The Sonnentag: Sustainability Leader.

Going the Extra 36 Miles for Geothermal Savings

The star of The Sonnentag’s zero-net-energy show is a geothermal system involving 190 vertical geothermal wells that plunge 500 feet under the complex’s parking lot – a depth roughly equaling the height of a 40-story building.

Tubing inside each well carries fluid (mostly water) down through 100 feet of loose material and then 400 feet of bedrock, tempering it as it flows through the approximately 52-degree bedrock, and then carries it back up a parallel tube to be returned to The Sonnentag’s mechanical room. There, electric heat pumps finish the job of adding heat during the winter or subtracting heat during the summer and circulating the fluid through the HVAC system and then back through the 36 miles of geothermal wells to be tempered again.

Local Off-site Solar Facility to Supply Complex's Electricity

A solar facility under construction just north of Eau Claire will supply all of the facilities’ energy needs – excluding the Mayo Clinic Health System’s Imaging & Sports Medicine Center. The University of Wisconsin-Eau Claire entered into a 25-year agreement for UWEC to receive 2.8 megawatts of the power produced by the new 5-megawatt facility. UWEC’s 56% share of the energy produced by the facility amounts to an approximate annual energy use of 5,600 megawatt hours of clean energy. The Sonnentag achieves zero net energy (ZNE) status by reducing energy use through optimized designs and operations, along with using solar as its power source.

Right-sized HVAC

The geothermal system’s 36 miles of piping in the bedrock under the parking lot uses the nearly constant 52-degree ground temperature as a heat exchanger where the ground operates as a wintertime heat source or summertime heat sink.

Fluid inside the geothermal piping is tempered by the ground and bedrock and then routed inside the building to the mechanical room’s heat recovery chiller, which has multiple modules that can each operate in heating-only mode, cooling-only mode, or energy-exchange mode. The opposite side of the heat recovery chiller contains heating water pipes and chilled water pipes that are each routed throughout the building to air handling units and air terminal devices that provide heating and cooling to each space. The building automation system includes sensors that monitor the heating and cooling demands in various spaces, allowing the heat recovery chiller to enable or disable modules to meet the current heating and cooling demands of the building. An air-cooled chiller and electric boilers are also integrated into the system for peak cooling and heating demands. The system delivers comfort without the waste of excess capacity.

LED Lighting

LED lighting has been implemented throughout the complex. LED is the most efficient of all lighting options, providing 80% to 90% savings compared with incandescent bulbs and even surpassing the less desirable light provided by fluorescent fixtures. Building automation systems provide a high level of electrical systems control. That means sensors will monitor occupancy, daylight, and carbon dioxide in many locations, and this will tell the lighting systems when they can turn off to reduce energy use and increase the lifespan of bulbs.

Water Heating Costs
34% Below Baseline

Water heating costs for The Sonnentag are reduced 34% compared with baseline energy use. The term baseline refers to the amount of energy and water a building would consume if it were designed using conventional practices. Much of The Sonnentag’s water heating cost reduction is attributed to the efficiency of the fixtures that use hot water. Overall water use inside the complex is reduced about 35% from the calculated baseline through the installation of highly efficient Water Sense fixtures, including 1.5 gallons-per-minute (gpm) showerheads and kitchen sinks, 0.35 gpm lavatory faucets, 1.28 gallons-per-flush (gpf) toilets, and 0.125 gpf urinals.

Minimizing Irrigation

Water use outside the complex is reduced even more significantly – 50% from the baseline level. Ayres’ landscape architects designed 5.5 acres of non-irrigated landscape (mostly featuring a native shortgrass prairie seed mix), 1.8 acres of irrigated lawn, and 1.2 acres of irrigated planting beds containing 2,500 native plantings ranging from black-eyed Susans and Indiangrass to red twig dogwood and American linden trees.

Insulated Building Envelope

Ayres took seriously the need to keep the facilities well-insulated from Wisconsin’s 90-degree summer days and 10-below winter nights. Roof and wall insulation and windows go the extra mile to save energy.

• The design implements high-performing insulation and applies it to the maximum thickness before reaching the point of diminishing returns. This includes extensive closed-cell spray foam in the walls and R-40 rigid insulation in the roof, which generally is where the highest heat loss impacts buildings in the Upper Midwest.

• Windows are thermally broken designs, meaning highly conductive window frame materials such as metal are not continuous from the outer frame to the inner frame, but rather are interrupted by a less conductive component such as plastic. Windows also contain two or more panes, and between the panes lies a layer of argon, which is denser than air and conducts less thermal transfer through the window than an air layer would.

