This article was originally published in the May/June 1994 issue of Home Energy Magazine. Some formatting inconsistencies may be evident in older archive content.



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Home Energy Magazine Online May/June 1994

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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