It’s pretty much a given that a household consumes energy—in some cases a lot of energy. But, improbable at it sounds, what about a house that actually generates as much energy as it consumes?
That’s the concept behind the “Net Zero” College House in Tifton, GA, a demonstration home developed by the University of Georgia, Moultrie Technical College, and the Tift County Foundation for Educational Excellence. This greenest of green homes features a wide range of industry best practices and high-efficiency technologies, including the Voltex® heat pump water heater from A. O. Smith.
One of the visionaries behind the 1,800 square foot house is Tony Grahame, a Green Building Technology Faculty member University of Georgia-College of Agriculture and Environmental Sciences and a long-time practitioner of high-efficiency building practices. “One of the major objectives of the College House project, is to teach people that a house needs to be designed and constructed as a system--how all the building components must work in harmony to create indoor conditioned spaces that feel safe, comfortable, healthy, and exhibit resource efficiency and durability,” he observes.
In terms of energy efficiency, the College House goes where few houses have gone before. The generally accepted standard for a new home in the U. S., according to the Home Energy Rating Standard® index (HERS) is 100, Grahame explains. An Energy Star® home would come in at 70, and 50 would be a “very good score,” he continues. “Pushing the house to 40 would make it 60 percent more energy efficient than a 2006 IRC code compliant house.”
Getting the HERS index to zero required a number of innovative technologies including photovoltaic solar panels on the roof that help generate electricity. The Voltex hybrid heat pump water heater made a significant difference by lowering the home’s efficiency energy rating by seven points – that is a huge number when you already have a score in the 50’s.
“This is a ‘green’ building, not an alternative building,” Grahame stresses. “We made good practical choices in terms of site selection, design strategies, and the selection of appropriate, ‘climate specific’ building materials, systems and technologies.” The house was built to be durable, easy to maintain, with extremely low operating costs.
The focus on energy savings, however, was designed literally from the ground up. The perimeter of the slab of the home is insulated, since between 30 and 50 percent of heat loss occurs through the slab in a heating dominated climate, Grahame explains. The walls are constructed with 2” X 6” studs, 24 inch on center. This helps to minimize framing material, thermal bridging, and maximizes amounts of insulation. South facing windows were selected to maximize solar heat gain during cold months, and all the other windows had a very a very low SHGC (solar heat gain coefficient) to resist heat gain and loss through the glazing. Students from MCC did most of the construction as part of their coursework, although Grahame did employ contractors, that worked with the students, to install the plumbing, residential wiring, and HVAC system.
When he first began designing the Net Zero house, Grahame looked into solar water heating system, however, the use of the photovoltaic panels limited the amount of roof space to allow for a solar water heating system. He also encountered difficulty identifying a systems integrator capable of handling a solar water heating installation. Through his research, he found A. O. Smith and its line of renewable water heating solutions. An article from the Southface Energy Institute of Atlanta encouraged him to pursue heat pump water heater technology.
The Voltex heat pump water heater operates under the same principles as a refrigerator, only in reverse. It pulls in warm surrounding air; heat from the air gets absorbed in the refrigerant that runs through a compressor increasing its temperature. The hot refrigerant then circulates through coils that surround the water heater tank, efficient heat transfer increases the temperature of the water. The exhaust is cool, dry air.
Grahame specified an 80-gallon Voltex hybrid heat pump water heater for the application, locating it in a second-floor closet at the top of the stairs. A louvered door allows the Voltex unit’s high-capacity fan to draw in adequate make-up air for the unit. The cool exhaust air from the unit is vented into the insulated attic to help moderate the air temperature (especially in the warmer months) and control humidity, both of which affect indoor comfort. “I have a great deal of interest in how the heat pump water heater affects humidity,” he points out. Grahame installed numerous sensors in the slab, walls, and attic to monitor temperature and humidity.
The Voltex water heater will consume less than 5,000 BTUs per year for an average annual cost of $109, according to a recent certification of the home.
Bret Wagenhorst, a local optometrist and former member of the Tift County Foundation, recently purchased the Net Zero home. He has agreed to keep the building open for testing and to allow interested parties to tour the innovative home. To date, thousands of people have visited the project throughout the construction process, including building inspectors, construction and design professionals, government officials, and interested citizens have seen the Net Zero Energy house construction details and technologies first-hand. “This has truly been a community project,” Grahame points out.