The school is green on many levels. It makes use of a “constructed wetland”, which keeps organic nutrients and water on the campus. This maintains a natural wetland habitat, rather than dumping the nutrient-filled water into the Potomac River where they would be wasted. The wetland, Wood says, “demonstrates for our students nutrient cycles, namely nitrogen and phosphorus, and shows them why it makes ecological sense to put human waste to use in the ecosytem rather than simply throwing it away.”
The constructed wetland works by having waste water flow first through a septic tank, not through the city sewage system, to remove solids. It then pumped to the terraced wetland, where it gets filtered by the soil and plants (wetland plant species such as cattails, turtleheads and swamp milkweed). Once the water goes to the basement, it passes through a trickle filter where the water is treated with aerobic bacteria. It is next zapped by ultraviolet light and recycled back into the toilets.
The cooling tower is just one example of this creativity. Located on the roof, the cooling tower is a device that removes warm air. At Sidwell, Wood says there are chillers (machines that cool the water) in the basement of the building that send the water throughout the campus. The water heats up as it moves around. In order to cool it down, it’s more energy efficient to pump the water up to the roof to the cooling tower, which is essentially a big box, says Wood. The water then drips down and cools, a process known as evaporative drip cooling. It is then recycled back into the chillers.
Natural light and air are always preferable, says Wood, and the school makes optimal use of daylight in all classrooms. The science building’s all-glass hallway provides spectacular natural light, but the heat would blast anyone walking through. So the heat is reduced by double-paned windows that contain argon gas between the panes and an outer surface that has a glaze that reflects heat but lets light in. In addition, the installation of light shelves, mounted on both the outside and inside of the building, help shade the sun from directly hitting people in the eyes, says Wood. The light shelves redirect the sun’s rays, bouncing visible light up towards the ceiling which then reflects downward and deeper into the building’s classrooms.
“We want the light,” says Wood, “but we want it to be indirect, and we don’t want the glowing orb that is the sun, blasting us directly.”