Sustainability

 Sustainability Outcomes for New Ellen Garrison Building at the Concord Middle School

Prepared by Charlie Parker and Matt Root1, Concord Middle School Building Committee

April 6th, 2025

At its annual meeting in 2019, the Town of Concord approved funding to proceed with the design of the new Concord Middle School with design stipulation for an energy efficient, all- electric, net zero building. At this point, it’s safe to say that we have met these objectives in an exemplary manner, providing a template as well as ‘lessons-learned’ for future high-efficiency, net zero buildings in Concord.

Our process focused on metrics for efficiency, starting with the recognition that we wanted to build a school that met the highest efficiency standards in Massachusetts for schools while respecting the need for fiscal prudence. Our overarching goal was to meet or exceed the performance of the most sustainable schools in Massachusetts and we settled on an Energy Use Intensity (EUI) goal of 25, based on our committee’s research and on our architect’s recommendations. The EUI is a measurement of the total energy use per square foot over the course of a year and is a roll-up, or summary, of all sources of energy consumption by the building: heating and ventilation, lighting, kitchen, all classroom uses of electricity, domestic hot water, etc. This measurement is a standard which allows for comparison to other schools and is used as the baseline for all engineering and modelling of the building. As such, the EUI is

the North Star for the design of most of the components of the building as the attributes of each element contribute to our energy consumption – floors walls, windows, roof systems, heating and ventilation, and so forth.

From the start, our primary concern was with the design of the building enclosure. Our concern was two-fold. First, as New Englander’s know, a tight building enclosure is more comfortable, regardless of the type of heating system, as drafts and air leakage are minimized. While we did focus on a competitive level of insulation for the roofing and the walls, as well as high performance windows, our primary driver was to achieve an aggressive metric for air

infiltration, as measured by a test of the building’s tightness (using a ‘blower door test’) and we exceeded our infiltration metric with results of 0.11 cubic feet per minute per square foot of enclosure at a pressure of 75 Pascals, which is well below our target metric and significantly

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1 Note about the Authors. Charlie and Matt have been members of the Middle School Building

Committee since its establishment in June, 2019. Both are ‘community volunteers’.

• Charlie is a former Chair of the Concord Sustainability Committee and served as a member of Member of the Solar Implementation Task Force, as well leading on a wide range of energy upgrade projects for Concord’s buildings. Charlie has worked in high- technology for 30+ years.

• Matt Root has been our Chair of the Sustainability Subcommittee for the CMSBC. Matt has worked as a sustainability consultant in the construction industry for over 20 years, with the first part of his career in building performance, and more recently a focus on healthier materials.

below code (goal for building was 0.15 and Massachusetts code specifies 0.35). The detail on this point demonstrates our use of building science metrics and a successful, engineering-based approach to the building. It’s also worth noting that the air infiltration metric is one of the most difficult to meet and indicates high build quality.

Additionally, the committee focused on mitigation of thermal bridging issues to improve the efficiency of the heating and cooling of the building (thermal bridges are construction elements that conduct heat). We focused on the selection of materials that are less susceptible to thermal bridging as well as best practices to minimize this problem. Again, this was part of our strong focus on a high-performance building enclosure to enable us to achieve our EUI.

Heating and cooling are delivered to the various spaces via electric heat pumps located on the roof. And, ventilation is through a completely separate ‘dedicated outdoor air system’ or fresh air system. We paid careful attention to this system to enable the delivery of sufficient fresh air to meet standards for CO2 mitigation in the classrooms. This balance between oxygen and CO2 is automatically controlled by sensors which activate fresh air distribution from the outside as needed to meet the CO2 standard. But, unlike conventional construction which does not provide fully separated air flows (heating/cooling vs fresh air), the fresh air system for CMS uses

100% fresh air rather than mixing the fresh air with existing building air. This allows us to

provide an optimal level of fresh air while retaining the energy that was required to heat the space in the first place. The evidence of benefits is compelling. A study of 100 U.S.

schools found a direct association between student academic achievement and classroom ventilation, where school indoor air quality was improved.2

Out of all design parameters in schools, including air temperature, acoustics, and

CO2 concentration, according to one study, daylight has the highest impact on overall student progress3. Natural light positively contributes to a higher academic performance in reading as well as in science4. It also supports attention, the stability of the circadian cycle and overall health, mental health and comfort, which in turn, leads to better academic performance. Lighting in each of the classrooms was optimized using a daylighting simulation/model to maximize daylighting. By modeling the daylight every learning space, we were able to

maximize daylight for learning space while achieving the sustainability goal objective of 25% for window-to-wall ratio.

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2 U. Haverinen-Shaughnessy, D. J. Moschandreas, R. J. Shaughnessy, Association between substandard classroom ventilation rates and students’ academic achievement, 24 August 2010

3 Barrett P, Davies F, Zhang Y, Barrett L Enviro. The impact of classroom design on pupils’

learning: Results of a holistic multi-level analysis. Build n. 2015

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Otherwise, electric lighting is 100% via LEDs which are 80-90% more efficient than incandescent lighting. As an added sustainability feature, the LEDs are controlled by a lighting management system that measures each lighted area and automatically adjusts the LEDs to an optimal level.

