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Net-zero energy test home ends year-long study with surplus energy


July 10, 2014

The net-zero test home at the National Institute of Standards and Technology (NIST)

The net-zero test home at the National Institute of Standards and Technology (NIST)

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Braving a harsh winter with snow-covered solar panels, the Net-Zero Energy Residential Test Facility (NZERTF) in Washington DC has come up trumps in a year-long study of its energy harvesting capabilities. Located on campus at the National Institute of Standards and Technology (NIST), researchers used computer simulation to replicate the energy consumption of a family of four. At the end of its first 12 months, there was a large enough surplus to power an electric car for 1,440 miles (2,317 km).

The 2,700 ft sq (252 sq m) two-story construction was developed to look like a regular home, but function as a laboratory for clean energy research. Much like the Honda Smart Home, NIST's effort combines stable ground temperatures with geothermal systems to minimize heating and cooling loads throughout the building. Another factor in overall energy efficiency is a doubling of insulation levels, sealed by special sheeting that reportedly heals itself when pierced.

"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.

On July 1 2013, the research team began the experiment by moving a virtual family into the home. A computer simulator syndicated the energy consumption with that of a typical American family of four, the inhabitants going about everyday activities such as taking showers, watching TV and charging laptops. There was more at play than a life-sized game of The Sims, however, with the researchers able to gain realistic insights into the energy efficiency and how viable planting such a home into a real-life American neighborhood could be.

The energy surplus and the home's claim to net-zero living was compounded by a stretch of severe weather. For 38 days through winter, the 32 photovoltaic panels were largely covered in snow and ice, hampering their ability to harvest energy from the sun. But over the 12 month period, the home generated 13,577 kWh of energy. This surpassed the virtual family's energy usage by 491 kWh, an excess that could in theory be directed toward an electric vehicle or back into the grid.

"We made it, and by a convincing margin," said Hunter Fanney, the mechanical engineer who leads NZERTF-based research. "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."

Despite boasting the aesthetics of a typical suburban house, adoption of the technologies used will largely come down to cost. NIST estimates that fitting out a similar-sized house with all the bells and whistles of its test home would cost around US$162,700. On the upside, it puts savings in electricity costs at $4,373 for the year.

Further research will center on how the measurements of the home can improve its energy efficiency and addressing the difference in up-front costs and long term savings. NIST is hopeful its findings will lead to improved energy efficiency standards as a resource for builders, regulators and home buyers.

The video below gives an overview of the project.

Source: NIST

About the Author
Nick Lavars Nick was born outside of Melbourne, Australia, with a general curiosity that has drawn him to some distant (and very cold) places. Somewhere between enduring a winter in the Canadian Rockies and trekking through Chilean Patagonia, he graduated from university and pursued a career in journalism. Having worked for publications such as The Santiago Times and The Conversation, he now writes for Gizmag from Melbourne, excited by tech and all forms of innovation, the city's bizarre weather and curried egg sandwiches. All articles by Nick Lavars

So it only takes 37 years to pay all the systems off? Sign me up! That sounds like the deal of a lifetime!

In all seriousness, it is great that they proved what they did but until prices become more realistic there won't be enough people who can afford to do this.


Of course it would not do near as well with a real family living in it with the children leaving doors open, people staring in the fridge, and of course light left on all the time.


@ Slowburn:

They said their energy-usage was exactly the average.

So, being an average... everything you mention has already been factored in... along with the intelligent kids/adults who know how to shut-doors and turn-off lights.


@ Milton I know what they said it is just I don't believe they got it right.


I agree with Slowburn - A useful exercise, but it could prove difficult to duplicate in a real life situation,no matter how "average" the computer simulations are. You could probably up the power usage by 10% with a real family. That negates the power surplus so you are left with a fairly expensive (although maybe usefully off-grid somewhere) home to pay off.

The Skud

Also average means that half is higher.


Send the virtual kid up to clean the snow off the panels and performance would have been even better. And for his allowance - bitcoins.

Mark A

Please take note, a real family did not live In this house. A computer lived in the house and was programed to 'average' but not real. With all the homeless families out there don't you think this outfit could have moved a real family into the house rent free and obtained a more accurate assessment of real life.

I know people who live off grid in Colorado and they need back up generators when the sun dosen't shine and the wind doesn't blow.

