Credit: Henry Obasi
Ownership is bliss. It’s breathing that new car smell, buying a home in a coveted neighborhood, or experiencing a solid financial return on an investment. In the built environment, commissioning and verification of design can ensure that owners delight in the shine of their building and that their investment returns both financial and sustainable gains. Consider this: At one school in Minnesota designed by DLR Group, commissioning resulted in operational efficiencies and utility cost savings of more than $71,000 a year, and a savings to the environment of approximately 620 metric tons of CO2 annually. That’s bliss.
Through an integrated approach, design teams and owners collaboratively define project goals and objectives related to aesthetics, functionality, and budget at the project outset. Environmentally friendly buildings are expected, if not demanded, in today’s climate. Many owners are setting energy-consumption parameters that are reflected in the facility design. The act of simply setting energy goals is not enough, though; building owners should also validate performance through processes such as commissioning or retro-commissioning.
Owners of newly constructed buildings can use commissioning to measure a facility’s actual performance against its design intent. At its most basic, commissioning can uncover problems, including improper system installation or unanticipated occupant actions that are negatively impacting system operations. Operational changes can then be implemented to enhance both operational and energy efficiency.
To evaluate the performance of existing buildings, owners can use retro-commissioning, which identifies low-cost operational and maintenance improvements to optimize system performance. Many times, a few simple adjustments can improve indoor air quality, enhance occupant comfort, and optimize energy performance.
Both commissioning and retro-commissioning can reassure owners that their systems are operating and interacting optimally.
Design, Build, Validate
In September 2007, Belle Plaine Public School District in Belle Plaine, Minn., opened the doors of the 500-student Oak Crest Elementary School. Minnesota Department of Education guidelines require all schools with construction value greater than $500,000 to be commissioned, and in addition to designing the school, DLR Group also served as commissioning agent for the building.
The goal for Oak Crest Elementary was to build a high-performance system that was designed to exceed Minnesota’s energy code efficiency standards. At the time that Oak Crest was in design, Minnesota’s energy code called for 119kBtu per square foot per year, which is the equivalent of an Energy Star rating of 38.
To set an energy benchmark for Oak Crest, an energy model was created. Energy modeling allows design teams to compare different conceptual designs, and then allows the team, in conjunction with the owner, to select the best option based on price, life-cycle costs, energy savings, and return on investment (ROI). The final Oak Crest energy model predicted an annual energy consumption of approximately 69.7kBtu per square foot per year, equal to an Energy Star rating of 84.
In the upper Midwest, commissioning is done following a year of operation to allow the building systems to cycle through four distinct seasons. This season cycle is essential to obtain an accurate diagnostic of the complete mechanical system. Once completed, the commissioning process determined that Oak Crest was actually consuming approximately 84kBtu per square foot per year, which corresponds to an Energy Star rating of 68, a significant variance from the targeted rating of 84.
Investigation and analysis discovered five system anomalies in the heating plant that were negatively impacting the building’s operational efficiency:
1. Air-handling units were operating when the building was not occupied. Although an automated schedule dictated that these units should be powered off during designated periods when space temperatures were satisfied, the units were still enabled. In many instances, the outside air dampers remained open, allowing cold air to enter the building and to further impact load.
2. Demand-control ventilation was not operating as designed. Large volume, single-zone areas such as the gymnasium were operating using a minimum outside air intake of 30 percent, rather than the average 5 percent.
3. The relief air fans were operating during unoccupied times when the fans should be disabled.
4. Outside air dampers were open during the night setback mode.
5. There was more outside air entering the building than specified by the design, which had followed ASHRAE Standard 62 guidelines.
Belle Plaine Public School District wisely included commissioning services as part of the design services contract. As part of that contract, the contractors executed modifications and repairs to the mechanical and temperature controls system issues identified through commissioning at no cost to the district.
Immediately after the heating system was modified, the district realized positive results. A subsequent evaluation determined that building energy consumption dropped by 14kBtu to approximately 71kBtu per square foot per year, equivalent to an Energy Star rating of 82.
The commissioning process also identified a few deficiencies with the operation of the cooling system:
1. The energy-recovery wheel was not operating during cooling modes.
2. The economizer cooling system was not recognizing the full opportunity to provide outside air for cooling in lieu of using mechanical cooling.
3. Air-handling units were heating during morning cooldown modes, resulting in an additional cooling load that needed to be overcome when the building was indexed to occupied mode.
Once again, after these issues were corrected, the district reaped significant rewards. One year after all heating and cooling system modifications were implemented, DLR Group and the district evaluated Oak Crest’s energy consumption. This time, the building consumed approximately 62kBtu per square foot per year, corresponding to an Energy Star rating of 93, exceeding the original energy model by more than 7 percent. This resulted in Oak Crest using nearly 48 percent less energy than a standard code-compliant building.
The impact of commissioning is not only about energy use and ROI. Through verification, we can ensure that a building and its systems are working as intended, and that indoor air quality and thermal comfort are achieved. Retro-commissioning of older buildings also has its benefits. Whether the intent is to revert the mechanical systems back to the level of operation that the owner enjoyed when the building was new, to fix ongoing issues, or to enhance energy performance, retro-commissioning can allow buildings to perform at their best. Ultimately this elevates the experience of occupants and users of a building.
Dan Munn is senior principal and Michael Lavoie is senior associate in the Seattle and Minneapolis offices, respectively, of DLR Group, an interdisciplinary firm providing architecture, engineering, planning, and interior design services. dlrgroup.com