What do you get when you combine a super-tight, energy-efficient home with a large photovoltaic array and a solar hot water heater? You get a home that produces more energy than it consumes--in theory at least.
BUILDER's latest show home, the Ultimate Family Home, set to debut this January at the International Builders' Show in Las Vegas, will be a zero-energy home. That's the name the DOE has given to a new series of demonstration homes that produce at least half the energy they need to operate. The 5,200-square-foot Ultimate Family Home, built by Los Angeles-based Pardee Homes, will do much better than that.
"The home is predicted to produce more electricity than it uses," says Rob Hammon, a principal with ConSol, based in Stockton, Calif., the energy consultant to the project. That should include enough excess electricity to pay for the natural gas it needs. But that won't happen, Hammon says, because the local utility isn't required to buy back excess power produced by the house.
The show home was carefully sited on a lot in the Nevada Trails community, located near the foothills of the Spring Mountain Range, to reduce its southern exposure. Extra-deep eaves and trellises shade the main rooms. Two photovoltaic (PV) arrays, one delicately designed into a trellis network, the other on a back section of the roof, will produce a hefty 8.6 kW of electricity.
Natural gas will only be used to cook and for backup hot water. A solar hot water heater will meet most of the home's hot water needs. Only when the water temperature drops below a threshold will natural-gas--fired hot water heaters kick in. They are Rinnai tankless heaters that carry an energy factor of 0.82, about 50 percent more efficient than a typical gas water heater. "The home should produce 95 percent of the energy that it needs," says Joyce Mason, vice president of marketing for Pardee.
Sunny days ahead
Builder's show home comes at a time when the notion of home power generation seems to be gaining traction, especially in the West, where some utilities will subsidize the cost of PV systems. AstroPower, a Newark, Del.-based company that provided the system for the Ultimate Family Home, has been having a lot of success selling smaller solar systems that cover 25 percent to 50 percent of a home's energy needs. The packages sell for $12,000 to $24,000, but with rebates from utilities builders typically pay half that amount.
The show home is outfitted with a meter that tells homeowners how much energy they are producing and using, notes Addison Marks, builder sales manager for AstroPower. "When the solar-generated electricity is greater than the home consumption, the homeowner is spinning his utility meter backwards and getting a credit on his utility bill," he says. "When homeowners can see the power they are consuming, they often become more energy conscious."
ConSol worked with Pardee Homes to develop an ambitious set of energy details that reduce the resources needed to power the show home. They started with copious amounts of super-efficient fiberglass batt insulation from Johns Manville--R-38 in the ceiling and R-21 in the walls.
"Any of the extra deep cavities in the walls were filled up completely with insulation," says Bill Hughes, regional director of purchasing for Pardee in Las Vegas. "Some were as deep as 16 inches around the pop-out areas of the doors and window elevations." The loft ceiling received a layer of special ceiling batt insulation for use in tight spaces. A Tech Shield radiant barrier from LP Corp. lowers the attic temperature, increasing the efficiency of attic ducts.
"The duct system was designed by registered engineers--typical in Las Vegas but not elsewhere--to provide efficient but comfortable air conditioning," Hammon says. "The duct runs were shortened where possible by using side-wall registers then sealed to minimize air leakage. They also have a higher level of insulation and where possible are buried in the ceiling insulation."
The home was extensively sealed to prevent air leakage. Subcontractors sealed top and bottom plates as well as all exterior penetrations. ConSol will conduct a blower-door test later to verify air tightness.
The home's lighting--most of it fluorescent with halogen accents--was done within a strict budget of .5 kilowatts per square foot. Much of the light will come from 23-watt Genura lamps from General Electric that mimic the color rendition of incandescent light. They will be housed in fixtures from Riverside, N.J.-based Sea Gull Lighting Products that can take either incandescent or fluorescent lamps. Sea Gull provided a variety of low-voltage accent lighting as well.
Lower operating costs mean that homeowners can afford better windows, often the weak link in the energy package. The show home employs low-E, argon-filled windows and patio doors from Pella Windows and Doors. They carry strong solar heat gain coefficient ratings from 0.28 to 0.34 and U-factor ratings from 0.35 to 0.39.
Strict attention was paid to the energy efficiency of the home's appliances, starting with the HVAC system (with Honeywell controls and Goodman equipment) that carries a SEER value of 18, compared with the 10 to 12 found in most production houses. GE provided a complete line of Energy Star-rated appliances.
Achieving zero-energy usage still involves significant first costs, especially for this large show home. Pardee estimates that to buy and install the energy package in this home would cost more than $100,000, most of that for the photovoltaic units. But this home is bigger than most.
"We're saying that for a 3,000- to 4,000-square-foot home it would cost an extra $70,000 to achieve a zero-energy balance," says Lew Pratsch, who heads up the program at the DOE. "Right now, the PV is still the big expense to do that. We showed through our Build America program that the energy-efficiency part could be done at no expense."
Pratsch notes the program's success at showing that energy upgrades could be paid for out of savings from value-engineering--using less wood, right-sizing HVAC systems, improving duct runs, and more. These savings can theoretically offset the added cost of more efficient insulation, a premium HVAC system, and better windows and appliances.
|Code vs. Zero Energy|
|Specs for our zero-energy home vastly exceed those required by code. Here are a few of the major examples:|
|Wall exterior||R-13||R-21 (batt)|
|Attic radiant barrier||No||Yes|
|Slider||0.40 U value||0.33 U value|
|Patio doors||0.40 U value||0.33 U value|
|French doors||0.55 U value||0.33 U value|
|Furnace||0.80 AFUE||0.95 AFUE|
|Air conditioning||0 SEER||18 SEER|
|Duct insulation||R-4.2||R-6 (buried in insulation)|
|Water heating capacity||50 gallons||On demand|
|Energy rating||0.53||0.82 tankless|
|Photovoltaic system||No||Yes, 8.6 kW|
Learn more about markets featured in this article: Los Angeles, CA.