This was likely a grant funded project designed to show a predictable result.


All y'all, Some important factors are missing from your criticisms of the value of the project. Before laying out a judgment, how about getting all the relevant information?

For example, while the article states savings on electricity, it doesn't state savings on fuel for heating, perhaps substantial due to the better air barrier and insulation, or for a car (replaced by elec, as noted). So, we don't have enough info to calculate payback time.

Payback time doesn't matter much if I finance it with PACE loans, so the cost stays with the house, not with the borrower; so I can move to another house before it pays back fully and not lose money. I hear of more and more places where that is becoming an option.

Houses that are sealed and insulated well tend to be more evenly comfortable throughout the spaces, throughout time. What value of happiness?

They tend to be more healthful places. What value of not getting sick as much?

As energy rates rise, per the long term trend, the rate of savings increases. So, payback time occurs faster than the calculations in these comments.

Currently, the initial cost can be reduced in a few ways. First, some energy systems (like solar power, solar thermal, etc.) can be leased; little or no upfront cost; system designed to optimize your expenses & savings. Also, there are federal tax credits for power systems (30% cost reduction) and tax credits or cash rebates in various states and utility districts. These often lead to a total cost reduction of 50% to 60%, thereby reducing payback time. There are state and district incentives for energy efficient construction (air barrier, insulation, better furnace, better duct design, etc.). Those reduce the cost noted here.

How about home value? If you sell a home with solar power and a record of lower heating bills, plus good testimonials about comfort, how much more would you get in the sale? If you show a banker that your operating cost is lower than usual, what better terms on a loan for a car or a business startup could you get?

Very few homes are off the grid. That comment about people in Colorado is not relevant enough to reject the project in general. In most places, a home with a solar power systems is required to be connected to the grid, if it is already on the grid. So, the grid provides power when the home system doesn't generate. If the grid goes down, you can still get power during generating times (if you have the right kind of inverter, like Sunny Island as well as the common Sunny Boy). Then, sure, you can have batteries for the rare times when the grid is down and there is no home power generation.

Generally, the article is incomplete, lacks many of the benefits in a cost-benefit analysis. No assessment can be made, with integrity.

Would you want someone to evaluate you, without considering all of your virtues?

Greg Proefrock

How can they only use 491kWH a month? I average 1,550 a month and have a new home very well insulated.


All research by definition creates a problem model that limits and smooths the variables. This is necessary in order to be sure of what is being tested. So quit whining about how much reality might vary. Vehicle mileage, freezer/fridge annual costs, etc., are all estimates. Your mileage will vary. Next, all the major and many of the minor elements here are evolving. Solar PV is getting much cheaper and incrementally more efficient. If recent innovations in sturdy AEROGELS pan out it should soon be possible AND affordable to have R40 to 60 insulation in the walls. Kinda makes losses through glass unimportant but the same aerogel researchers are trying to find an aerogel that is totally transparent. The big point in this NIST study is that with better materials and engineering any home can effectively dropped off the grid as a load element. At any one point in time such a home (and also most any business), may or will draw some electricity or fuel but overall the draw can be nearly to actually zero. And, the costs are getting progressively, incrementally better all the time.


The problem is they're still sucking on the grid teat. They get free power when the weather is bright and sunny, but they contribute nothing when the demand is greatest, when the weather is bad.

As a result the grid generators and distribution lines still have to be provisioned to allow for the worst case demand conditions. People without solar are paying a disproportionate amount for grid upkeep while solar users get to skim it in emergencies.


Did they have the doors, including Garage door, opening and closing regular and sometimes odd hours; or like a party, or kids running out and leaving it ajar for an hour now and then?


You can assemble solar panels at a cost of 1 dollar per watt for yourself and that home had more space to cover with an out building that could be used. If they had made the walls out of Cob they would have had better thermal properties at 1/100 the cost. If they incorporated a methane digester tank for the families sewage they would have had a power source that operates rain or shine and their food bill would cover energy needs. Add in rain collection and their water bill would disappear or be dramatically reduced. You can find out how to do all this now on Youtube you don't need nanny's permission to invest and then run your families budget in the black making your home earn you money rather than cost you money.


It is the same as a cpu. Price goes down, efficiency goes up. Think of where this will be in 8-16 years.

