This article focuses on the research and development projects to ensure homes and office buildings implement the concept of zero net energy, i.e. self-sufficient in energy buildings. Net-zero commercial construction has doubled since 2008. Reducing energy consumption on the inside depends on ultra-efficient appliances, high-performance heating, ventilation, and air conditioning (HVAC) systems, geothermal heat pumps, and lighting controls. Impressive advances are occurring in the field of solid-state lighting technology, which has the potential to reduce U.S. lighting energy usage by nearly 50%. The solar-energy technology company Vivint partnered with Garbett Homes to take on one of the biggest challenges for net-zero housing: creating designs that work in cold climates. The house that Vivint and Garbett built in Herriman, Utah, attained a Home Energy Rating System score of zero, indicating that the home is completely self-sustaining. The Habitat for Humanity house, in particular, shows how affordable zero net energy homes can be – especially for lower income homeowners.
Completely energy-sufficient households sound like something out of Doomsday Preppers—the kind of houses that have barrels of freeze-dried food in the cellar and hoards of gold stashed under the floorboards. But constructing highly energy-efficient dwellings that produce as much energy as they use is not a far-out idea. Traditional buildings consume about 40 percent of the total fossil fuel energy produced in the U.S. That makes striving toward energy self-sufficient buildings—what’s known as zero net energy housing—a great way to cut greenhouse gas emissions and reduce dependence on fossil fuels.
Today, builders aren’t just striving toward the zero net energy goal, they’re achieving it. Energy efficiency is being achieved through greenbuilding techniques and high-efficiency appliances, HVAC, and lighting systems. On-site renewable energy (mostly solar) provides energy to run the home. Over time, energy consumption balances out energy production, resulting in a zero net energy bill. (Sometimes a home can have an energy surplus, which is usually sold back to the grid.)
Even so, prospective home buyers are more likely to be concerned with kitchen countertops than the net energy balance of the building. That’s because zero net energy homes are considered far too expensive for most Americans to build. But this, too, is starting to change. Thanks to new technologies, lower-cost manufacturing, and significant tax incentives, the out-ofpocket cost of building a zero net energy house is lower than ever. For example, in New York, home owners can receive tax credits of $20,000 or more for buying or building a zero net energy home.
The U.S. government is serious about zero net energy, too. It has mandated that federal buildings must be zero net energy by 2030. Federal incentives are also available for commercial and residential construction.
Net-zero commercial construction has doubled since 2008
“Thanks to advances in structural insulation, energy-efficient appliances, new government incentives, and the falling price of solar, expensive green-building projects-like net zero—are now within reach,” writes Lacey Johnson in the March 2012 Scientific American. “And they don’t always require a commercial-scale budget.”
The energy flow of a typical building involves tapping off-site energy sources—grid electricity and fuel delivered via pipe or truck—and using that to provide heat and power for various appliances. To achieve zero net energy consumption, a building must generally provide its own on-site power generation, be equipped with energy efficient appliances, and have a design that reduces the need for artificial heat and light.
That last part is relatively straightforward. There are many proven construction methods for building an energy-efficient shell, including the orientation of the home, air barrier systems, advanced insulation systems, window and door materials, daylighting, and sun control and shading.
Reducing energy consumption on the inside depends on ultraefficient appliances, high-performance HVAC systems, geothermal heat pumps, and lighting controls. Impressive advances are occurring in the field of solid-state lighting technology, which has the potential to reduce U.S. lighting energy usage by nearly 50 percent. Department of Energy funding has been instrumental in supporting R&D for standard light-emitting diode and organic LED technologies.
Such approaches may greatly reduce a building’s energy consumption, but it still needs energy to operate. The only wayto achieve zero net energy is by using on-site energy-generating technologies. Solar is the most common, both for home heat and water heating. Some homes use wind turbines. Other alternatives for on-site, renewable energy production include burning biomass to create energy for certain parts of the home, or for hot water. When deciding on the energy system, it is important to consider availability of the energy source, reliability, system maintenance, and life-cycle costs over time.
