Kroon Hall, Yale University
Vaulted Roof, Ambitious Goals: Yale transforms the site of a defunct powerplant into a low-carbon home for its School of Forestry and Environmental Studies.
With its rustic stone facades and vaulted roof supported by glue-laminated beams, Kroon Hall, the new home for Yale University’s School of Forestry and Environmental Studies, looks a bit like an elegant rendition of a New England barn. But the reference wasn’t intentional, insist its architects, London-based Hopkins with the Connecticut firm Centerbrook. Instead, they say, Kroon’s cladding and roof form are an interpretation of the campus’s gabled stone buildings, while its thin profile and east-west orientation are the result of efforts to minimize heat gain and maximize reliance on the sun for daylighting and energy generation.
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But orientation and configuration are just the most fundamental of a host of tightly integrated features that make Kroon Yale’s greenest facility to date. Taking into account on-site renewable energy generation, the 67,000-square-foot academic building is projected to consume 58 percent less energy than a code-compliant building of similar size and use, according to its project team. The addition of purchased green power allows Kroon, which opened this past spring, to claim carbon-neutral status. The building is on track to become Yale’s second LEED Platinum project, following completion of a studio facility for the graduate sculpture program two years ago. Ambitious construction projects like these, along with campus-wide conservation efforts and renewable energy initiatives, will be key to helping the university meet its goal to reduce greenhouse-gas emissions 10 percent below 1990 levels by 2020.
Kroon is organized around a slot-like stair that cuts through a narrow, skylit atrium, and provides a route from a lower- level library and learning center through two levels of offices to more social functions on the top floor. Here, under the vaulted roof are classrooms and a cafe between an auditorium at one end and an environmental center at the other. This center functions like a “big living room,” says Mark Simon, FAIA, a Centerbrook partner. Sun filters in through the glazed and louvered eastern facade as students study in groups around tables or sit in overstuffed chairs with their laptops.
To achieve Kroon’s high level of performance, the project team didn’t rely on any one strategy or technology. “We took a multi-headed approach,” says Mike Taylor, a Hopkins director. In addition to optimizing its solar orientation, Kroon’s basic scheme includes a highly insulated envelope, a concrete structure largely exposed on the interior to take advantage of its thermal mass and a raised-floor ventilation system, says Paul Stoller, a director in the New York City office of Atelier Ten, the project’s environmental consultant.
Interior climate control is provided via super-efficient air-handling units that recover heat from exhaust air in the winter. During the summer, the units spray water on the return air stream, transferring the resulting “coolth” to the incoming air, explains London-based Dave Richards, a director of Arup, which provided multi-disciplinary engineering on the project. Even in New Haven’s humidity, this indirect evaporative cooling allows the introduction of a large volume of outdoor air, ensuring excellent indoor-air quality, but without consuming huge amounts of energy.
On the hottest days of the year, a geothermal heat pump system provides additional cooling. On mild days, Kroon operates in natural ventilation mode, and occupants are prompted to open windows by a color-coded notification system.
A 100-kW rooftop photovoltaic (PV) array is designed to satisfy about 23 percent of Kroon’s annual energy needs. For the remaining site energy needs, about 415,000 kWh per year, the project team evaluated on-site renewable generation options, but found none to be practical within site and budget constraints. For example, enough additional PV capacity to allow the building to operate completely off-the-grid would have required an array the size of a soccer field, says Taylor. The designers also explored adding PVs to the south facade. “But they would have had limited production capacity and would have been challenging to incorporate in an architecturally satisfying way,” says Stoller. The team did decide to include solar-thermal panels in the south elevation to heat the water supplied to sinks and showers, but opted to purchase renewable energy certificates for the rest of the building’s power needs.
The new forestry building isn’t only notable for its energy-saving features. Kroon is also an important component of a masterplan that aims to remake the part of campus known as Science Hill into an area that would be more sustainable and people friendly. The 3-acre plot where Kroon now sits was a prime candidate for such a transformation. The site, bounded by two L-shaped neo-Gothic academic buildings, was home to a long-defunct gas-fired powerplant and oddly shaped leftover lots used for surface parking. The project team forged an inviting series of outdoor spaces from this neglected parcel by inserting the long and thin Kroon between the two older buildings. The new and existing structures define a pair of grassy courtyards, both of which have a visual connection to Sachem’s Wood—a green space to the east of Kroon, where its geothermal wells are buried. The new southern courtyard is essentially a ground-level green roof built atop loading docks and utilities serving Kroon and the entire southwestern corner of Science Hill.
These new green spaces play an integral role in Kroon’s water-conservation and stormwater-mitigation strategies. An underground tank below the service courtyard collects runoff from the southern part of the site and slowly discharges it, lessening the burden on New Haven’s combined sewer system. From the roof and the northern part of the site, a rainwater-harvesting system collects runoff and channels it to a pond at the border between the southern courtyard and Sachem’s Wood. Here, native wetland plants such as cattail, iris, and lotus remove impurities, including nitrogen, phosphates, and particulates, before the water is directed for use either in irrigation or toilet flushing.
The design team estimates that these measures, in combination with water-conserving plumbing fixtures, will result in a 75-percent reduction in potable water use when compared to a standard building, or a savings of about 500,000 gallons per year. The strategies could also have energy-saving implications, especially if they were to proliferate regionally, points out Nicole Holmes, project manager for Boston-based civil engineering firm, Nitsch Engineering. “Municipal treatment and conveyance of potable water requires energy,” she says.
Embodied energy was a consideration in materials selection as well. For example, about half of the interior’s red oak paneling came from very nearby—the university’s own forest in northern Connecticut certified by the Forest Stewardship Council (FSC). The rest came from a variety of sources, all FSC-certified and within 500 miles of the building site.
The designers also considered the life of the building well into the future. For the exterior cladding, they selected sandstone from Ohio because it is more resistant to deterioration than the relatively more local choice, brownstone. But durability wasn’t the only concern—Kroon is also intended to be flexible. One example is its two floors of offices, laid out on a module, to ease later adaptation. Part of being green is anticipating change, says Simon. “Whatever is deemed as immutable now could be useless in 150 years.”
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