® provider develops performance baselines for energy and comfort (Step 3).
Step 4 includes examining the building in detail to diagnose operating and comfort problems in the building, identifying specific component failures or degradation, and diagnosing specific causes of system inefficiency down to the AHU and/or terminal box level. The maintenance measures, control changes, balancing changes, or minor equipment improvements needed to improve efficiency are efficiently identified and prioritized. This step involves identification of changes needed to operate the mechanical equipment for optimum efficiency for the actual building use. This fundamentally differs from the traditional commissioning approach that focuses on bringing the building to design conditions that are usually over-designed and often rather different from actual use, resulting in built-in inefficiencies.
Step 5 involves implementing CC® measures, after discussing them with the building staff, and changing the measures as needed to fit the measures to staff expectations. The CC® engineers then work closely with the staff to implement the approved changes, and further fine tune the changes during implementation. Again, this fundamentally differs from retro-commissioning projects that deliver a report to the owner who has staff or a contractor implement the measures. The CC® engineers have the knowledge required to fine tune the measures and often double the savings obtained when others implement the changes. This tunes the equipment to deliver comfort with much improved savings. An important feature of Step 5 is that the building staff is deeply involved in the CC® process.
Finally, Steps 6 and 7 include documenting the changes in operating procedures for the staff as well as the energy savings and comfort improvements. Ongoing tracking of energy and comfort performance is essential to maintain the integrity of the energy savings. Experience has shown system components often fail or degrade in ways that increase operating cost by $0.50/sq.ft.-year. These losses usually go unnoticed since the controls compensate by using substantially more energy to sustain comfort set points. A dedicated CC® monitoring and analysis staff with software tools will identify degradation in savings more efficiently than a group for whom this is just one of their many responsibilities. This investment assures the long term survivability of the savings.
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| Figure 2. The Continuous Commissioning® Process. |
SCOTT M. MATHESON STATE COURTS COMPLEX
Salt Lake City, Utah
PRINCIPAL CONTACT
James Hood, P.E.
Energy Engineer
Office of Resource and Planning
Department of Natural Resources
State of Utah
Salt Lake City, UT 84114
(801) 538-5251
CONTINUOUS COMMISSIONING® STARTED
January 2002
COMPLETED
as of December 2002
PROJECT COST
$75,000
PROJECT SAVINGS
$73,000/year
PROJECT SIZE
420,000 sq.ft. |
Continuous Commissioning® was performed by a team consisting of facility O&M staff, a Utah State energy engineer, a master controls technician, and Energy Systems Laboratory CC® engineers over a one-year period. Measured annual savings were $73,000/year (about 40% from electricity, and 60% from natural gas consumption). The 420,000 square-foot State Courthouse is located near the Utah State Capitol in downtown Salt Lake City. The state-of-the-art complex was opened in January 1998 with full DDC (Direct Digital Control) EMCS on its HVAC system, which includes 6 SDVAV AHUs (525,000 CFM total) and over 500 terminal boxes. Its thermal plant has one 800-ton chiller, one 400-ton chiller, and two 500-hp boilers. CC® measures ranged from optimization of chillers, boilers, and AHUs to underground garage ramp de-icing system operation. A "semi-occupied" mode was developed especially for the terminal boxes to eliminate unnecessary simultaneous heating and cooling, and outside air intake. Winter warm-up period and summer cool-down period operation were studied and optimized, as well as the economizer cycles (including both air side economizer and water side cooling tower economizer) and the primary-secondary chilled water distribution system, etc. Based on facility occupants and management personnel, building comfort has been greatly improved, and trouble-calls dropped significantly. The project simple payback was 1.03 years.
Features
- As one of the State of Utah's "Top Five" Energy Star Buildings before CC®, the Courthouse presented extra challenges to the CC® engineers and team.
- Designed to accommodate 37 courtrooms, a four-story glass rotunda and a two-story common gallery area, the Courts Complex is one of the largest public buildings in the state of Utah.
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1 Continuous Commissioning and CC are registered trademarks of the Texas Engineering Experiment Station. |
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Continuous Commissioning®
