3 Homes Put Energy Ideas to the Test
By Tracy Idell Hamilton – Express-News
Web Posted: 07/14/2010 8:44 CDT
Editor’s note: This story originally appeared Sunday, July 11, exclusively in the print edition of the San Antonio Express-News. View full story on-line.
CPS Energy has taken a peek inside the future of home building — and so far, it likes what it sees.
The utility’s engineers are analyzing energy-use data from dozens of high-tech monitors at three homes with identical floor plans in Northwest San Antonio that were built last year to varying degrees of energy efficiency.
The U.S. Energy Department also is keeping an eye on the comparison as part of its larger effort to encourage cost-effective energy-efficient building technologies.
While the study is a little more than halfway complete, the homes already have yielded information that will benefit local customers. CPS is offering a new rebate for spray-foam insulation, which the study found saved more energy than expected because it seals a home’s “thermal envelope,” unlike fiberglass.
Another key finding: Orienting the solar tiles on the roof of one house to the southwest, rather than the south, resulted in a greater reduction in the home’s peak energy demand.
CPS is keen to reduce power consumption during peak times, such as the early evening, when most people come home, crank up their air conditioners, flip on the television and start cooking dinner. Peak power is the most costly energy a utility produces — a cost it passes on to the consumer.
Those and other findings will be crucial to the utility’s effort to conserve 771 megawatts of power by 2020, a cornerstone of its long-term energy plans.
Those savings would negate the need to build an additional power plant during that time, utility officials say.
To achieve those goals, CPS must understand which efficiency measures are most cost-effective in San Antonio’s climate. The utility will use the data it gathers from the homes to craft incentive packages for builders and homeowners to spur demand and drive up savings.
“CPS considers efficiency the fifth fuel,” after nuclear, natural gas, coal and renewables such as wind and solar, said Bruce Evans, director of customer solutions for the utility. “Reduction of use increases the available supply, so it’s also the cheapest and cleanest form of energy.”
Buildings use more energy than any other sector of the U.S. economy, according to the Energy Department, consuming more than 70 percent of electricity and more than 50 percent of natural gas. That means they’re also the largest emitter of carbon dioxide, a greenhouse gas most scientists say contributes to global warming.
Making buildings more efficient, according to the Energy Department, results in long-term cost savings for homeowners and businesses, reduces carbon-dioxide emissions and can also reduce peak energy demand.
Under its Mission Verde initiative, San Antonio approved rules last year that requires new homes be 15 percent more efficient than in the past.
The city later adopted the 2009 International Energy Conservation Code, which also requires increased energy-efficient measures. More stringent guidelines are expected under both international and local codes by 2012, and Mission Verde calls for carbon-neutral homes by 2030.
And while there are plenty of computer models that attempt to quantify the energy savings of a particular technology, CPS wanted to see real-world results specific to San Antonio’s climate.
Teaming up with Woodside Homes of South Texas, CPS subsidized the cost of building three homes, each one 2,027 square feet, in the Avalon subdivision off Old Prue Road.
One home was built to Woodside’s usual standards; it is supposed to be 10 percent more efficient than a home built to the building code standard in place at the time. It’s considered the control home.
The second has better insulation, more efficient heating and cooling systems and high-efficiency appliances. The third home has all that, plus a small array of solar roof tiles.
Unlike traditional solar panels, which are obtrusively bolted to a roof, the solar tiles are the same shape and thickness as the concrete tile on the rest of the roof.
The homes were sold, with the owners’ understanding that engineers would monitor their every energy move.
“They’ve been wonderful, very cooperative” about the intrusions, said Valerie von Schramm, senior research manager with CPS’ energy research and technology initiatives department, who’s leading the study.
The homeowners declined to be interviewed for this article.
Multiple meters and other instrumentation send energy-use data on each separate technology to CPS in 15-minute increments, allowing engineers to separate the effects of each.
For example, last month engineers could see the solar home, which has the best insulation, consumed 274 kilowatt hours for air conditioning. By comparison, the control home used almost four times that for its cooling needs.
Von Schramm and her team also learned through testing was that the control home actually was 14 percent more efficient than a home built to code, not 10.
“Woodside builds a tight home,” she said.
