Zero Net Energy Without Adding Zeroes to Cost

This was authored by Jim Moses and originally posted on 21 March 2015.

A Zero Net Energy (ZNE) academic lab-science building is without precedent in the Northeast, but in 2016 Bristol Community College will lead the way in achieving this feat with the completed construction of its John J. Sbrega Health and Science Building, designed by Sasaki Associates. Achieving ZNE means the amount of energy required annually to operate the building will be offset by an equal amount of energy generated onsite. This is no easy accomplishment in a cold climate like Fall River, Massachusetts, where Bristol's campus is situated, but Bristol is a school uniquely dedicated to achieving ZNE.

Bristol has committed to reaching carbon neutrality on its entire campus by 2050. The school drafted a climate action plan* and is making aggressive moves to realize it. With ambitious goals in sight, Bristol and the Sasaki team, which included BR+A and Haley & Aldrich, raised the stakes on the sustainable design of the Sbrega Health and Science Building project, aspiring to make the new building not only an elegant and inviting design, but also a showcase of sustainable building on cold-climate campuses. The building will surpass the state-mandated minimum LEED® Silver certification, which has been required for new construction and major renovations of state-owned buildings since 2007.

In the design and construction of the Sbrega Health and Science Building, the team systematically uncovered ways to eliminate the use of fossil fuels, increase efficiency, and dramatically reduce demand—three critical components of ZNE design—while managing to adhere to a budget which had been confirmed and justified to the state legislature in a pre-design feasibility study. 

Eliminating the Use of Fossil Fuels
The design team set out to eliminate the use of fossil fuels for heating and hot water by implementing two strategies: a dual source heat pump for air and ground and a solar-powered hot water system. The heat pump design allows for a wider ground-temperature range, yielding a reduction in the number of wells. By coupling the system with an air source component, it allows for seasonal optimization, using air in the more temperate shoulder seasons and summer.

The second component of the ZNE design was the ability to tap into the site-scaled 3.2 megawatt solar array** that had been constructed as a separate project. As a standard high-performance design, the building would have used half the power produced by the array, but the more stringent ZNE design uses only about 17%. The building itself also has its own rooftop PV array that helps offset some of the power usage, although the rooftop array alone is not of sufficient size to power the building.

Reducing Demand
Finally, the design team's hunch was that energy demand was driven largely by the 18 fume hoods in the building, designed to exhaust 100% outside air, recirculating nothing. The team recognized the necessity of fume hoods for user safety, and found a viable solution in filtration fume hoods. After much research, discussion, deliberation, and ultimately, the integration of 24/7 air-quality monitoring, Bristol agreed to adopt this relatively new technology. In so doing, Bristol was able to achieve several other energy conservation measures and reductions in first costs, capturing dramatic cost-savings and making adoption of the ZNE approach feasible in the eyes of both the college and the state.

Among the energy conservation measures that followed from this one decision were the following:

•    67% reduction in hourly air changes
•    enthalpy wheel heat recovery
•    decoupling of cooling/heating from ventilation, using fan coil units for local cooling based on space occupancy
•    67% reduction in air handling capacity

A number of significant capital cost reductions followed:

•    reduction of the lab exhaust system, including associated stainless steel ductwork
•    reduction in supply ductwork
•    reduction in air handling equipment quantity and size
•    reduction in floor-to-floor height
•    reduction in building envelope area

Additional Strategies
The team also employed a number of passive strategies to capture still greater energy and cost savings, including the following:

•    implementation of a high-performance envelope by increasing r-value and decreasing thermal bridging and air leakage
•    expansion of the interior temperature range to 70-76 degrees
•    leveraging of natural ventilation
•    reduction in glass use, achieving a 22% window-to-wall ratio
•    self-shading
•    50% reduction in lighting power density

The Reasonable Approach
The great success of this pioneering project is twofold. It is an achievement in design ingenuity, stakeholder alignment, and technological execution, certainly. However, one of its most valuable attributes is its net zero budget execution—a result of taking a holistic approach, rather than simply putting together an unrelated menu of sustainable measures. 

In an environment of great fiscal constraint across the education sector and growing pressures to reach higher benchmarks of sustainability, navigating seemingly competing forces is the linchpin of success. The team invested in early side-by-side cost comparisons during the schematic design phase. Analyzing both a standard, high-performance LEED Silver building and the ZNE approach outline above, the team demonstrated the ZNE building could be constructed without increasing the budget. This delivery of a leading-edge ZNE building should be a game changer for Sasaki's future work across industries. In a world where effects of climate change are manifesting and all resources—including dollars—are limited, this seems the most reasonable approach.

*Bristol is a founding signatory of the American College and University Presidents' Climate Commitment (ACUPCC).

**The college built the array as part of a power purchase agreement (PPA) with a provider, wh0 paid for its construction. As part of the agreement, the college will pay a fixed rate for power for 20 years. After that term, the college may elect to purchase the array or have it removed and the site restored. In order to consider the building as ZNE, the college will need to buy back renewable energy credits (RECs) on the open market for the power generated onsite.