Elementary Rules of Rainwater, Daylight and Heat Gain26 Jul, 2006 By: Kenneth Wong
Ushering nature into Ben Franklin Elementary School.
Where do ideas come from? If you ask the principals at Mahlum Architects, they might say, as stated on their Web site, “They stem from a process that’s two-thirds orderly -- sitting in a room away from distraction, thinking -- and one-third pure Aha!” When thinking about designing the Ben Franklin Elementary School in Kirkland, Washington, the "Aha!" was the woods surrounding the site.
“The intent is to connect the school environment to the native environment,” explains David Mount, an associate and project architect at Mahlum. “In the courtyards and around the building, you’re constantly coming in contact with nature. The building’s wings reach into the woods on the site’s north edge and, on the second floor, create a feeling of being up in the trees.”
Because Lake Washington School District, the owner, anticipated local, regional and national mandates for sustainable architecture, all interested parties in the Ben Franklin Elementary School project held an eco-charrette during the planning phase.
“In an eco-charrette, all participants in the project -- architects, landscape architects, engineers, owners, staff and even the community -- work collaboratively to establish sustainability goals,” Mount says. “The collective buy-in ensures that maintenance staff, for example, won’t be surprised by the installation of waterless urinals and their care requirements after the building is complete.” During the eco-charrette, Mount and his colleagues learned about the community’s affection for the woods, their desire for water conservation and the rest of their green concerns.
The design team’s storm water strategy was to collect rainwater from the butterfly roofs and direct them to the bio-retention cells located in the parking islands and other landscaped areas. AIA notes, “The Ben Franklin Elementary School is the first project within the city to utilize this innovative approach.” The school was selected as one of the 2006 Top Ten Green Projects by AIA/COTE (Committee on the Environment).
|The design of Ben Franklin Elementary School by Mahlum Architects incorporates two courtyards, giving children access to miniature ecosystems for exploration and learning (photo courtesy of Benjamin Benschneider).|
Ventilation and Illumination
“People think it’s constantly raining here,” Mount observes. Contrary to the ever-gloomy Seattle depicted in movies such as The Ring or TV series like Twin Peaks, the Pacific Northwest offers," according to Mount, “an abundance of light and air. Windows can be left open for most of the year.”
Budget concerns aside, air conditioning the classrooms would not have met the district’s energy efficiency policy. To that end, even forced ventilation with electric fans must be kept to a minimum. So Mahlum conducted a series of daylighting, airflow and thermal analyses with the help of Stantec, a mechanical engineering consultant firm, and Seattle Daylighting Lab, a daylighting consultant firm.
How Hot Does it Get?
Mount recalls, “We simulated everything: How intense is the heat in the gym? How many kids will typically be inside at a time? What is the heat gain from their activities? What is the heat gain from computers? How about inside the classroom where everyone will be sitting? What is the indoor temperature in relation to outdoor temperature?”
“The thermal analysis application we used (TAS from EDSL or Environmental Design Solutions Ltd.), is similar to a finite-element analysis package,” says Matt Younger, PE, LEED AP, a Stantec principal who served as project lead for the Ben Franklin Elementary School. “It’s used to calculate heat transfer. It also takes into consideration thermal lags [the time delay before reaching maximum or minimum temperature]. So we inputted the building architecture [geometries] and weather conditions. The software helped predict what the expected temperature would be, what the airflow and air patterns would be in occupied spaces, depending on what the weather was and what the occupants would be doing.” Stantec used the outcome of these analyses to determine the size of the ventilation shafts and operable windows and the amount of glazing and assist the architect in designing exterior shading devices for control of heat gain while still allowing daylighting .
According to Younger, at the time of the project, they could not directly import AutoCAD data into the thermal analysis software. “So we basically had to redraw the building geometry in a separate software package,” he recalls.
Technology has made numerous advances since, producing some analysis packages that can generate a 3D model based on an AutoCAD file. IES’s VE, or Virtual Environment, is one of these products. Still, Younger and his colleagues spend many hours inputting building geometries into analysis packages. “If we see that the design doesn’t perform well (in thermal analyses), we’ll try different alternatives, so we have to change the geometries. So being able to blend geometry input and CAD is a great value to us, but there are still complications that arise from layers and blocks.” Younger hopes the technology will eventually allow him to export modified geometries from an analysis package in a format that is readable by standard architectural CAD systems.
Where Does the Light Fall?
Ben Franklin Elementary School’s design team also simulated the affects of different natural light conditions using a physical model made of cardboard and wood. Mount recalls, “We placed the model under a (simulated) overcast sky, as well as under bright daylight... Achieving the right balance of light in each classroom is important, as studies indicate that the glare caused by direct sunlight can negatively impact students’ ability to concentrate.”
|The exterior of Ben Franklin Elementary School (top photo courtesy of Benjamin Benschneider) and the physical model used to conduct the daylighting study (bottom photo courtesy of Daylighting Labs).|
Based on these findings, the design team adjusted the building components to fine-tune the envelope. In places where too much heat gain was anticipated, overhangs and other shading devices were used to diffuse the impact of direct sunlight. In other places, operable window areas were enlarged to provide more airflow to cool the building.
“(Analyses on digital model and physical model) focused on different results,” Mount explains. “The digital model by Stantec does not need to locate the direct sunlight -- rather, it considers the heat gain caused by it.”
“Daylighting and natural ventilation work hand in hand,” says Stantec’s Younger. “A lot of times, we use the cooler nighttime temperature to control the daytime temperature.”
|Schematics showing the results of thermal analyses and daylighting studies (images courtesy of Mahlum Architects).|
The Left Brain vs. the Right Brain
Mount is concerned that because sophisticated CAD packages often require a high degree of software proficiency, over-reliance on these systems may stifle some of his fellow architects’ right-brain thinking -- the side that entertains lofty concepts and inventiveness. Reflecting the firm’s design ideals, Mahlum’s Web site is evenly divided between content for the right brain (intuition) and the left brain (logic) -- the former populated with philosophical musings and quotes, the latter filled with practical information.
One exception from the overly left-brain programs, however, is the low-cost, easy-to-use SketchUp. “We’ve become quite taken with SketchUp,” he says. “We use it to design, make decisions, present ideas. Now we produce many of our 3D models in SketchUp, and then import them into Photoshop for refinement.” Mahlum staff also use Autodesk VIZ to produce presentation-quality renderings of projects.
On paper, Mahlum’s client for the project is Lake Washington School District, but ultimately its clients are the children. What kind of living and learning spaces should an architect create for snacking kindergarteners, dirt-kicking sixth graders and the rest of their cohorts? Instead of resorting to playful gimmicks and schizophrenic color schemes, Mahlum decided on a different approach. “We are advocates of a muted color palette that provides a neutral backdrop for students’ activities and work,” Mount reasons. “It’s about creating a healthy learning environment. We want the kids’ creativity to shine, and the environment to support that.”