The other side is that price of fuel and electricity goes up every year so it will eventually be like the iphone, you aren't cool if you don't have one or if it isn't close enough to the newest version and by not cool I mean you would be stupid not to have solar pay for most if not all of your electricity and gas for your car.

Ben O'Brien

Wombat: Foolish Argument. Knocking improving energy efficiency is counterproductive and useless. Over time as component technologies are deployed, improved upon, and then deployed some more everyone will consume less from the grid. As this happens society will be affected progressively less by large scale weather events and abrupt shifts in energy costs. In a sense making progressive energy efficiency improvements dampens society's sensitivity to external events. This is universally a great objective. Also making buildings thermally more efficient not only reduces energy consumption in any form but will progressively reduce the "Heat Island" effect that all of our currently leaky buildings have nationwide & worldwide. It will take time but doing this small scale work to individually limit energy consumption will limit our effect on weather over time. Currently about 30% to 40%of nationwide energy consumption goes just for lighting & space heating or cooling. Better engineering and materials coupled with solar PV, Wind & geothermal could bring these numbers very nearly to zero and maybe to a net gain. Energy returned to the grid from anywhere can always be used somewhere. This is an accomplishment & not something to whine about.


The moment they said they used a computer simulation you know the results will be off by at least a factor of five.

Now they must run the experiment for another year using real people which will give them real results - by real people I mean people that act as normal people would and not stop to decide if what they want to do would be in the best interests of the experiment.

I think that Slowburn has the right Idea that in a real use situation the results would not be very good at all.


Using real people, as in a family that invested in the energy saving devices used in this home might also be energy conscious in their own habits and not leave the doors open and the lights on.

Real people might use less energy than the computer simulation.

Why would using a computer cause the results to be off by a factor of five? Having real people living in the house could make monitoring and maintaining the devices difficult.

It would be interesting to know all the details of how they built the house and what methods they used to save energy. Insulation would be obvious but how much and what kind. The solar electric and solar water are obvious but no details as to capacity etc. What kind of windows. Geothermal heating?

When I lived near Madison, WI we had some very cold winters – highs below zero for a couple of weeks straight. We had a 5 x 16 foot concrete porch on the South side of the garage that I enclosed with 2x4 studs and cheap, translucent, plastic sheeting. I put 4 foot high plywood painted black on the inside of the studs and raised 4 inches from the floor. We made a 10 inch dia. hole for the cat next to the storm door at the far end. We found that we could leave the front door open and if the wind was blowing from the West (through the cat door) the porch would keep the house warm in below zero temps.

It could have been made better but I was just trying to keep the cold air from blowing inside every time the front door was opened by enclosing the porch and adding a storm door at the far end. The black plywood was an afterthought and the cat door did not stay closed when the wind blew so we took just it off. I was amazed at how much heat we got.

Most houses are designed more for low build cost than low operating cost.

More projects like this will help to change that for the benefit of us all, even those that watch TV 24/7 and leave the lights on and the doors open and live in houses built before insulation was used in the walls.


@ Greg Proefrock - Even if all $162,700 were financed through PACE loans, it still amounts to $675 per month for a 20 year note or $903 per month on a 15 year note (both of which seem to be the normal range). Money that may end up being lost because there will, more than likely, be no way to recoupe it in a sell.

"If you sell a home with solar power and a record of lower heating bills, plus good testimonials about comfort, how much more would you get in the sale?" These things are irrelevant. I just (26th of June) closed on a townhome which I purchased at $185,000. The original owner purchased it new in 2007 for $238,000 because they opted in for all of the upgrades. When all was said and done, the majority of other homes in the area were of lesser quality by options and therefore less cost to purchase. These homes drove the sell price of $185K. The point is, that the house, regardless of what bells and whistles may be installed is still only worth what the market will actually support.

As far as the car, no electric car was noted in the project. It was only stated that there was enough surplus to take an electric car 1400 miles. That's all good and fine but it was not part of the project and electric cars are far from being the average car.

How is the comment about generators being needed in Colorado irrelevant? How is your comment any more relevant?


A normal person thinks in terms or 5-10 years payout. 37 years payout for improved energy efficiency just doesn't cut it! And w/i that 37 years consider the cost of replacements, repairs, upgrades, etc.

No, not doing it for me!!

Brian Allan
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