Powell Elementary School won the AIA DC Design Excellence and Sustainability awards by telling students to “Abre Las Ventanas” (open the windows). Our renovation and addition to this dual language school showcases solar chimneys and operable windows as passive design strategies. To make the learning environment more comfortable and energy efficient, passive design harnesses the powerful effects of nature… forces like hot air rises and nature abhors a vacuum.
Solar chimneys utilize the natural flows of air current to provide non-mechanical cooling + ventilation. They’re something we don’t see every day, but the concept has been around forever. In fact, the original historic structure included a solar chimney when it was constructed in 1929. This was a time before the use of mechanical air conditioning… a time almost forgotten when schools had operable windows.
We discovered something fascinating when we surveyed the historic building: every classroom had an odd metal grille on the corridor side wall. Each one connected to a duct in the hollow wall that led to the open attic. In spring or fall, when a room got too hot, these vents moved hot stale air out of the classroom and into the attic plenum as students opened the windows. Hot air rises – nature abhors a vacuum. Open a window to let in fresh air: free cooling and ventilation.
So how do you get all that hot stale air out of the attic? The cupola was not just for looks - it functioned as a vent for the attic. Louvers let the hot air out and windows use the sun to heat the space up and speed up the process somewhat.
For the new classroom wing at Powell, we took a lesson from history – we replicated this function and modified it to improve efficiency. Now each classroom has a duct to a solar chimney. When conditions are right - temperature, wind speed + direction, humidity – a green light goes on in the classroom telling the students “Abre las ventanas”. In this day + age we have to encourage our kids to open a window.
The natural ventilation provided by the Solar Chimneys in the addition results in an additional 5.2% savings on energy above the already high baseline for a LEED-S Gold school. The passive strategies in this one wing alone provide cost savings of 2% to the overall project. The solar chimneys provide cool fresh air without the use of non-renewable energy. It’s a concept that is thousands of years old and it’s chock full of STEAM (Science, Technology, Engineering, Art, + Music) teaching moments.
That’s why the folks at DC Sustainable Energy Utility gave us funding for signage in the hallways to educate students on how they work. The STEAM message is levelled for different age groups. It helps explain the concept by comparing it to a fire place chimney within their own homes. However, rather than exhausting smoke, the solar chimney exhausts hot, stale air. It’s a timeless lesson in saving money and energy, promoting healthy buildings, and educating all ages on resource stewardship.
 Nature abhors a vaccum (horror vacui); this idiom and theory by Aristotle posits that empty space does not want to be empty space. When it comes to passive design, this theory is applied in a myriad of ways. Powell Elementary uses the solar chimney and operable windows to create a vacuum. As temperatures warm throughout the year, the vents at the top of the solar chimney can be opened to release the hot air. As the hot air is removed, the empty space left wants to be filled. When used in combination with the operable windows, new fresh air is pulled in to fill the space creating a naturally occurring and desirable draft.