Zero net energy homes still need to be connected to the electric grid for those times when their on-site systems cannot meet required energy loads. In some states, excess energy that is produced can be sent to the electric grid and credited to the owner’s electric bill. When a home is truly zero net energy, the only bill from the utility company is a monthly charge for being connected to the grid.
Several building projects in recent years have achieved (or come tantalizingly close to) zero net energy
One of the first government buildings to reach zero net energy status is a 7,000-square-foot office building at Oak Ridge National Laboratory in Tennessee. About $150,000 was spent on retrofits in 2009 and 2010, which reduced the building’s energy usage by 40 percent. Its operational energy needs were supplied by a 51 kW solar array.
The lab also implemented software to shut down computers and other electronic equipment at night. “It’s surprising how much energy computers use,” said Norman Durfee, senior project manager at Oak Ridge National Laboratory. “Because our measures with powering off computers were so successful, this has now been implemented across all of Oak Ridge National Laboratory.”
Another government agency, the National Institute of Standards and Technology, in 2012 opened a new laboratory which goes by the snazzy acronym, “NZERTF,” short for the Net-Zero Energy Residential Test Facility. NZERTF is a 2,700-square-foot, four- bedroom home in suburban Maryland built using energy-efficient construction and tricked out with energy-efficient appliances, solar photovoltaic systems, solar water heating, and geothermal heat pumps. The goal was to demonstrate that a typical residential home can meet zero-net standards.
Results thus far have been successful. The test facility generated a surplus 491 kilowatt-hours of energy in its first year of operation.
But for zero net energy buildings to have an impact, they will have to be lived in. Construction companies and non-profit organizations are working to develop the technology and experience to build energy-efficient housing.
Last year, for instance, the solar-energy technology company Vivint partnered with Garbett Homes to take on one of the biggest challenges for net-zero housing: creating designs that work in cold climates. The house that Vivint and Garbett built in Herri- man, Utah, attained a Home Energy Rating System score of zero, indicating that the home is completely self-sustaining. The HERS Index, established by the Residential Energy Services Network, is the industry standard for measuring a home’s energy efficiency.
The companies maintain this is the first zero net energy home design that is highly replicable and scalable, and the starting price of $350,000 isn’t much different from other high-end houses.
Impressively, though, Herriman is in the same climate zone as northern Idaho or parts of upstate New York. The project also demonstrates how important solar energy is for achieving zero net energy. Vivint’s solar energy system dropped the HERS score by 23 points.
UC-Davis West Village at the University of California-Davis is one of the largest planned zero net energy communities in the country. Opened in 2011, West Village is home to the university’s research efforts on energy efficiency and sustainability. In 2014 Honda opened its new zero net energy home on the campus. The home generates enough excess energy to power a Honda Fit EV for daily commuting.
LED lighting produces 40 to 100 lumens per watt, which is five times more energy efficient than traditional incandescent bulbs. Such super-efficient lighting is used throughout the homes in West Village. But the homes also feature a circadian rhythm- friendly lighting system that mimics natural shifts in daylight that occur throughout the day. That feature enables occupants to select lighting scenes that complement their own circadian rhythms, and better support night vision and overall wellness.
Perhaps the most impressive zero net energy accomplishment comes from Minneapolis.
Twin Cities Habitat for Humanity and its partners, including University of Minnesota’s School of Architecture and Design and Center for Sustainable Research, built an affordable, net zero energy house in 2013. Habitat for Humanity says it’s the first net-zero home built by an affordable housing developer.
“What is most exciting about this achievement is that the home, which is based on Habitat for Humanity's relatively modest home designs, shows that a net zero energy home is not just a possibility for the wealthy,” said Chad Dipman, project manager for Twin Cities Habitat for Humanity. “It also highlights the fact that net zero energy homes are especially suited for lower-income families. Ideally, the homeowner will not have to pay any utility bills at all. And,since the home is connected to the energy grid, any extra electricity it produces can be sold back to the system.”
Habitat for Humanity's Minneapolis home scored a four on the HERS scale. “A typical new home built to Minnesota's energy code, which is stricter than most other states, receives a HERS rating of 62,” Dipman said. “The Twin Cities Habitat Net Zero house reduces carbon emissions by 16.7 tons per year, sulfuric oxide emissions by 50.6 pounds per year, and nitrogen oxide emissions by 40.3 pounds per year, compared to the typical new Minnesota home.”
