When Greg Thomas, developer and builder at  Green Key Village in Lady Lake, Fla. set out to build a community of 148 net zero homes, his team was willing to innovate. “We could have done it with typical construction, but our solar arrays would have been at least 30% larger," said Thomas in a recent conversation with BUILDER, "We took the time to ask, ‘How do we bring our energy consumption down so we can get net zero easier?’” To find out, Thomas partnered with software company Ekotrope, which provides a web-based tool to calculate the optimal configuration of a home’s energy components to reduce utility bills and construction costs. Founded in 2010, the inspiration for Ekotrope’s optimization engine grew out of MIT engineering professor Edward F. Crawley’s quest to find the most energy efficient design for his own home with a reasonable payback. Unable to easily analyze component trade-offs to find the best energy and investment combination, his idea was born.

The web-based software runs an advanced algorithm through hundreds of possible energy component configurations. The full version of the software is accredited by RESNET as a HERS and IECC Performance rating tool.

A systems-approach to building design, the web-based interface presents the optimal configuration of a home's energy components to reduce both out-of-pocket costs and future utility bills — hitting the energy investment sweet spot.


Ekotrope evaluates the home as a complete package, says Thomas. Using the Ekotrope interface, he was able experiment with scenarios for the major building systems. For the wall assembly alone, the algorithm ran through frame walls, masonry walls, and ICF walls, then presented how to arrive at different payback times using the different components. The end result was 2x4 framed walls with 3-inches of open cell foam.

Smaller lessons were also gleaned. An 18 SEER air conditioner with a 30-year payback was downgraded in favor of a right-sized model that would match the needs of a tighter system. “We brought our air conditioning needs down, almost by half,” says Thomas. “In most homes here in Florida, the attics will reach 130-140 degree temperatures during the summer. Our duct-work being inside the conditioned space helped us bring the load down.”

Ekotrope updates material costs periodically, but also enables builders to input local prices. “It took a while to get that first house figured out,” admits Thomas. “The hardest part was getting true numbers for the different components. I’ve done this for 30 years, and I know my subs. I know how to get prices out of them. It’s tiring, but in the longer run it pays off.”

Now, each time a new site-plan is submitted, Ekotrope calculates the HERS score as well as the amount of solar power needed to reach net zero energy. “That’s probably where they’re saving us the most money right now, not having to guess. Otherwise, if we guess low we have to go back and put more panels on. If we guess high we’re wasting money.”

The interface also presents an adjustable payback chart that shows the total amount homeowners will save in utility bills over time. Thomas displays this last interface in his design center. Illustrating the hard savings is a strong selling point, he says.

Adjustable Payback and Lifetime Savings Interface via Ekotrope


The Ekotrope interface was made to be tinkered with. “When we have a new idea, we throw it back to [Ekotrope] and they can give us an answer pretty quick as whether it’s cost-effective,” says Thomas, who recently considered swapping out a Solar PV product.

Free online calculators provide a quick way of comparing different combinations of materials for a home’s roof, floor, or wall-assembly, as well as an opportunity to familiarize builders with the Ekotrope model. Learn more at www.ekotrope.com.

Learn more about markets featured in this article: Orlando, FL.