The 4,000-square-foot building is superinsulated and solar-heated. The building's designers wanted to create a building that was so good at capturing and retaining heat that it could offer livable conditions without a furnace.
It was insulated to double the requirements of the Pitkin County building code at the time of construction. The structure was also oriented to the south to better collect solar radiation, and it was built with a "tight" thermal envelope. While a less weather-tight house might experience a complete air change every hour, this building experiences a complete air change every ten hours or so (with the ventilators turned off, or up to considerably more than one air change per hour if they're all turned on).
The building is almost entirely lit by daylight. Its curved walls dampen interior noises and a central greenhouse humidifies the interior. These amenities make the building comfortable, and have significantly cut power demand and operational costs.
Much of the building's thermal performance is due to its advanced windows (often called "superwindows"), which were used here commercially for the first time. Virtually all are heavy-gas-filled Heat Mirror® windows. Heat Mirror® is a 0.002-inch (50-µm) clear polyester film with special, almost atomically thin, coatings that are transparent to visible light but reflect infrared (heat) rays.
The film is suspended between glass panes in a double-paned window unit and performs the way a third pane would perform—only better, because it keeps in more heat and lets in more light than a third piece of glass would. In fact, the type of Heat Mirror® film originally used in RMI's windows (Heat Mirror® 88, designed to maximize solar heating in cold climates) loses only about one-tenth as much heat as a single pane of glass, and lets in three-quarters of the visible light and half of the total solar energy.
During the 1990s, most of our building's original argon-filled, single-Heat Mirror® units were replaced with krypton-filled units having a double-sided film (Heat Mirror® coated on each side of a single suspended polyester film), and in some units supplemented by a low-emissivity (heat-reflecting) coating inside the outer lite of glass. The building's window configurations vary, but their light-reflecting and insulating capacities are keys to its efficiency.
The latest reglazing, in 2005–09, uses xenon fill and achieves center-of-glass R-values of 12.5 for all units except three that achieve R-20.0 via six selective surfaces.
The stone used in the walls is Dakota sandstone slabs harvested from the hillside a half-mile north of the site and hauled to the site in an old pickup truck. The walls were built using a technique called "slipforming," developed by architect Frank Lloyd Wright.
A pair of parallel, curving plywood forms was erected; insulating central foam, rebar, and any needed conduits, drains, structural pillars, etc. were placed inside; stones were placed inside up against the interior and exterior forms, and concrete was added in hand-scoops to fill in the space between the central foam layer and the forms, gradually building up each twenty-inch-high layer of masonry. When the forms were removed, excess concrete was removed with trowels, and the stones were washed. Overnight curing of the concrete permitted the forms to be raised twenty inches the next day in preparation for another "slip" the following day. The walls are constructed of two six-inch layers of this type of masonry with a four-inch layer of insulating foam sandwiched between.
Increasing insulation value in a house is one of the easiest and most cost-effective ways to save energy. These walls have an effective R-value of forty (~0.056 k), nearly double that of the wall of a conventional residential house. On the north side of the building, a solid concrete wall is predominately underground or "earth-bermed," which also helps to temper heat flow out of the building. The roof has an R-value of about eighty.
Tracking Photovoltaic Panels
A 2009 modernization added a 6-kW Sunpower array on the east roof and made the PV system islandable, so it runs with or without the grid. Ordinarily it sells back surplus solar power to the grid to displace coal. At night, the building runs on certified-additional purchased windpower.
The lower, main section of roof has two adjustable-tilt rows of photovoltaics (each with five panels apiece). These PVs don't track the sun, but they are raised and lowered seasonally to catch the sun's rays at better angles. They generate up to about two kilowatts of electricity. Their average annual output, about one-fourth as large, meets roughly a third of the building's electricity needs, nearly all of which are for the RMI office. Advances in PV technology enable today's panels to be much less conspicuous than these; indeed, modern PVs are designed so well they can be used as wall and roofing material.
Solar Hot Water System
There is a row of solar panels near the northern edge of the roof. They are one part of a system that heats water for domestic use. The water is first pre-warmed to about 68–105°F (19–40°C) as it passes through pipes in the concrete arch in the greenhouse below. These roof-mounted panels heat the lower layers of water stored in a 1,500-gallon tank under a closet in the residential part of the building. When someone turns on a faucet, water pre-heated in the greenhouse arch is drawn through a copper pipe immersed at the top of the tank, to which the hottest storage water rises. This secondary heat exchanger normally heats the domestic water to about 140°F (60°C). If needed, perhaps after a long period of winter cloud, a renewable-electric boiler in the workshop adds the last few degrees.
In 2009, the solar hot-water system was expanded to distribute hot water to radiant coils cast into the concrete floor slabs in 1983 but not previously connected. This is hoped to displace the woodstoves, which normally provide the last ~1% of space heating energy but were not used in the winter of 2009.