EVERGREEN UNITED
SUSTAINABILITY
ARRAY
GEOTHERMAL
NATIVE
LANDSCAPING
SOLAR
A SUSTAINABLE LEARNING SPACE
One of the main focuses for Evergreen United was to design a sustainable, efficient, and comfortable learning environment that encourages environmental health and development. The team was challenged by the project owners to design and construct a modern, fully net zero carbon high school campus with a minimum of LEED Gold certification as outlined by the U.S. Green Building Council. Many of the early challenges were to gain insight into how net zero carbon performance is developed and how its application in the design process influences cost, feasibility, structural design, architecture, and building technology. Environmental software like SimaPro as well as collaboration between construction, structural, and sustainability teams, helped to achieve a design that accomplishes the owner’s constraint of net zero carbon and LEED Gold certification.
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These goals were critical in designing, constructing, and establishing a sustainable and healthy space for students of the next generation to learn, work, and create. The design teams aimed to make Rachel Carson High School an example of environmentally friendly buildings that make up the next innovation in modern infrastructure.
Why Net Zero Carbon, and How Is It Achieved?
The challenge of designing a net zero carbon educational facility on a large scale was an exciting opportunity to be able to gain exposure to a new future for modern infrastructure. The initial challenge was to connect the conceptual methods of net zero with the design and put them into practice. Once the application of net zero carbon design was further researched, it allowed all teams to point their efforts to a common goal. The U.S. Green Building Council, or USGBC, outlines a general roadmap to achieve net zero carbon performance in a given project. It states that a given building, no matter the location or size, always emits a certain amount of carbon dioxide into the atmosphere. These emissions, in any case, are released by the building’s materials. This includes, but is not limited to structural components, insulation, architectural elements, paints, and finishes.
In order for these emissions to be completely offset throughout the building’s life cycle, renewable energy must be produced on-site. This production must exceed the amount of energy used by the building from the power grid. It is estimated that the process of extracting power directly from the grid emits about 0.14 kg of equivalent carbon dioxide emissions per 1 MJ into the atmosphere each year. The excess of energy produced from on-site systems such as solar panels, represents the amount of MJ of power usage from the grid that has been avoided.
As shown above, the avoidance of power grid usage also results in the avoidance of a certain amount of equivalent carbon dioxide emissions. This amount of carbon dioxide avoided is then used to offset the emissions from the building’s materials assumed earlier, resulting in complete net zero carbon performance.
The application and focus towards net zero carbon buildings is critical in innovating the environmental capabilities of the built world, and greatly reducing the harmful atmospheric impact that buildings can introduce. The development of net zero carbon buildings can greatly influence the health of the planet and future generations.
Life Cycle Assessment Using SimaPro
In order to achieve the process of net zero carbon performance, material emissions as well as power consumption had to be actualized and determined for the specifications of this project. A life cycle analysis software called SimaPro was used to determine the overall environmental impact of the building and its systems throughout its life cycle. SimaPro is a powerful program that provides environmental data for thousands of materials and processes. The latest data model called the ReCiPe Method was utilized to gather values for categories like carbon emissions, ecosystem impact, and resource scarcity.
ReCiPe Impact Categories
The LCA report outlines six critical goals that were used as a basis for achieving net zero carbon performance using data from SimaPro as well as material quantities determined by the construction and structural teams:
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Provide a comprehensive inventory of materials and energy systems used in operation
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Analyze material alternatives and obtain carbon emissions data to assist in sustainable material selection.
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Provide results from a whole-building life cycle assessment, including impact on human health and surrounding ecosystems.
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Using data and results from the life cycle assessment, accurately conclude and outline the net environmental impact produced by the proposed facilities.
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Ensure all building systems produce more energy than they consume, yielding a “net-negative” energy consumption.
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Calculate carbon avoided from energy production, then compare and offset with carbon emissions from materials
Goals #1, 2, and 5 were the most critical to meet not only from a sustainability perspective, but also from a structural and cost point of view. While it was critical to ensure maximum carbon savings, it was equally important to provide a swift and detailed material selection in order for the structural team to conduct appropriate calculations in an efficient manner.
