When the critical infrastructure systems in our building were reaching the end of their useful life, we realized that we had a choice to make: Simply replace the systems to ensure that they could continue to serve AGU’s operational requirements, or challenge ourselves to live out AGU’s mission of “science for the benefit of humanity.” For an organization like AGU, it was an easy decision to make.
In addition to finding ways to showcase our members’ work, be a physical embodiment of the spirit and values of scientific discovery, and help us inform the public about the positive impact our science can have on society, we challenged our project partners—Hickok Cole Architects, Interface Engineering, Skanska, and owner’s rep MGAC—to design the renovation to meet a net zero energy goal: an unprecedented sustainability goal for an urban office retrofit typically reserved for new construction.
You may have already read about some of the innovative technologies and renewable power generation that could be a part of our net zero design. But how do these design strategies work together to create a net zero effect? Let’s start at the beginning.
One of the key metrics used to measure a building’s total energy use and evaluate ways to reduce overall energy consumption is called the energy use intensity (EUI) indicator. It’s calculated by dividing the total energy consumed by the building in one year by the total gross floor area of the building, and is typically expressed in energy used per square foot of building footprint per year.
AGU’s 62,000-square-foot headquarters currently has a EUI of 90. A net zero building would have a EUI equal to or less than zero. To meet our net zero energy goal, we will need to employ a combination of engineering principles in the renovation to conserve and generate enough power to meet the building’s demands. Roger Frechette, managing principal at Interface Engineering, divides these principles into four categories: reduction, reclamation, absorption, and generation.
The project team first looked at ways to push the building’s footprint as low as possible by reducing its overall initial energy demand by creating a high-performing building envelope (or façade), enhancing the use of natural daylight, and replacing building control systems with energy efficient ones. In addition to improved roof and wall insulation, the exterior design will include new low-e, low reflective glass windows—window technology that reflects heat helping to keep the interior of the building cool. Indoors, a radiant cooling ceiling system, low energy LED lighting system, and a direct current electrified grid, among other strategies, will all help reduce the building’s need for energy.
The next step is to evaluate strategies that will allow the building to reclaim energy once it has been added to the building by reusing it over and over again. Two such strategies would include reusing air and water. Typically, buildings are ventilated with air sourced from outside and must be heated in the winter and cooled in the summer, which can represent more than 30 percent of the energy consumed by a building. By installing a green wall, indoor air that is already at the right temperature will be circulated through the plants where it will be cleaned and filtered of carbon dioxide before passing back into the building, providing a large energy cost savings. A water reclamation cistern on the roof will also be an effective way to reduce water and sewer utility bills by reusing rainwater before it is discharged to the combined storm and sanitary sewer system. The project team anticipates this strategy alone will allow the building to produce all the water needed for flushing toilets and on-site irrigation each year.
Similar to reclamation, absorption strategies look at ways for the building to absorb energy from surrounding resources. The main—and unique—absorption strategy being considered for the building will use energy from the city’s wastewater through a municipal sewer heat exchange system. Close beneath the street on Florida Avenue runs a large sanitary sewer line built in the 1890s. The municipal sewer heat exchange system will tap into the sewer line and divert the wastewater to a settling tank located outside of the building. Water from settling tank will then be circulated inside the building to an exchange system that will extract energy from the water which will be used for both heating and cooling before it is returned to the sanitary sewer system.
By combining the first three strategies—reduction, reclamation, and absorption—engineers were able to reduce the building’s energy use to an EUI of 18. The final piece of the puzzle for the project team to solve was a strategy for the building to generate enough energy to reach the final goal of net zero energy. Vertical wind turbines and solar concentrators were ruled out as viable solutions due to the amount and speed of wind sustained at the building’s location downtown as well as overall cost to develop a custom build solar concentrator. This led to the design of current 11-foot-6-inch high solar photovoltaic (PV) array, which would need to have approximately 660, 360 watt 4-by-8 solar panels to generate enough energy.