Dreaming of Net Zero

By Sean O’Donnell, AIA, LEED AP, and Raj Setty, PE

Imagine the opportunity to dream up the school of the future. How would it address the issues confronting the 21st Century? How would it foster a more individualized education, adapt to the rapid pace of technology, expand the students’ ability to engage the most pressing issues facing their world?

We recently had the opportunity to explore these questions and push the envelope while developing a concept for a 250,000 gsf urban high school. Since buildings are responsible for nearly 50% of our energy consumption, we concluded that the school should be a model of energy efficiency—a place where children engage the intertwined ecological, social, political and economic realities by demonstrating an alternative future where buildings produce and consume the same level of energy, achieving “net zero energy”.

At first we struggled with this idea: Was net zero even feasible? Would current technology allow such a building in an urban context? If so, how would it educate and challenge its users? Conceptually, achieving net zero is simple—reduce energy usage and generate power to provide for the remaining demand–however, practically this is challenging.

To work toward our goal we created a “Net Zero Checklist” that detailed code and ASHRAE 90.1-2007 requirements, and how we would exceed each and achieve Net Zero:

1. Optimizing Daylight
Configuring the building to allow maximum daylight without overheating or creating glare was a primary goal. While challenging on a tight urban site, every possible space, including the circulation, was located to tap glare-free natural light. Within the classrooms, energy consumption from lighting was reduced to .5 to.75 watts/sf, a goal achieved with a generous floor-to-floor height with correspondingly tall windows with sunshades and reflectors, occupancy sensors, and dimmable bi-level switching. In the public spaces, we targeted .25 watts/sf by using daylight, LED lighting, occupancy sensors, and advanced lighting controls synced with building occupancy profiles.

2. Programmatic Configuration and the Building Envelope
We had already planned on creating smaller academies in classroom “neighborhoods” to foster positive interaction among teachers and students, but we found that these smaller 25,000 sf neighborhoods also helped create discrete HVAC zones. In order to reduce energy transfer, we designed the neighborhoods with super-insulated masonry cavity walls achieving R-30 with “punched” windows and planted green roofs achieving R-49.

3. Reducing Electric Lighting and Plug Loads
Net Zero will also require new ways of using and operating the building. For example, the increasing use of technology could counter a reduction in energy consumption. So in lieu of providing a greater number of outlets for more technology, we incorporated central charging stations, powered by an efficient DC voltage power supply utilizing energy from photovoltaic systems. Using DC to power our lighting too, as is the norm on large naval vessels, we would lose less energy in the conversion to AC and back again.

4. Tapping the Earth’s Energy for Heating and Cooling
A large athletic field lies adjacent to the building enabling the design of a ground source heat pump (“geothermal”) system for heating and cooling. Combined with radiant floor heating and energy recovery wheels, this system will provide thermally comfortable learning environments while conserving significant amounts of energy. Moreover, all of the school’s subsystems, such as kitchen equipment, domestic water, dedicated outside air system, and pool equipment, can be tied into the wells.

5. Zoning the Campus According to Cooling Demand
Our design only air conditions some of the campus. The central glass atrium at the heart of the school, is passively heated and cooled through solar gain and stack ventilation when appropriate, forgoing air conditioning entirely. A radiant floor in portions would provide supplemental heating where people may congregate. Adjacent program spaces are separately zoned with air locks onto the atrium, making it an intermediate environment between outside and air-conditioned places. Air conditioning is provided in classrooms, labs, offices and other spaces where the activity requires more consistent temperature-humidity levels.

6. Generating Energy
Having reduced consumption across the board, our energy model still projected a demand for 3 million Kwh/year. To generate power, we created a solar power plant on-site. To generate an average of 15,000 KW/day, we integrated 200-watt photovoltaic panels onto the roof and supplemented this with Stirling power engines with point focus parabolic mirrors. With a Mid-Atlantic climate, the building would draw power from the utility grid during winter months and provide power back to the grid in the balance of the year. With peak power generation occurring over the summer, a smart-tie power meter would allow the electricity meter to spin backward, alleviating the need for power storage on site.

While challenging, an urban net zero high school can be achieved. Realizing this alternative future requires different financial, operational, educational and design perspectives and, perhaps most of all, the collaboration of a diverse group of stakeholders committed to achieving Net Zero.

By Sean O’Donnell, AIA, LEED AP, Principal, Ehrenkrantz Eckstut & Kuhn Architects, and Raj Setty, PE, Principal, Setty & Associates International

Image Credits: Ehrenkrantz Eckstut & Kuhn Architects and Setty & Associates International in association with Moody Nolan

School Planning & Management, October 2010