Key energy-efficiency elements in the home include solar thermal panels, two air-to-air heat exchangers, improved insulation, triple-pane casement windows throughout the house, and a special coating on south-facing windows to collect energy in the winter.
“The low-income family that owns the net-zero home will save about $2,200 per year in utility costs, compared to a home built to Minnesota energy code standards,” Dipman said. “This amount is tremendously significant for a Habitat family, whose average income is less than $35,000 for a family of five.”
That sort of demonstrable savings has led to growing support—from nonprofits like Habitat for Humanity to the construction industry to the federal government—to build zero net energy buildings. The Department of Energy, for instance, has been extremely supportive of zero net energy residential and commercial buildings. One of its top priorities is to help zero net energy homes become an affordable reality by 2020 (and commercial buildings by 2025). Government agencies, national laboratories, universities, and the private sector are working hard—often in partnership with one another—to advance zero net energy-related research.
For example, a UCLA research team is studying new materials and technologies for zero net energy buildings. One of their projects involves mixing capsules of phasechange materials similar to paraffi n wax, 10 to 100 micrometers in size, into concrete that is poured for wall panels. The capsules absorb heat during the day as the wax melts at a constant temperature. At night, as the building cools, the capsules release energy as the wax solidifi es. The phasechange ability allows building materials to passively absorb and release heat for maximum effi ciency. The materials help a building's heating and cooling systems do their jobs, but without the need for fuel. So far results show a 15 to 20 percent improvement in energy effi ciency.
Ultimately, cost will be the driving factor in the widespread acceptance of zero net energy construction. The cost difference between a regular home and NIST's residential test facility is about $160,000. It would take a family 28 years to earn back the extra cost of this net zero energy home through energy savings alone.
Part of the research effort involves understanding which effi ciency technologies produce the most proverbial bang for the buck. Energy modeling can help determine which green elements are most cost-effective and energy-efficient for a given site. State and federal incentives, when combined with energy-saving building methods and the latest heating and cooling technologies, can reduce the total out-of-pocket cost of a net zero energy home to as little as 5 to 10 percent more than a new conventional home. That cuts the time to recouping the investment to as little as 10 years.
The Habitat for Humanity house, in particular, shows how affordable zero net energy homes can be—especially for lower-income homeowners. “With our standard design as a basis, this project shows that a net-zero home can be built for just over $200,000,” Dipman said. “Commercial developers could also replicate our model and scale it up to meet—or create—middle-class consumer demand. Such a movement would have a huge environmental impact.”
Nergy Efficient Housing Doesn't have to be Built from Scratch. Purdue University has Partnered with Whirlpool Corp. on a Three- Year Project to Convert an Exist- Ing Home in West Lafayette, Ind., Into a Net Zero Energy Structure.
Called the ReNEWW house (Retrofitted Net Zero Energy, Water, and Waste), it will be retrofitted with energy- and water-saving features and equipped with solar panels to produce electricity and hot water.
“So much of the net zero energy discussion now focuses on new buildings,” said Eckhard Groll, a professor of mechanical engineering and director of Purdue’s Office of Professional Practice. "But most homes are existing structures.”
The housing stock in the United States has more than 130 million units, most of which have been in existence since the 1970s. Even if every new house was a zero net energy building—an impossibility—the effect of that effort would be blunted by millions of inefficient houses that still have decades of productive life left in them.
The ReNEWW house was built in the 1920s.
Whirlpool engineers will come to Purdue as graduate students and live in the house for two semesters as part of the Whirlpool Engineering Rotational Leadership Development (WERLD) program. They will take long-distance courses through Purdue's engineering professional education program while they collect baseline energy and water consumption data that the company can use to develop next-generation, ultra-efficient appliances.
“The ReNEWW house will allow Whirlpool Corporation to leverage the world-class resources at Purdue University, in conjunction with our WERLD program, to accelerate the development of the next-generation system of innovative home appliances that offer even more performance without compromise,” said Ronald Voglewede, global sustainability lead for Whirlpool.