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Home Energy Magazine Online May/June 1994
TRENDS
Making Passive Solar Homes Affordable
Paul Neuffer got his start in the passive solar home business almost by
accident, 30 years ago. In 1964, he built a home for his family on a Nevada
site with a view of the Sierras to the south. Neuffer wanted a lot of glass on
the south of the house, to take advantage of the view, but he was also savvy
enough to minimize glazing on the other exposures. Furthermore, the steep lot
called for a high concrete foundation on the south, which was painted brown to
match the house's trim. An overhanging deck protected the foundation in the
summer. Neuffer put in a small woodstove and propane heat, and the family moved
in late that summer.
The happy accident of this house with a view is that it proved to be extremely
economical in terms of energy consumption. "I was shocked when I found out how
low the bills were, and I started checking into it," Neuffer said. "It made a
believer out of me."
When he went back and analyzed the design, he realized that he had constructed
a "passive solar home," intuitively. The overhangs were optimal, the windows
were just right. "I'd done everything perfectly, but it still didn't explain
why the house didn't cool off when the sun went down," Neuffer said. After
further investigation, he realized that the dark basement wall was storing heat
during the day and releasing it to warm the house throughout the night.
Neuffer mulled over these solar discoveries, and experimented with a few other
solar designs, finally offering solar models in 1978. Over the past ten
years, Neuffer Construction has sold more than 500 solar models, amounting to
about 25% of its total sales--and these days the passive solar models account
for about half of sales. Although Neuffer's marketing strategy is fairly
traditional--dwelling on more standard amenities and ignoring the solar
aspects--homebuyers have said that they picked a solar model because it was
"bright," or "full of light," or "open and airy."
"The trick to doing solar in competitive housing is you've got to forget about
building a house and adding solar to it. If nature made a goose that way, it
would never fly," Neuffer joked. In Neuffer's solar homes, windows serve as
solar collectors, and interior wall and floor surfaces double as thermal mass.
"There's got to be efficient use of materials," Neuffer said, "and dirt is the
cheapest thermal mass there is." He makes use of that cheap material to add
mass under the floors. "And it's hard to get anything cheaper than glass," he
continues. "Basically, you're talking about glass and mass. Combine those and
let them be the integral part of the house."
Neuffer Construction offers three solar options to customers. Model 1775, which
sells for $130,000, is a suntempered design with most of the glazing on the
south side, little on the north, and none on the east and west. (Model numbers
roughly correspond to square footage.) Because the cost per square foot for a
double-glazed window is about the same as the cost per square foot for a
standard exterior house wall, this model incurs no additional costs.
Model 2144 expands on the theme by lowering the southern-facing windows, and
extending them across the full width of the house, and adding tiled mass floors
behind them. This collector space is separated from the living room by a low
wall which helps cut glare. Construction of the thermal mass adds only about
$500 to the $160,000 cost of this model.
The third option, Neuffer's Model 1300 solar production house, is both the top
of the company's line in terms of solar performance, and its smallest and
lowest-cost entry-level home. The model offers a sunken solar gallery that is
separated from the living room by three steps and a low, 12-inch thick masonry
wall that doubles as a winter glare shield. The gallery's tile floor is placed
on a four-inch slab on compacted earthen storage, which in turn sits atop
two-inch foam insulation above the foundation. The placement of thermal mass in
the solar gallery enhances the convective movement of heat through the home by
allowing warm air to enter the living room over the low wall, and cool air to
enter the sunken gallery through the stair opening in the wall. The open
interior floor plan promotes distribution of this thermal energy throughout the
rest of the house. Even though the passive solar features add about $1,500 to
the cost of the home, it is still the company's lowest-cost model.
Solar Savings
According to Donald Aitken, a senior energy analyst with the Union of
Concerned Scientists, Neuffer's solar homes should use 25-60% less heating gas
than comparable conventional housing, for dollar savings of $140-$170 compared
to the average $400 winter gas bill in the area. Aitken says that the numbers
indicate 25% savings in winter heating bills for Model 1775, the suntempered
home, and 35% for Model 2144. Savings estimates for the Model 1300/1400 range
from 35%-60%. The Davis Energy Group arrived at savings of 35%-43% with a
thermal performance evaluation on Micropas 4 software, and Aitken arrived at a
figure of 60% with manual solar load and savings calculations. Aitken places
total savings for the Model 1300/1400 at about 50%. Actual gas bills for a
Model 1300 model home support those predictions. Compared to annual heating gas
consumption of 671 therms for a typical Reno-area home, 1300/1400 model home
used an average of two therms per day in December, three therms per day in
January and March, four in February, and one in November, April and May. Actual
consumption at the model house in January 1994--when the temperature averaged
34deg.--was 78 therms, for a $50 heating bill.
-- Abba Anderson
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