After Gutenberg

A prototype of a Zero Energy Home using solar energy. Many such homes use more than one renewable energy technology. All employ passive solar design.

Let us revisit sustainable shelter with David Zaks and Jeff Christian. David interviewed Jeff for World Changing (January 30, 2007).

Jeff Christian directs the Buildings Technology Center at the Oak Ridge National Labs. Over the last four years he has conducted research on five prototype houses that cost between 60 cents and one dollar a day in energy costs to operate.

Jeff Christian works with Building America, a program that focuses on the building site, envelope, mechanical systems, and energy-use factors. Such homes optimize the following, energy efficiency and renewable energy features:

• Climate-specific design
• Passive solar heating and cooling
• Natural day-lighting
• Energy-efficient construction
• Energy-efficient appliances and lighting
• Solar thermal and solar electric systems.

Polystyrene Cement Board can be used to build floors, walls, and roofs quickly. Panels are prefabricated and transported to assembly site.

In the interview, Christian mentions working with low-cost SIPs (Structural Insulated Panels), which are comprised of a thick layer of foam (polystyrene or polyurethane) sandwiched between two layers of OSB (Oriented Strand Board), plywood or fiber-cement.

Bonding the foam core to the stiff outer skins creates a web-and-flange structural strength (along the same principal as an I-beam) across the length and breadth of the panel. With the capacity to handle axial, bending, racking, and shear loads, properly designed and assembled SIPs not only replace conventional framing, but will withstand high wind, and seismic forces. Toolbase Services – Technology Inventory

Indeed, one test house, the walls, floor and roof of which were made from expanded polystyrene panels clad with cement board, fit together without wood framing or braces, “remained fully intact after being shaken up harder than the strongest recorded earthquake.”

Electric radiant heat is easier to install, whereas a fluid system allows for more versatility in the heat source.

When using flooring with such material, another energy efficient approach is to install radiant heating. Technology available today allows control or modulate temperatures based on outdoor temperature. Sensors communicate with a microprocessor that is constantly processing all data to keep the radiant floor system running at maximum efficiency. While such a controller area network adds cost, it also over time brings savings because it matches heat input to heat loss at any given moment.

Ventilation is one of the problems associated with any super-tight, super-insulated, sustainable structure. (And, it follows that depending upon the area, Radon gas also could be a hazard.) Michael McDonough, AIA, NCARB, who has specialized in sustainable practices architecture for more than 20 years, advocates VDR (Vapor Diffusion Resisters) as one means of control over the amount of water vapor in the building. Geoff McDonell P.Eng. LEED AP focuses on energy recovery ventilation. He advocates designing the ventilation system to provide “touch-up” heating and cooling as necessary and as indicated by climate conditions. Other builders of Zero Energy Homes also emphasize the use of over-sized, interior-mounted ventilation ducts. All advocate a whole-building design approach to how energy consumption can be reduced.

A grid tie is implicit in the building of most Zero Energy Homes. The home owner is reimbursed for surplus electricity fed into the grid.

As Jeff Christian mentions in the World Changing interview, a Zero Energy Home consumes energy. It also produces it. The idea is that energy consumption of such intelligently designed homes results in a net usage of zero.

A grid tie enables an owner to sell any excess energy produced. Jeff notes that a big stepping stone was when (or if, in certain recalcitrant areas) utilities would buy back power.

According to Christian, for a group of test houses in Tennessee, the buy back rate needs to be at something like $0.22 – $0.23 for the homes as equipped to result in a zero cost (over an industry proscribed period for return on investment in the renewable energy technology). “Right now,” he says, “they (the utility) are buying back at about $0.15, so we are very close to that very critical stepping stone.” Which is a reason why proponents in the renewable energy industry are advocating that states encourage utility companies to institute feed-in tariffs that specify a guaranteed price for renewable energy. Usually, this price is a long-term, fixed rate not pegged to the retail price of energy. Builders are more like to install, and investors purchase, renewable energy technology when there is some assurance of an advantageous ROI (Return on Investment).