Published on July 21st, 2014 | by Guest Contributor


The Results Of A 1-Year Net-Zero-Energy Home Case Study

July 21st, 2014 by  

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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  • Vince Stagbaugh

    $162,000 EXTRA to make this a zero-energy house??
    That is ridiculous.
    It wouldn’t take nearly that much to build net zero energy if you use the right materials to achieve the “thermal envelope.”

  • EVMan

    The numbers quoted don’t seem correct. The average cost of electricity in Maryland is 14.57 cents per kilowatt hour. The production of 13,577 kWh is only $1978 worth of electricity for the year – NOT $4,373. Payback is 82 years!! – ouch

    • Wayne Williamson

      I think they were looking and the 27mwh average usage.

  • Vensonata

    This story has done the rounds. Hasn’t it been up on clean technica before? Anyway the predictable reaction to the 160,000 extra cost…it is outlandish yes, but it is a “test house” nothing to do with a real house you would buy except to demonstrate that the building science works. They could have just asked the guys at ‘Green Building Advisor’ for free advice, lots of people have been there done that. Hire a German passivhaus builder already! Still, I am not complaining, the great housing revolution needs to begin yesterday.

  • Matt

    “$162,700, residents of these type of houses would save about $4,373”

    How can they have spent so much more? 40 years at zero interest to pay it off? A net-zero office can be built a no extra cost. WTF? You see passive homes in Europe that don’t cost that much more. Someone wanted to show it cost too much.

    • heinbloed

      Because it is a research project and research costs money.

      The cluttered fascade, the bad surface-to-volume ratio typical for a new world home plays an important role in the pricing as well.

      The Solar-plus houses are relativly new to the masses and are not to be compared to the already outdated “Passiv Haus” concept.

      It is a totally different concept.

      Search for the “solar decathlon” in the www. for more information on electricity generating houses, structures.

      • vensonata

        passiv haus is not outdated, but passive house is the U.S. version nuanced for this climate. One rethink is that since solar pv has fallen in price the last 10% attained through extreme air tightening and extraordinary insulation and $100 sq ft triple glazed windows could be more cheaply supplied by a few solar panels. This is a very recent realization.

  • No way

    How many kWhs did they get externally during the year in total? And how much external electricity did they need during the snowiest, coldest and darkest month of the year (most likely december or january)?

  • Kate Perry

    Google is paying 80$ per>>CLICK NEXT TAB FOR MORE INFO AND

    • Patrick Linsley

      Shouldda bought a net zero house with all of that extra money spambot.

  • DGW

    “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.”

    Just as there is enough food production to feed the entire planet except because of inefficient waste, energy is sinfully wasted only because it is so cheap in most wealthier nations.
    We could relatively easily cut fossil fuel burning in half with existing technology and a real commitment to care enough.

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