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They were two winningly sustainable houses, designed at Harvard to use little or no energy.

A presentation at the Harvard Graduate School of Design (GSD) celebrated this pair of prize-winning student designs: one in France (wholly a computer simulation, created in pixels) and the other in Japan (wholly real, made of native timber).

The setting was “Innovate,” a periodic series of noontime presentations, this one moderated last Thursday by Inaki Abalos, who chairs GSD’s Department of Architecture.

Zero-House was the simulation, created on a computer in stages, from design, to analysis, to redesign, to re-analysis, until it had theoretically met the challenge to transform a commonplace two-story suburban house in eastern France so that it created more electricity than it used, becoming what experts call a “surplus-energy house.”

“One small step was made at a time, and then evaluated,” read the student briefing paper on Zero-House, which noted the “swift, but accurate, feedback” that computer simulation afforded.

The student team of Apoorv Goyal, Keojin Jin, Saurabh Shrestha, and Arta Yazdanseta are master of design studies (M.Des.) students set to graduate in May. They worked with adviser Holly Samuelson, D.Des. ’13, an assistant professor of architecture at GSD who, among other things, studies the energy performance of buildings. Assisting her was D.Des.S. candidate Diego Ibarra.

The biennial competition they won, sponsored by the International Building Performance Simulation Association, typically attracts many more students from engineering than from architecture. To win a contest usually skewed to installing hardware, the GSD team “did what architects do best,” wrote Samuelson in an email. They redefined the problem and “refused to dive into designing complex energy systems.”

Instead, the team combined energy-saving strategies to improve heating and cooling, in search of the right design synergies. They deployed virtual solar panels at the optimum roof pitch, double-glazed windows, improved circulation, installed a heat-trapping berm, and added a Trombe wall, a passive solar use that employs a glass wall to capture and reradiate warmth from wintertime sun.

In the end, the redesigned structure was projected to use 75 percent less energy than the base model provided by the contest rules. Its solar systems also created twice the energy needed for comfort.

The Zero-House team left no footprint on the landscape, but it provided an example of the power of computer simulation to assess strategies for reducing energy use in future houses.

Using virtual models for each step of the energy-saving process allowed for exhaustive cross-checking of strategies, said team member Arta Yazdanseta. It also allowed the team to stretch the bounds of what had been done before. “We needed to break the rules,” she said, “just enough.”