• Windows typically range from U-factors of 0.20 (lowest thermal transfer) to 1.20, and the windows chosen for The Sonnentag have a very low 0.29 U-factor. An even more efficient product – a translucent type of panel provided by KalWall – floods the cavernous fieldhouse with diffused sunlight as its ultra-low 0.14 U-factor keeps cold and heat out.

All About Construction Materials

The environmental effects of the production, transport, and installation of construction materials such as concrete, rebar, and structural steel are called embodied carbon. According to a life cycle assessment that was completed for The Sonnentag design, the project achieved carbon footprint reductions well beyond what a normal – or “baseline” – building design would achieve:

• 21% reduction in depletion of nonrenewable energy used in manufacturing and transport.

• 15% cut in acidification from carbon dioxide that readily dissolves into water and damages ecosystems.

• 14% reduction in the formation of tropospheric ozone, also known as summer smog.

• 14% cut in eutrophication involving the release of mineral nutrients that cause certain species to dominate an ecosystem and ultimately choke out other species.

• 11% reduction in global warming potential.

• 11% cut in ozone depletion, which raises the level of harmful solar UV rays reaching the Earth’s surface.

Embodied carbon reductions are documented through third-party-verified environmental product declarations (EPDs) that state in great detail how a certain product’s production methods reduce carbon footprint compared with baseline products. Over 40 building products with EPDs were specified for installation at The Sonnentag.

Steel from Electric Arc Furnaces

A steel plant in neighboring Illinois was chosen to provide rebar, hollow structural steel, and hot-rolled structural steel for The Sonnentag. It uses efficient electric arc furnaces (not coal-fired) and uses 97% recycled content to produce rebar and 58% recycled content for its hollow structural steel.

Concrete with Lower CO2 Emissions

County Materials Corporation concrete masonry units (blocks) for this project contain 40% pre-consumer recycled content and were manufactured just 53 miles from the construction site.

Eau Claire-based American Materials provided low-carbon mix designs for all poured concrete applications at The Sonnentag. This was achieved by using portland-limestone cement and increased fly ash content, both of which reduce the embodied carbon of the material. Concrete production is a major source of carbon dioxide, accounting for an estimated 7% of human-made CO2 emissions worldwide.

The design team worked with American Materials to generate EPDs for its products, and the company can now use those EPDs to market to future customers who are interested in using materials with a reduced carbon footprint. In this way The Sonnentag project has helped contribute to market transformation in this region and supports goals of using The Sonnentag as a sustainability education tool for the larger community.

American Materials was able to demonstrate that all mixes reduced embodied carbon by 12% to 20% compared with the baseline.

Beautiful Impact

Among the most creative and beautiful ways The Sonnentag project reduced the building-material-related carbon footprint is the reuse of old bleachers from UW-Eau Claire’s Zorn Arena – the former venue for basketball games – as a feature wall in the main concessions area. This reduced the need for production and purchase of new wall cladding for this area and provided a respectful nod to the past.

The design team also used wood from trees that were taken down around the UW-Eau Claire campus for a wood wall feature behind the seating along the lobby’s east wall.

Hitting the Mark for Sustainability

Sustainability is a key aspect of UW-Eau Claire’s strategic plan, and students voted in favor of student fees to support the project, including the money needed to seek LEED certification. The main financial push supporting injecting sustainability measures into the design came from the Eau Claire-based Pablo Foundation, which provided nearly $10 million – roughly half in direct philanthropy and half in low-interest loans to be repaid with the facility’s energy savings. The Pablo Foundation money funded the geothermal system, efficient windows, and extra wall and roof insulation. The City of Eau Claire committed $1.5 million to the project’s sustainability features.

What is LEED?

The Sonnentag has been certified LEED Gold v4 BD+C: NC. That stands for “Leadership in Energy and Environmental Design for building design and construction for new construction.” LEED is the world’s most widely used green building rating system, recognizing best-in-class building strategies and practices that save money, consume less energy, and use less water. Preceding the LEED certification is a process of commissioning, during which an independent service verifies that building systems are performing as designed.

In order to be LEED-certified, a building must demonstrate achieving a minimum level of energy efficiency to reduce the environmental and economic harms of excessive energy use. Energy modeling according to ASHRAE Standard 90.1-2010 Appendix G was used to quantify The Sonnentag’s energy efficiency and cost savings against the baseline. The term baseline means the amount of energy and water a building would consume if it were designed using conventional practices.

