Project Frog is similar to modular home builders like Living Homes, Michelle Kaufmann Designs and Zeta Communities. The difference? It's focusing on commercial buildings rather than residences.

The big question now is whether commercial developers will warm to their pre-fabricated, energy efficient construction modules. This week, the San Francisco-based company raised $8 million in a second round of funding from, among others, Rockport Capital.

Like other green builders, the company plans to produce energy-efficient building modules in a factory, cart them out to a construction site and then bolt them onto the foundation. Building in a factory can save both time and money. Many green building advocates also point out that you can get tighter seals on walls and windows, thereby reducing heating loss.

A substantial portion of the energy savings Project Frog touts comes from the fact that the buildings are designed to exploit the sun for indoor lighting as well as ambient air for cooling. Heating and air conditioning systems actually consume about 15 percent of the total energy in the U.S. a year. In the Pacific Northwest, for instance, many LEED buildings are now being built without air conditioners.

Property developers, however, are very conservative and often reluctant to work with new products, technologies and contractors. To some degree, the caution is understandable. Unlike a laptop, buildings have to last for decades.

Project Frog will initially target schools. It showed off a 1,280 square foot "School of the Future" at Greenbuild earlier this month, a heavily attended conference in Boston. The building consumes 75 percent less energy than a similar, conventional structure. Modules can also be strung together to make a larger structure.

The company will also construct a building at the Watkinson School in New England that should be ready by September 2009.