Yale's Green Ark
On Kroon's north and south sides are large green courtyards that increase the daylight captured by the building and reduce paved surfaces; they are also comfortable spaces to occupy.
Part of the landscape strategy was to increase the density of trees. East of the building is the expanded Sachem's Wood, planted with some 43 species of trees, which introduces the forest back into the city, mediates between people and the built environment, and provides a green buffer between Kroon and its neighbors.
Green Choices in Materials
Building materials and finishes were chosen for their ease of maintenance and durability, and to serve dual purposes. For example, there is an abundance of natural wood throughout the building, which provides visual warmth. In a sterling example of well-sourced material, half of the red-oak paneling was acquired from the sustainably managed Yale-Myers Forest in northern Connecticut, and all the wood except 30 percent of the glu-lam beams is from Forest Stewardship Council-certified sources.
The curved wood beams that support the distinctive roof are exposed so finish materials are unnecessary. The beams are also an aesthetic triumph, giving the interior a muscular energy.
Smooth-finished concrete walls, floors, and ceilings need no upkeep, and lend a sense of visual permanence to the interior spaces (similar to many of Louis Kahn's buildings at Yale).
The light-colored exterior walls, made of Briar Hill Ohio sandstone, pop the building out of the landscape, giving it a crisp contrast to its rather drab brownstone neighbors. The sandstone has been used for years on Yale's old campus; its light color helps to bounce more natural light into the building.
Much thought and effort were devoted to efficient heating and cooling. The major strategies include ground-source energy derived from four 1,500-foot- (460-meter-) deep looped wells that hold a constant-temperature medium — water at 55 to 60 degrees Fahrenheit (12.8 to 15.6 degrees Celsius) — to help reduce heating and cooling loads without boilers, chillers, and cooling towers. Heat pumps extract the water's warmth in the winter, and in the summer the water helps cool the indoor environment.
During the shoulder seasons of fall and spring, operable windows are used to modulate the interior environment. A system of green and red lights throughout the building prompts occupants to open and close windows to optimize ventilation and thermal comfort.
The building uses a plenum floor, elevated above the concrete slab, for displacement ventilation, delivering air through floor ducts, which is then vented through grilles above the doors. This technique may increase comfort by "enveloping" building occupants with conditioned air from below, instead of blowing it at them from above. Low-velocity fans in the basement propel the air. The plenum floor doubles as a wire raceway.
There are several sustainable features found on the roof. Four solar collectors on the south-facing side provide some of the building's water-heating. Also on the south side is a 103-kilowatt photovoltaic (PV) array that supplies about a quarter of the building's electrical needs. At the roof ridge, a skylight with integrated PV cells allows shaded sunlight to flood the building's central staircase.
At the roof edges are gutters, doubling as window shades, that collect rainwater, which is then routed to the pond in the south courtyard. The rainwater is cleansed of oil and other impurities by a variety of plants, then used for landscape irrigation and for toilets. This system is expected to conserve about 400,000 gallons (1.5 million liters) of water a year.
Kroon Hall is expected to use about 25,000 British thermal units of energy per square foot of building per year (270,000 Btu per square meter per year), which is 58 percent below the energy use intensity of a baseline academic building. Kroon is also expected to have carbon dioxide emissions 62 percent below the ASHRAE baseline, and electrical energy use 58 percent below.
Yale estimates that the green premium on the $33.5 million construction cost was about five percent.
It is hard to imagine a work of architecture better wedded to a client. And one can't help but wonder if the arklike shape of Kroon Hall isn't some unintentional but highly appropriate metaphor for a rescue ship and the salvation it offers as the polar ice caps continue to melt.
Michael J. Crosbie is editor-in-chief of Faith & Form, the chair of the University of Hartford’s Department of Architecture, and a contributing editor to ArchitectureWeek. More by Michael J. Crosbie
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