The two peak performance homes are even tighter, thanks in large part to the spray foam insulation.
The solar home, which uses spray foam in the walls and attic rather than fiberglass, had 70 percent fewer air changes per hour — used to measure the leak rate of a home — than the control home, while the middle home with some foam and some fiberglass had 40 percent fewer.
The solar tiles, while not enough to power the house entirely, did generate enough electricity to supply about 30 percent of the residents’ needs last month. In the afternoons, the tiles produced more electricity than needed, making the house a net power generator. And because the tiles were facing southwest, they sent energy to the grid later in the afternoon, when demand is peaking.
Researchers from the Florida Solar Energy Center, a research institution affiliated with the University of Central Florida, also are studying the homes as part of the Energy Department’s Building America Industrialized Housing Partnership program, which aims to reduce the energy cost of housing by 30 percent to 70 percent.
Dave Chasar, a senior research engineer with FSEC, says it’s invaluable that CPS has invested in three different homes with different levels of efficiency. Most of the test homes in its program, he said, are stand-alone affairs.
Studying three “with the same weather, the same floor plan, that’s unique,” he said. “We really have a way to compare (different building technologies) very directly.”
At this point, engineers mainly are analyzing how the different technologies impact energy use in each house. They have 10 months of data now, and will keep monitoring for another six months — or longer, if the homeowners agree.
The next step for CPS, said Cris Eugster, the utility’s chief sustainability officer, will be to calculate which efforts will give home builders or owners the biggest bang for their buck.
Because the impact of the spray foam insulation was so impressive, he said, the utility wanted to get a rebate program up and running, but it still will crunch the numbers.
“Is it a three-year payback or a 10-year payback? It’s too early to say right now, but if it’s shorter, we want to encourage even more people to do it. (Spray foam insulation) could be a big deal here.”
CPS’ rebate is only for existing homes at this point, as is the federal tax credit available for spray foam. The utility’s website includes a list of approved contractors.
The foam works so well because it effectively cuts off air flow by sealing small cracks in the home. Previously, the utility recommended fiberglass batting of at least a 6-inch thickness, which von Schramm said could be “extremely expensive” — and it still doesn’t cut air flow.
Spray foam works better, she said, “and now we have the data to prove it.”
CPS’ findings are in line with national guidelines.
The Environmental Protection Agency and DOE are updating their Energy Star home requirements, which will have an increased focus on reducing air flow and tightly sealing a home’s thermal envelope.
Making sure those improvements are affordable is a major focus for the federal agencies and CPS, which carefully weighed the costs of the upgrades added to the three test homes.
“We knew we could build a million-dollar home,” and create a “net-zero” house, or one that produces 100 percent of its own power needs, von Schramm said. “We wanted to know, ‘What would it take to build something affordable?’ ”
Still, the utility spent about $68,000 on upgrades, costs which weren’t entirely passed on to the buyers, said Peter Evans, division president of Woodside Homes. About $24,000 of that went for the solar tiles, about $6,000 more than a similar-size system using standard photovoltaic panels.
“It was easy to sell all three homes, but only because CPS subsidized the cost,” he said. For example, the asking price for the solar home was $261,000, but including all the upgrades, it would have cost closer to $300,000.
Evans said he didn’t think, given the economy, that most homebuyers are ready to pay such a premium. But CPS’ research should benefit existing homeowners as well.
The utility plans to spend more than $150 million to weatherize homes for low-income residents in the next decade as part of its efforts to reduce consumption, and it will incorporate the most effective technologies that come out of this study to do so.
But even with all the cutting-edge technology, home energy savings often comes down to personal habits. “Once you get the envelope under control, the rest of the energy use is up to the homeowners,” von Schramm said. “If they want to lower their bills, they can.”
Family size also plays a part. The control and solar homes have similar-size families, while a smaller family lives in the middle home.
So, for example, the solar family consumed more kilowatt hours of power in the month of June than the single person, even with the offset of 345 kilowatts hours generated by the solar tiles.
Water use is similarly affected by family size and habit.
“The solar family is using 14 percent less water,” von Schramm said. “So they will save energy because they use less water and also because their water heater is almost 25 percent more efficient.”
3 Homes Put Energy Ideas to the Test