By Luis Gonzalez.
Last year, CleanTechnica reported a new project from the National Institute of Standards and Technology (NIST) about how to create a Net-Zero-Energy home. The results from the project have been disclosed after one year of experience with an excellent outcome. The residence achieved the goal of net-zero consumption with a surplus energy of 491 kWh.
A Net-Zero-Energy home is a residence that generates as much energy as it uses while meeting all the needs of the residents. The NIST net-zero-energy house was located in the suburbs of Maryland and has been used as a laboratory along a whole year, where a virtual family of four members spare energy in the same way a real average american family would do.
In order to achieve the net-zero consumption, the house was built up to U.S. Green Building Council LEED Platinum standards, the highest standard for sustainable structures in the country. Under these standards, the test house was estimated to be 60% more efficient than houses built to meet the requirements of the 2012 International Energy Conservation Code, the standards adopted for new constructions in Maryland.
The building was extremely well isolated, aiming to cut out air infiltration and heat looses in walls and the roof, including triple-paned windows. “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,” NIST mechanical engineer Mark Davis has declared. Apart of the insulation, the house got installed solar water heating and 32 solar panels in order to produce its own energy, and was equipped with the most energy-efficient appliances.
In a normal year, a comparable size home in Maryland would consume an average of almost 27,000 kWh of energy. Starting last summer, the solar panels produced more energy than the house used from July through October, but last winter was much colder than previous ones and the snow, double normal, covered during 38 days the sun-powered system. The house used 3,000 kWh more energy during the year of the study than it was projected for the region’s typical weather. In November, it began running negative numbers monthly and at the end of March the energy deficit was 1,800 kWh. In April, the energy yield increased again, and the house injected electric power to the grid on most of the days.
In total, the photovoltaics produced 13,577 kWh of energy, while the house only used 13,086 kWh in the whole year. The Net-Zero-Energy house from the NIST showed to be 70% more efficient, instead of the 60% initially estimated, than houses meeting the standards adopted in Maryland. The NIST suggests that a Net-Zero-Energy home could be combined with the use of an electric car to make use of this energy surplus, enough to drive an electric-powered vehicle for about 1,440 miles.
Although the extra investment needed to improve the efficiency, compared to the price of a similar construction complying with Maryland’s state building code, is calculated to be about $162,700, residents of these type of houses would save about $4,373 in electricity a year ($364 a month), and the improvements will not only increase the total value of the house, but it will also enhance the living comfort.
Along with the “Better Buildings Challenge” program of the Obama administration, many states are encouraging the construction of more efficient or even net-zero energy homes. For example, California aspires to enforce that all newly constructed homes are Net-Zero-Energy by 2020.
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