Integrating Sustainable Thinking Into Conceptual Design
Even in cooler climates, net-zero energy is possible
By Nancy Blankfard and Glenn Waguespack
Located on a 160-acre site of forest, marsh, and restored prairie in St. Louis Park, Minn., the new Westwood Hills Nature Center, designed by HGA, includes indoor and outdoor spaces and programming for all ages and abilities.
Photo: Peter J. Sieger
Supporting the city’s Green Building Policy and Climate Action Plan, the zero-energy building serves as a teaching tool, demonstrating passive and active strategies for energy efficiency and stormwater management, while showcasing interpretive exhibits that highlight Minnesota’s landscape and wildlife habitat.
The nature center is a hidden gem within the city, part of a reclaimed landscape—a former golf course purchased in the middle of the last century for public recreation, then cultivated into a nature center with landscape features found throughout the state.
The 13,000-square-foot center replaces a small building from the 1980s. The center will be one of the first net-zero energy buildings in the state—certified by the International Living Future Institute—demonstrating that this type of design is possible, even in cold Minnesota winters.
The center includes multipurpose rooms for environmental learning and public events, outdoor classroom space, public exhibits, staff offices, support spaces, outdoor raptor mews, and parking.
The exposed, all-wood structure of Alaskan Yellow Cedar glue-laminated columns and beams and laminated wood deck embody, on a larger scale, the microscopic structure of bundled parallel cellulose fibers of wood. The exterior skin is expressed in bark-like layers of siding textures and colors. Façades of fiber cement panels and wood window assemblies subdivide and branch out to abstractly represent the geometry of leaf veins, branches, and trunks found throughout the terrain.
The experience of moving through the landscape forms a conceptual framework for the building design. Inside and out, every component becomes an expressive learning opportunity.
Design And Function For Education
The building is located as a gateway to the site, both physically—two trailheads begin/end there—and intellectually through its exhibits and expressive sustainability features. It sits between two native landscape types—prairie grassland and deciduous forest.
Because of the nature of the site, stormwater-management features became critical design tools to integrate the building into the landscape and to educate visitors. Sited near the marshy wetland of Westwood Lake, the building captures roof rainwater to minimize impact on the watershed. The captured rainwater feeds an underground storage pipe and is then pumped, via solar and hand-powered pumps, through a series of infiltration basins to form an interpretive feature that demonstrates the area hydrology.
The energy use of the building is continually on display through an interactive dashboard that connects people to nature. Thirteen didactic placards are placed throughout the center and the grounds to highlight the environmentally conscious strategies, helping educate the public on sustainable design.
Designing For Energy
The design team used several analytical tools to establish strategies and test efficiency through the process, including solar-radiation analysis, wind direction, and daylighting/glare analysis. An energy model was regularly updated as the design evolved, and all disciplines collaborated to fine tune the thermal envelope and building loads along the way to ensure that performance would be achieved as economically as possible. Once the building envelope and systems were finalized, a Life Cycle Cost Analysis demonstrated that the design would save $320,000 in today’s dollars over an equivalent non-net zero building over its 60-year lifespan.
Resilience And Future Climate Predictions
The use of future weather data played a key role in verifying the performance of building systems. The team and owner representatives held a resilience workshop to assess potential risks to the project over its lifespan, everything from public-safety scenarios to the impact of climate change. From an energy standpoint, the team used multiple WeatherShift data sets in its energy model to compare system performance. This was done using projected climate and global-warming scenarios from best case to worst case, ensuring system performance and net-zero energy use over the building’s lifespan. Minnesota’s cold climate is projected to warm, so heating loads will be reduced and cooling loads will increase; data indicate a predicted decrease in overall energy use because the region building-energy use is heating dominant. Therefore, the zero-energy goal remains achievable over the building’s lifespan.
Passive And Active Strategies For Sustainability
From an architectural standpoint, the building shape, form, and materials reflect the goal of integrating sustainable thinking into the conceptual design. The building is oriented to take advantage of solar angles and prevailing winds; its roof form opens the building up to views and maximizes daylight to reduce energy use. From a systems standpoint, the biggest contributor to energy reduction is the geothermal wellfield, which uses the earth as a heat source for the radiant and forced-air systems; heating loads are dominant in a cold Minnesota climate. Beyond that, lighting controls and a building automation system help the facility operator manage the building systems efficiently.
Wood was selected as a structural material for both its warmth and a tie to the surrounding landscape, but also for its low embodied energy. The structure is made of glue-laminated members, which are built of smaller dimensional lumber pieces and can be sustainably harvested. The wood in the building is Sustainable Forestry Initiative (SFI)-certified. The center also has a 150 kW solar array on the roof, comprised of approximately 330 panels.
Design Sensitive To Habitat
Bird-friendly glass is used in a couple of ways. In the exhibit area, large areas of glass from head height down to the floor appear to be clear but are treated with a UV-reflective coating that birds can see because of different wavelengths of light. What birds see is a web of linework, so they don’t fly into the glass. Above these windows, and in other locations, a ceramic frit pattern of horizontal lines spaced 2 inches apart is used to keep birds from striking the glass. The HGA team did a lot of research—bird-friendly glass and testing is an evolving arena—and worked closely with Pella windows to customize the glass for bird safety.
The custom-formed, thermal-feature walls in the main corridor stretch east to west across most of the building’s length. Exterior overhangs and windows are “tuned” so the concrete feature walls will be in the sun during the winter months, capturing heat for thermal comfort. In the summer, the overhangs shade the corridor, so the concrete is absorbing heat from visitors and keeping them cooler. The walls are functional pieces but also express the textures of the birch trees found around the nature center.
Designing For A Positive Future
Designing for nature means thinking holistically about architecture—considering the design and engineering facets but also how architecture addresses equity, accessibility, health and wellness, and climate. How do we maximize a positive impact on people, and how do we think about the building’s future, so its impact remains positive throughout its lifespan? We are at a critical juncture where we can choose to use new lenses with which to analyze and approach design.
Photo: HGA
Collaboration with the city and all partners involved, including RJM Construction, was key to meeting energy goals. The zero-energy goal was the primary challenge—it meant leading from an energy-efficiency standpoint, and all disciplines needed to be creative to develop economical, energy-efficiency strategies. HGA targeted energy budgets early with RJM and balanced energy performance with aesthetics.
Cindy Walsh, Operations and Recreation Director, says, “The city of St. Louis Park is very pleased with the design and management of the Westwood Hills Nature Center project. All of the sustainability components will be used as teaching tools, and we are excited to have this amazing facility in our city!”
Nancy Blankfard, AIA, LEED AP BD+C, is a Principal with HGA in Minneapolis, Minn. Reach her at NBlankfard@hga.com.
Glenn Waguespack, AIA, is a Senior Project Designer with HGA in Minneapolis, Minn. Reach him at GWaguespack@hga.com.
About HGA
HGA is a national, multidisciplinary design firm rooted in architecture and engineering. Founded in 1953,the firm believes that enduring, impactful design results from deep insight into the people and passions that animate each unique environment. Our 11 offices, from coast to coast, craft specialized teams to serve clients in healthcare education, arts, corporate, government, community, and energy industries. Visit HGA.com or follow us on Facebook, Twitter, LinkedIn and Instagram.