High Quality, High Efficiency, Low Price?

With affordability in mind, the U.S. Department of Energy funds research that’s helping homebuilders to improve quality and reduce energy use without straining the homeowner’s wallet. As part of this research in affordable, quality homes, Oak Ridge National Laboratory (ORNL) collaborated with IBACOS to design “near-zero” energy homes for Habitat for Humanity in Oak Ridge, Tennessee.

Today, two low-income families in Oak Ridge each live in a solar-powered, high quality, highly efficient, 1,106-square foot home that was built and provided by Habitat for Humanity. There’s only one catch for the families. They allow ORNL to gather data on the use of energy in the homes for a research initiative by the U.S. Department of Energy called the Zero Energy Home.

The Zero-Energy Concept

A zero-energy home lights a chandelier, plays the stereo, and makes a pot of coffee using a home-scaled power source, such as photovoltaics or wind power. Although connected to a commercial power grid, the zero-energy home produces as much energy as it uses or more over the course of a year. While alternative energy sources, such as solar panels, are still pricey, they do drastically cut monthly energy bills for the homeowner. With the assistance of the U.S. Department of Energy and labs such as ORNL, the Zero Energy Home research initiative may one day make the technology behind a zero-energy home an affordable reality by researching new energy efficient design and construction, energy-saving appliances, and systems based on renewable energy.

Efficient Mechanicals

In order to conduct its research, ORNL designed the two homes for Habitat for Humanity with identical floor plans and orientation. This duplication creates a lab-like condition for comparing differing components in the home, such as the HVAC systems.

The mechanicals and ductwork of both homes reside in conditioned space, but that’s where the similarities of the systems end. In one house, ORNL and IBACOS designed an innovative, highly efficient heat pump water heater. In the winter, the system draws heat from air in the home’s crawl space, which is sealed and insulated with rigid foam on the top and sides so the natural warmth of the earth is put to use.

In the summer, it taps into the heat emitted from the running refrigerator, which in addition to being resourceful, helps to lighten the cooling load. In the second house, a high efficiency electrical unit produces heat for the home. The unit is a direct exchange (DX) ground source heat pump that finds heat below the surface using underground copper piping. This piping is unusual because refrigerant flows through it, instead of water, so it retains heat better. In both homes, the HVAC systems work less and conserve energy by making use of various sources of heat typically ignored in traditional homes.

In addition to the innovative HVAC systems, large photovoltaic panels on the rooftops convert sunlight into electrical capacity for the homes. The panels connect to a power grid, so the home can tap into the grid on a cloudy day and sell energy back to the power company on a sunny day when the panels generate excess electricity. Although a cleaner resource environmentally, solar power alone does not ensure efficiency. ORNL keeps the energy bills low by integrating construction methods that make a well-insulated, airtight house.

Low Energy Bills

Among the efficient methods of construction in the homes are the use of low-emissivity, double-paned windows, reflective paint on the metal roofs, and structural insulated panel systems (SIPS) for the walls and roof. Made up of a block of expanded polystyrene foam sandwiched between two structural layers, commonly ½-inch oriented strand board, SIPS insulate well and uniformly. They allow for more insulation and, when properly installed, make a home more airtight. Although specifications of the SIPS varied at each location, both homes were built using SIPS construction, with peel-and-stick flashing tape applied along the seams. Blower door tests, measuring airtightness, gave exceptional results at 1.15 ACH at 50 Pascals.

Affordable living?

While the costs to build the two homes in Oak Ridge were higher than a home built with traditional methods, the monthly upkeep is enticingly inexpensive and perfect for the low-income homeowners. The average daily cost of heating, cooling, and running the appliances in these homes falls under $1 per day, while a conventional home in the area costs between $4 to $5 per day. As an example of research at work, these new homes in Oak Ridge are helping to make the concept of the Zero Energy Home an affordable and efficient option.