Following the Appendix G methodology allows for earning credit by exceeding standard practices not regulated by Standard 90.1, such as optimized window area and orientation, selection of more efficient HVAC and service water heating equipment types, right-sizing HVAC equipment, and efficient use of thermal mass, which is a building’s ability to absorb and store heat during the daytime and give off that heat at night.

What is WELL HSR?

The complex has received a WELL Health-Safety Rating certifying the ability of its operations, maintenance, and emergency policies to improve occupants’ health and well-being. Developed by the International WELL Building Institute, a WELL HSR rating means occupants’ health and safety are prioritized in practices including cleaning and sanitization, health services, and air and water quality. HSR programming includes measures such as:

• Devising a business continuity plan that will keep critical business functions going in the event of an emergency such as a blizzard or pandemic.

• Implementing social distancing strategies and increased ventilation during a respiratory health crisis.

• Planning how to guard against the serious pneumonia threat of Legionella bacteria that forms in stagnant water. Such a risk could arise if the facility were mostly shut down during an adverse event.

UWEC’s comprehensive policies for university facility employees’ access to sick leave, vaccinations, and mental health recovery also contribute toward achieving the WELL HSR.

Site Cleanup

The project team completed an extensive site inventory analysis in early conceptual phases of this project. The 2019 inventory analysis reported that the site was originally dedicated to lumbering operations. Most recently the site was home of the County Materials Corporation, an aggregate supplier and manufacturing company. The land had undergone intensive industrial activities over the years and had been classified as a brownfield. Ayres conducted asbestos and lead-based paint assessments and hazardous materials surveys.

Ayres wrote U.S. Environmental Protection Agency (EPA) cleanup grant applications and analyzed brownfield cleanup alternatives for the properties that now comprise The Sonnentag site. Ayres assisted with a successful application for a $500,000 Wisconsin Economic Development Corporation (WEDC) Idle Industrial Site Redevelopment Grant and a $400,000 EPA grant. The funds were used for demolition and remediation.

Concrete from the old buildings on the site was crushed and provided nearly all the base course under The Sonnentag’s paved areas.

More Natural Flora, Less Runoff

The redevelopment of the brownfield site and reintroduction of native plantings and abundant green space has significantly improved the health of the site. Ayres designed 5.5 acres of non-irrigated landscape, mostly featuring a native shortgrass prairie seed mix, and 1.2 acres of irrigated planting beds containing 2,500 native plantings ranging from black-eyed Susans and Indian grass to red twig dogwood and American linden trees.

The site design also removes 80% of suspended solids from stormwater runoff – twice the required level of treatment for the site – to protect the adjacent Chippewa River. The largely permeable condition of The Sonnentag site is in stark contrast to the 100% impermeable (compacted gravel) condition of the site before the project. This allows for more effective groundwater recharge.

Density and Diversity of Surrounding Amenities

Location and transportation are crucial considerations when assessing site selection and its environmental and social impacts. Connecting the site to the existing surrounding recreation areas and ensuring it is physically accessible to the public was a goal of Eau Claire Community Complex, Inc., from project conception.

The project location fit well as a sustainable development because its location near the heart of Eau Claire features direct access to a city bus route and nearby amenities and services, which helps to reduce the need for private vehicle use and promotes a more sustainable lifestyle.

This site also has ready access to numerous diverse services such as civic and community facilities, retail, entertainment, and commercial uses. A hotel has been constructed directly west of the event center, and a waterfront restaurant is planned for the future.

The building site is designed to be used as social and recreational areas. All of the pedestrian paving connects the building to outdoor recreation, including city biking/hiking trails leading east, west, and north; nearby Carson Park with its baseball stadium and football field; and the Chippewa River for tubing, kayaking, and canoeing. The hardscape around the building has seating for eating, studying, or enjoying views of the river and trail system.

EV Charging, Green Vehicle Parking, Bike Racks

Ten Level 2 (mid-speed) electric vehicle charging stations are planned in prime locations in The Sonnentag’s parking lot. Underground conduit and electrical panel circuits also have been installed to make it easy to add up to 20 more charging stations in the future. An additional 25 preferred parking stalls are set aside for green vehicles – a class of cars that includes EVs, hybrids, and a handful of highly efficient internal combustion engine vehicles. Abundant bike racks are conveniently located.