General Structural Material Inventory
Structural Material Emissions Comparison
A general inventory of structural materials with estimated quantities was generated and a preliminary emissions analysis was conducted in order to compare global warming impacts of each material. This analysis assisted in finalizing a mass timber structural frame due to its significantly lower annual emissions compared to concrete or steel. In addition, SimaPro revealed timber's carbon absorption, or uptake, abilities that offset carbon emissions from materials even further. Since wood is a natural material, it is capable of absorbing concrete from the atmosphere; a characteristic that is almost non-existent in a manufactured material like concrete.
Along with carbon emissions and uptake from materials, emissions from energy systems and processes like power grid usage and natural gas were also determined to be compared to carbon avoidance from on-site energy production. Power grid usage on the campus contributed the most emissions out of all energy processees with nearly 12 tons of carbon dioxide being emitted in each year of occupancy. This was consistent to preliminary assumptions made before conducting the LCA. A large solar array consisting of high-efficiency panels were selected for on-site energy production. With nearly 107,000 square feet of panels covering the roof space of the gymnasium and laboratory buildings, about 12.5 million MJ of energy is produced. Since the campus consumes about 12.2 million MJ either from the grid or from natural gas, the on-site energy systems generate a net-negative energy production, which satisfies the offsetting requirements for net zero carbon performance.
Carbon Uptake Values and Carbon Emissions
LEED Scoring and Certification
The project team was tasked by the owners to achieve a minimum of LEED Gold certification for all facilities as outlined by the USGBC. In order to ensure that all aspects of the design and construction closely followed all certification compliancy, comprehensive LEED scoring trackers were constructed for each category. This allowed all team members to monitor and update point totals in real time as the design evolved, as well as accomplish all required pre-requisite credits.
Score Tracking Spreadsheets Used for Transportation and Sustainable Sites Categories
Due to the campus' mass timber construction, large solar array, and heavy implementation of permeable landscaping elements, a large majorty of the points earned came from the "Energy and Atmosphere," "Materials and Resources," and "Sustainable Sites" categories. Before the implementation of the main Alternative Technical Concept (ATC) discussed in the following section, Evergreen United successfully achieved a base certification of LEED Gold.
"Water Efficiency" also contributed a significant amount of points to the overal total. This is due to the on-site, non-potable water system that allows the campus to recycle and reuse greywater to service all three buildings. After research of the surrounding site, it was determined that a water treatment plant in San Joaquin Marsh is located less than a mile east from the proposed campus. The school's water system redirects greywater to the plant where it can be treated. Once processed, the sanitized water is then returned to the campus to be used for building systems like toilet flushing and irrigation.
Alternative Technical Concept (ATC)
Evergreen United was also required by the RFP to create an Alternative Technical Concept, preferably for the energy systems on the campus. ATCs are additional technological innovations or improvements that build upon the baseline building systems in order to achieve more sustainable performance that are proposed to the owner. Since the main focus of the project was to achieve net zero carbon, the largest priority was to implement a system that avoided even further amounts of emissions from energy usage. Nearly 25% of energy usage from large commercial or educational buildings stem from space heating and cooling. This allowed the team to hone in on developing a more sustainble source for internal air conditioning. Geothermal heating and cooling was the most logical and feasible system that can be constructed, and most importantly, maintained on-site.
Geothermal heating and cooling utilizes naturally ocurring heat below the earth's surface to circulate conditioned air throughout the buildings. A deep vertical loop geothermal system was implemented for the campus. A vertical loop system was especially beneficial because of its smaller footprint compared to horizontal systems. The implementation of geothermal heating and cooling results in an extremely powerful combination with the solar array in terms of energy savings, and therefore carbon avoidance. With both geothermal heating and cooling and solar panels, the campus experiences a reduction in overall energy usage of about 72% and carbon reductions from 70% to 100%. This system, in combination with the on-site solar array, yields immense energy, and therefore carbon emissions savings. This results in an overall increase of Rachel Carson High School's LEED certification from Gold to Platinum.
