Putting EUI on Trial at the LA Federal Courthouse

Sometimes it’s better to aim low than aim high. This is certainly the case with measures of energy use intensity, or EUI.

What exactly is EUI? Energy Star® defines it as an expression of a building’s energy use per square foot per year. In 2015, the average EUI for courthouses across the U.S. was 118 kBtu (kilo-British thermal units) per square foot per year, according to the AIA. Contrast this average with the first-year validated EUI of the new federal courthouse in Los Angeles: 30.9 kBtu/sf*yr.

Such a low EUI for a large building is rare throughout the U.S., even in California – a state known for its strict energy efficiency standards. It’s not surprising, therefore, that the project has received LEED® Platinum certification and a 2018 top-10 award from the AIA Committee on the Environment (COTE).

How did the design-build team, which included SOM, Clark Construction Group, and Syska Hennessy, attain this EUI? Rob Bolin, senior principal at Syska, offers some insights:

Goal-Setting

In 2012, when the General Services Administration (GSA) held a design-build competition for the courthouse, the defined goal was an EUI of 47 kBtu/sf*yr. The winning entry from Syska and its partners provided an improved EUI of 42 kBtu/sf*yr. After the project was awarded, the GSA’s Region 9 team suggested a new goal of 35 kBtu/sf*yr to meet GSA’s regional energy targets. That meant, says Rob, “a rigorous evaluation where we considered 50 or 60 different strategies, and narrowed them down to about a dozen that would offer the best value from the perspective of life-cycle costs.”

Strategies

One of the resulting strategies the team employed was a faceted form of the fully glazed façade. This design compensated for the building’s orientation, which is aligned with the urban grid, but not the North/South/East/West compass axis. Our solution allowed for more opaque façade surfaces to face East and West, where solar gain and glare are more challenging to control, and for transparent surfaces to face North and South, where solar control is more straightforward.

Thanks to this choice of orientation, the team could better control the solar load, conserve energy, and reduce the peak cooling loads inside the building. This last benefit also made it possible for Syska to downsize the building’s MEP equipment.

Another strategy was the use of a displacement ventilation system. Displacement ventilation delivers conditioned air near the floor to provide comfort cooling directly to the occupants in the lower portion of the space, while using thermal stratification to allow warm room air to be removed at the ceiling. Syska had recently implemented such a system in the Long Beach Courthouse for courtrooms and public circulation spaces, and found that the thermal comfort the system provided would be equally advantageous for the Los Angeles Courthouse. The climate in Los Angeles is slightly different from that of Long Beach, but similar enough that in both cases, you can use air-side free cooling for a significant number of hours throughout the year, resulting in an energy-efficient and thermally improved indoor environment with superior air quality.

The GSA and the U.S. Marshall service have very specific air change requirements for holding areas to manage air quality – both central holding areas and local holding areas adjacent to courtrooms. To meet these elevated air-change rates, the team used a “cascading ventilation” strategy. This method takes previously conditioned return air from the courtrooms, mixes it with tempered outside ventilation air, and then delivers the “cascaded” air to the holding rooms at the required air change rates. This technique reduces the amount of energy needed to pre-condition outdoor ventilation air by up to 50%.

For the main lobby, the team chose a changeover radiant slab, using tubing installed in the concrete slab to deliver heating and cooling to this monumental space.

Lighting was another important consideration. “The building’s orientation and massing drove daylight from the perimeter and the central light court into the courtrooms,” says Rob. “So we ended up with balanced daylight on both sides of each of the courtrooms.” The combination of daylight-responsive lighting controls with an all-LED lighting design also results in significant energy savings without any sacrifice in lighting quality.

The next step was to optimize the cooling and heating generating systems, so the team chose condensing boilers, which operate efficiently with low emissions equipment. Other cooling and heating features include high-efficiency centrifugal chillers and a heat-recovery/heat-pump pony chiller that is the first-on chiller. The latter can reject heat to the heating water circuit instead of to a cooling tower and operate simultaneously as a boiler.

Rob notes: “It’s an extremely efficient way for us to operate a plant in a climate like Los Angeles. In this case, we have large parts of the building that rely on 100% outside air for free cooling, but some internal parts that require air conditioning year-round.”

The team also employed photovoltaics, installing a rooftop photovoltaic array that generates 500,000 kilowatt hours of energy each year, which roughly equates to 2.5 kBtu per square foot per year. The system wasn’t energized during the first year of operation, but even without this deduction, the team’s design-phase energy model projected an energy performance of 32.5 kBtu/sf*yr.

Testing: The Moment of Truth

After construction, the team was ready to test the model and validate the EUI by measuring the actual energy performance of the building. The results would not only be enlightening; they would also affect the team’s remuneration: A performance guarantee was a stipulation of the contract with the GSA.

Validation involved the collection of monthly energy bills and metering. Once a quarter, the team would compare the design energy model with the validated energy model. In creating the validated models, the team took into consideration operational adjustments made to the building and actual weather data. (Temperatures, the team discovered, were about six degrees higher than the 40-year averages, which didn’t help on the energy-efficiency front.)

The result of 30.9 EUI after the first year is remarkable, especially considering that the photovoltaic array was not in operation. “We’re likely to attain an EUI under 30 for the second year,” Rob predicts. “That’s phenomenal for a 600,000-square-foot building that adheres to the GSA’s very stringent operational requirements.”

The Syska/SOM/Clark team had even higher performance aspirations from the start – Potentially, the courthouse could eventually become a net-zero building, or even a net-positive energy building, which generates more power than it consumes. “We actually set the building up for this possibility as part of the original competition submission,” Rob says. For example, in the future, the building could use biofuel trigeneration instead of natural gas trigeneration, and add a biofuel generator or a fuel cell generator. Farther down the line, the building could implement new technologies that haven’t yet been developed.

In the meantime, the quest to attain an EUI below 30 continues. Stay tuned for updates!

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