In June, with a month left in its year-long test period, EcoBuilding Pulse reported that the National Institute of Standards and Technology’s (NIST’s) net-zero-energy house was facing a 154-kWh deficit. In the weeks since, the 2,700-square-foot structure has recouped that loss, and then some, to finish the year with an energy surplus of 491 kWh.
"We made it—and by a convincing margin," Hunter Fanney, a mechanical engineer and project lead, said in a statement released on July 1. "From here on in, our job will be to develop tests and measurements that will help … support the development and adoption of cost-effective, net-zero-energy designs and technologies, construction methods, and building codes."
Located at NIST’s headquarters in Gaithersburg, Md., the all-electric Net-Zero Energy Residential Test Facility (NZERTF) received the U.S. Green Building Council’s LEED for Homes Platinum certification and includes solar-water heating, photovoltaics, and energy-efficient appliances among its green features. Through mechanical controls and digital simulations, the house tracks and responds to the energy consumption of a virtual family of two working parents and two children, ages 8 and 14, while standing up to real weather conditions. To qualify as net-zero, the house must not consume more energy than it produces during a year-long period. The two-story, four-bedroom, three-bathroom NZERTF used 13,086 kWh since the test began a year ago—22% more than projected but half the amount that would have been used by a typical home built to the 2012 International Energy Conservation Code (IECC) standard in Maryland, the NIST team says—for an average energy savings of $364 per month.
Maryland is one of a small contingent of states to have adopted the 2012 version of the IECC. It is joined by Illinois, Iowa, Massachusetts, Rhode Island, Washington, and the District of Columbia.
NZERTF’s energy consumption followed a typical trend, shown in this chart. It registered monthly energy surpluses from July to October. Beginning in November, when space-heating needs increased and the sun’s lower angle reduced the effectiveness of the 32 rooftop solar panels, the home reported monthly deficits. Below-average temperatures and enough snow to cover the solar panels for 38 days also contributed to the loss. But by April, the home was again sending electric power to the grid on most days, NIST says.
The team estimates that adding the required technology and applying energy-efficient construction methods to a similar-scale house built to comply with Maryland’s state building code would add approximately $162,700 to the home’s construction costs.