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The Net Zero Energy Test House Yields a Plus
July 3, 2014 | 6 Comments
The net-zero energy test house at the National Institute of Standards and Technology (NIST) in suburban Washington, D.C., absorbed a cold winter and produced a positive energy balance when it closed its one-year anniversary on July 1st. The surplus energy is said to about equal to powering an electric car rated at 2.94 miles per kilowatt hour for about 1,440 miles, approximating a month’s use.
Net Zero Home Snowed In. Click image for the largest view.
During the test including 38 days when the test house’s solar panels were covered with snow or ice, the Net-Zero Energy Residential Test Facility’s (NZERTF) sun-powered generation system produced 13,577 kilowatt hours of energy, some 491 kilowatt hours more than used by the house and its occupants, a computer-simulated family of two working parents and two children, ages 8 and 14.
First year energy use totaled 13,086 kilowatt hours, which was about 3,000 kilowatt hours more than projected usage in a year with typical weather. In a normal year, a comparable home built to meet the current Maryland’s residential energy standard would have consumed almost 27,000 kilowatt hours of energy.
At the location the estimated average annual bill for a comparable modern home could have been almost $4,400. For the virtual family of four residing in the all-electric test house they earned a credit by exporting the surplus energy to the local utility.
Hunter Fanney, the mechanical engineer who leads NZERTF-based research said, “We made it – and by a convincing margin. 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.”
The theory of a net-zero energy house is it produces at least as much energy as it consumes over the course of a year. A number of states are taking steps toward encouraging or even requiring construction of net-zero energy homes in the future. For example, California will require that, as of 2020, all newly constructed homes must be net-zero energy ready.
You may to get to buy this technology whether you want to or not.
NIST mechanical engineer Mark Davis gives us background with, “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.” By nearly eliminating the unintended air infiltration and doubling the insulation level in the walls and roof, the heating and cooling load was decreased dramatically.
The hard numbers are the NZERTF’s virtual residents saved $4,373 in electricity payments, or $364 a month. However, front-end costs for solar panels, added insulation, triple-paned windows, and other technologies and upgrades aimed at achieving net-zero energy performance are sizable, according to an analysis by NIST economist Joshua Kneifel.
How sizeable? In all, Kneifel estimates that incorporating all of the NZERTF home’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. For many Americans that’s an incredible and impractical number that alone will buy a nice house.
With good results and a huge upfront investment NZERTF has planned measurement-related research to yield knowledge and tools to help trim this cost difference. More research results also will be helpful in identifying affordable measures that will be most effective in reducing energy consumption. The extended research will further the development of tests and standards that are reliable benchmarks of energy efficiency and environmental performance overall, providing information useful to builders, home buyers, regulators and others.
Built as both a laboratory and a house, the two-story, four-bedroom, three-bath NZERTF home would blend in nicely in a new suburban subdivision. For the study it was designed and built to be about 60 percent more energy efficient than houses built to meet the requirements of the 2012 version of the International Energy Conservation Code, which Maryland has adopted.
The 2,700 square-foot (252-square-meter) test house is built to U.S. Green Building Council LEED Platinum standards – the highest standard for sustainable structures. Its features include energy-efficient construction and appliances, as well as energy-generating technologies, such as solar water heating and a solar photovoltaic system.
In terms of energy consumed per unit of living space -a measure of energy-use intensity – the house is calculated to be almost 70 percent more efficient than the average house in Washington, D.C., and nearby states.
From July through October, the facility registered monthly surpluses. In November, when space-heating demands increased and the declining angle of the sun reduced the energy output of its 32 solar panels, the NZERTF home began running monthly deficits. Through March 31, when the house’s net energy deficit plummeted to 1,800 kilowatt hours, roughly equivalent to the combined amount of energy a refrigerator and clothes dryer would use in a year, temperatures consistently averaged below normal.
Starting in April, the energy tide began to turn as the house began to export electric power to the grid on most days.
Of course the test home was a one time, custom designed and built experiment. Scaling up, mass market pricing and family budgeting would produce a much different result than the cost is no object government project approach.
Naturally the press release isn’t laying out what was bought and installed with an annual dollar amount available to use for substituting alternatives. Perhaps the data will appear on the site over time. If you see it leave word in the comments.
We need more data so the “low hanging fruit” choices are available quickly. Where the best “bang for the buck” part of the story hasn’t been shown. We taxpayers are waiting.
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For about one month, the panels were covered with snow and no energy was produced. For energy independence, nearly one months energy from other sources was used.
What would be the cost of this energy storage? This would also cover the daily variations. Maybe the gas/biofuel powered generators could be run for the season required.
so for an extra $160,000 initial price you save $360 month in electricity costs. Lets see, a 30 mortgage on $160,000 = $752 per month …
so for a net – $392 a month or $4,700 a year or $141,000 over the life of the mortgage you too can waste your money on going green …
I would also be more than a little worried about such a tight house and radon … you’ll notice they didn’t actually have anyone living in the house … opening doors and windows running showers and such … the “theory” sounds great … the real world may not be so cool …
The tightness isn’t a problem if you ventilate using a counter-current heat exchanger. In the 1990s my parents were living in an R2000 home in eastern Ontario with such a heat exchanger for ventilation. The heating was from grid electricity.
BTW the insulation was good enough that when the power was out due to the 1998 icestorm it was a few days before they had to drain the pipes & leave for a place with power.
In the 1990s my parents were living in an R2000 home in eastern Ontario with such a heat exchanger for ventilation. The heating was from grid electricity
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