Researchers at the National Institute of Standards and Technology’s (NIST) Maryland campus recently ended a year of intensive study on a four-bedroom test home that will help builders construct cost-efficient net-zero-energy homes.
Both a laboratory and a house, the Net-Zero Energy Residential Test Facility (NZERTF) is roughly 60 percent more energy efficient than a similar house built to 2012 International Energy Conservation Code requirements. The 2,700-square-foot LEED-Platinum house, built by Therrien Waddell Construction Group, features a well-insulated building shell, energy-efficient appliances, solar water heating, and a solar photovoltaic system.
“The most important difference between this home and a Maryland code-compliant home is the improvement in the thermal envelope—the insulation and air barrier,” says NIST mechanical engineer Mark Davis. By nearly eliminating unintended air infiltration and doubling the insulation level in the walls and roof, the heating and cooling load was decreased dramatically.
The house was designed by Westford, Mass.–based Building Science Corp. to demonstrate net-zero capabilities, test advanced technologies, quantify energy use, and compare installed use with controlled use. No humans were allowed in the house during the year of testing. Instead, mechanical controls and computer software in the attached garage simulated the behavior of a family of four. The automated system controlled the lights, hot water, and appliances and even activated small devices that emitted heat and humidity to simulate living residents. NIST has made the data gathered during this yearlong experiment available online.
The year of testing, which ended July 1, was deemed a success: Despite a harsh winter that left the facility’s PV and solar thermal panels covered with snow on 38 days, the house produced 13,577 kilowatt hours of energy—491 kilowatt hours more than used by the house and its virtual occupants.
Although the renewable energy systems saved $4,373 in electricity payments over the year, front-end costs for solar panels, insulation, triple-paned windows, and other technologies aimed at achieving net-zero energy performance are sizable, according to an analysis by NIST economist Joshua Kneifel. In all, Kneifel estimates that incorporating all of the NZERTF’s energy-related technologies and efficiency-enhancing construction improvements would add about $162,700 to the price of a similar house built to comply with Maryland’s state building code.
Future research at the NZERTF will yield knowledge and tools to help trim this cost difference, says Hunter Fanney, an NIST mechanical engineer who led the research project. “From here on in, our job will be to develop tests and measurements that will help to improve the energy efficiency of the nation’s housing stock and support the development and adoption of cost-effective, net-zero energy designs and technologies, construction methods, and building codes,” he says.