Our financial objective was to achieve our sustainability goals while also demonstrating the financial feasibility of this approach. The question here is whether we can afford to build a low EUI building that’s 100% fossil-free and affordable. The answer appears to be YES on a variety of criteria. First, the incremental cost to build an all-electric/high-performance building is only

1.4% of total building cost over a conventional, natural-gas heated building. For 1.4% incremental cost, we have delivered a building which is more than 2x as efficient as the most recent Concord construction (CCHS). Second, the payback timeframe for the incremental investment over the ‘base case’ is 7.4 years, well within the ‘reasonableness’ guideline. What this means is that the operational savings on building energy consumption is significant enough to pay-off the incremental investment in a relatively short amount of time.5  The significance is that the Town of Concord will realize 100% of the annual operational savings for the life of the building, from the end of the initial 7.4-year payback period for a full 50 or 60 years. And, related to this, we are achieving an annual energy savings of 49% over the state energy building code.

And, finally, we are fully LEED Certifiable. This reflects ratings a wide range of criteria, including healthy building materials, high water efficiency, and variety of outdoor criteria.

Last, but not least, the building and parking areas have been built out as 100% Net Zero Ready to allow the Concord Municipal Light Plan (CMLP) to pursue the development of a Solar Photovoltaic power generating system on the roof of the new CMS and on canopies in the parking areas. If and when this new system becomes a reality, the Solar PV system will generate enough electricity offset 100% of the building’s annual electricity consumption. We

expect the bidding for the PV project to commence in April of this year and for installation to be completed by the end of 2025, if the CMLP is able to pursue this opportunity. Our thanks to the CMLP for their leadership in working with us on the solar ready design aspects and for their willingness to pursue this opportunity. As details on the system are still unfolding, we will keep you posted.

It was a privilege to work with our Hill project management team and with Ewing Cole/SMMA’s architects and engineers through this long and interesting odyssey. At this point, we can agree that we met our objectives and we should all be proud of our sustainability contributions to the Town of Concord and to a comfortable, healthy, and safe new Ellen Garrison Building at the Concord Middle School.

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5 This is based on SMMA’s cost of ownership analysis comparing a base-case equivalent building (minimum code standards) to our high-efficiency building with enhanced HVAC, insulation, windows/fenestration and lighting system. First-cost and operating costs were compared for each scenario to determine the break-even time of 7.4 years for the high-efficiency scenario (our CMS design).

Attachment: Detail on Metrics (From SMMA)

Summary Against Key Metrics for CMS Net Zero Energy Building:

Predicted EUI (100% Construction Documents):                                  25.1 kBtu/SF/yr. 

Estimated Incremental Costs:                                                               1.4%

Estimated Payback for Incremental Investment:     7.4 years

Estimated Annual Energy Savings:                                 49% (exceeds MA Stretch Code/2018 baseline)

Building Enclosure criteria:

• Exterior Wall assemblies:                                           R-30

• Roof:                                                                                 R-46

• Fenestration (glass):                                                   0.23 Assembly U-value (IGU at 0.14) – triple

• Window to Wall Ratio (WWR):                                25%

• Whole Bldg. air infiltration reduction:                   0.11 cfm/SF/yr. [goal: 0.15 cfm/SF/yr]

Other key energy/sustainability attributes

• All-electric heating and cooling heat pump system

• Heat recovery

• 100% Outside Air DOAS ventilation system

• Demand Control Ventilation (CO2 sensors)

• Efficient LED lighting systems and controls

Renewables for NetZero (Solar PV)

• Proposed: 1.2 MW on-site solar PV system with 4 MWhrs battery storage: PV generates estimated annual building electricity consumption.

 (PV project financials are separate from building financials. PV is a CMLP Project).

Meets or Exceeds LEED Certification Requirements

• Water Efficiency:                                                       27.3% (estimated)

• Water Sub-metering

• Rainwater [storm water] management system – reducing peak run-off

• Outdoor classrooms and access to nearby natural wetlands

• Re-use of an existing site

• Heat island reduction with light colored roof and sections of paved areas.

• EV charging stations: 2 dual stations (4 vehicle chargers) installed and 10% readiness.

• Drought resistant landscapes with native and adaptive trees, perennials, and ornamental grasses.

• CO2 sensor set at 800 ppm (Indoor air quality)

• Low-VOC (volatile organic compound) materials for interior materials and coatings

• Formaldehyde-free, low-VOC particleboard and composite wood products

• Maximal use of high recycled content materials and regional

• Operable windows, interior window shades, and individual temperature and lighting controls for each classroom and leaning space allow for flexibility and control of individual thermal comfort.

• Fenestration (window) design optimizing access to views and natural daylight