Sustainability has been an integral component of the project since its inception. Through the feasibility study and design process, and now during construction, sustainability has guided much of the final design.
Sustainability holds such importance for several reasons:
It helps Arlington make significant progress toward its goal of being carbon neutral by 2050, a goal set because of concerns about climate change.
An efficient, sustainable design reduces long-term operating costs for our largest town-owned building.
A building designed with sustainability in mind will create learning opportunities and provide a healthier environment for our students
Achieving a certain level of energy efficiency and sustainable design, as measured by the LEED rating system, qualified the project for an additional 2 percentage points reimbursement from the MSBA (Mass. School Building Authority), or about $3.5 million. The new high school is on track to receive LEED Gold status and the project team is working hard towards a goal of LEED Platinum.
Energy use in the new AHS
The reach goal of creating a net zero energy building guided the Building Committee in formulating approaches to sustainability. Although net zero energy is not currently achievable (because the building will not produce as much energy as it uses), much progress has been made toward important outcomes:
A key metric for energy use is the Energy Use Intensity (EUI), measured in thousands of Btus per square foot per year (kBtu/sqft-yr). A tight building envelope (windows, insulation, etc,) + efficient systems (HVAC) = a low EUI. The current high school has an average EUI of about 66 kBtu/sqft-yr. The most recent energy modeling of the new AHS shows an EUI of 25. Since the total square footage of the current and the new building is about the same, the new building will use less than half of the total site energy as the current building, yet will provide far superior comfort for occupants.
Achieving these results requires not just an efficient base design but also careful consideration of how the building will be operated to minimize energy use while meeting the diverse uses of the high school. The building will use efficient air-source heat pumps (ASHP) as the primary heating and cooling technology. Innovations in heat pump technology are allowing wider application in cold climates, making this a viable option for the high school. Unfortunately, the original plan to use ground-source heat pumps, which are even more efficient, had to be abandoned after a test well showed soil contamination significantly beyond what was expected. Nevertheless, the expected EUI of 25 is an excellent result for a building that is used as much as the high school.
Heat pump technology not only offers the most energy efficient option for heating and cooling, but it is also key to positioning the new AHS to operate free from fossil fuels. By electrifying all end uses, including those traditionally met using natural gas in a building of this type (space heating, hot water, cooking), we can avoid the direct use of fossil fuels.
The new high school’s operational energy will be entirely electric. Even though fossil fuels are used to generate electricity today, as the electricity grid gets cleaner over time, the carbon emissions and other pollution associated with the building’s electricity use will continue to decrease. Massachusetts has a requirement that all electricity sold contain increasing amounts of renewable energy each year, and in its Net Zero Action Plan (February 2021), Arlington set a goal of sourcing 100% renewable electricity by 2030 for all town facilities.
Onsite renewable energy, typically rooftop solar power, helps achieve the project’s climate and energy goals. The existing rooftop photovoltaic (PV) arrays from the current AHS will be relocated to the Phase 1 buildings (the Science, Technology, Engineering, Arts & Mathematics classroom wing and the Performing Arts wing). When completed, the building will have enough roof space to significantly expand the total amount of PV onsite. The design also includes installing a canopy over some of the onsite parking to further increase the amount of solar electricity generated onsite.
Rather than the town investing capital and maintaining the systems, it purchases the power under long-term contract, called a power purchase agreement (PPA), at a rate lower than the retail price of grid-supplied electricity. The town will expand this arrangement with the additional solar generation.
The additional solar generating capacity will be coupled with an onsite battery storage system that will help balance the variable nature of solar electricity production with the electricity load of the building, further reducing the building’s energy costs. The battery can also participate in a utility demand management program designed to provide grid support during periods of systemwide peak demand. This can help avoid power outages and defer the need for additional grid investments, saving all utility customers money. Participation will result in additional savings to the town.
Electric vehicles play a significant part of the Town’s goal to be carbon neutral by 2050. To support this, EV charging stations will be installed in approximately 10% of onsite parking, while the remaining parking will be “EV ready”, with the installation of underground conduit so wiring for additional charging stations can be added easily in the future.
Additional Considerations in Sustainability Efforts
In addition to the major goals listed above, there were several other considerations which affected sustainability work, with both positive and negative impacts.
The building project is participating in the Accelerate Performance Program being offered through Arlington’s two utilities, Eversource and National Grid. The pilot program offered enhanced incentives to adopt aggressive, but realistic, energy use targets early in the design process. The program is specifically designed to incorporate these goals early enough in the design process so that it is possible to achieve the desired energy performance at no or low incremental cost.
Participation provided Arlington with free technical assistance paid for by the utilities (normally this is cost-shared with the customer), and guarantees a minimum level of financial incentives of $0.50 per square foot, or just over $200,000. Actual incentive levels, which are likely to be higher, will be determined once the actual EUI of the new building is determined.
The AHS site is only 22 acres, which is smaller than many high school campuses, and smaller than the minimum recommended by the MSBA. While having a compact building footprint has its advantages from an energy efficiency standpoint, it also means that for the given floorspace of the building, there is relatively less roof space on which to install solar panels (for example, multiple 2 or 3-story classroom wings instead of a single 4 or 5 story wing would have more roof space for the same floorspace). There is also limited onsite parking over which to build canopies for additional PV.
As a result, and despite the low expected EUI of 25 the site will not be able to host sufficient solar generating capacity to achieve the goal of net-zero energy operations.
The AHS Building Committee Sustainability, Mechanical, Electrical & Plumbing (SMEP) Subcommittee was formed at the very beginning of the project. The group set sustainability goals, worked closely with the design team to reach these goals, and continues to monitor progress towards those goals. The subcommittee covers broader “MEP” design issues (mechanical, electrical, plumbing) given the high degree of overlap between MEP considerations and energy use.
The SMEP Subcommittee includes several members of the AHS Building Committee (Ryan Katofsky (Chair), Kate Loosian) HMFH design team, including AKF, which has significant experience with net zero energy buildings. The Town’s Energy Manager, Facilities Director, and APS Sustainability Coordinator are also on the SMEP Subcommittee.
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