Getting to Net Zero
published in the 2012 WNCGBC Directory
By Matthew Vande and Emily Boyd
Imagine living in a home that creates as much energy throughout the year as it uses. You could eliminate one of your largest sources of carbon emission and your power bill at the same time. The “net zero” movement is the pinnacle of the energy-efficiency movement, and a growing number of people in the Western North Carolina community are striving for it. We’re proud to be two of them.
When we say net zero we mean net-zero energy: a home that generates at least as much onsite renewable energy as it uses. Some people prefer to work toward net-zero carbon emission or net-zero energy cost. In most cases, the performance level is similar among these definitions, with the specifics of utility-rate structures and the mix of fuel sources used accounting for the differences. Regardless of
the precise terms, net-zero homes are high-performance
There are two ways to approach making a home net zero. The first is to think about strategies after a house has been
designed and/or built. Usually this approach requires a much larger renewable-energy system and the cost and physical size of the system can be difficult to absorb. Energy efficiency is still generally less expensive than renewable energy. It really helps to start with a deep-energy retrofit. A small home, or a relatively efficient home, offers the best chance of success.
The more cost-effective way to approach net zero is to identify it as a goal early in the project and design the home to use as little energy as possible. This makes the renewable-energy system required to achieve net zero much more manageable in terms of physical size and cost. We estimate that at least half of a typical new home’s energy use could be eliminated through energy-efficient design practices. The more a house takes advantage of these, the less renewable energy it will require.
Passive solar design is a great starting point for a net-zero building, and was used in at least half of the local net-zero homes that we know about. Why not take advantage of solar energy that you are already getting for free? If you are careful about how you orient the house, size the windows and south-facing overhangs (as well as the types of glass you use), and use thermal mass to store this free solar energy, you will
be well on your way to achieving a net-zero home.
It’s also important to keep this conditioned air inside the home. Insulation and air sealing are critical. A net-zero home should have wall, floor and roof insulation that exceed code. Too many windows can create a problem, since walls are much better insulated than glass. Sealing every crack in the building with caulk or foam is an important and cost-effective way to reduce air infiltration and humidity migration that can consume excessive energy. Ducts should be inside conditioned space to eliminate another potential route for unintended air exchange with the outdoors.
It’s crucial to have the home designed and inspected to make sure these goals are met.
Efficient heating and air-conditioning equipment also matters. Many local net-zero homes use ultra-efficient geothermal (ground source) heat pumps which provide both heat and air conditioning. Others choose to use solar hot water radiant systems with a gas backup, and may install
a very small air conditioning system. Some people choose not to install air conditioning, but it may be necessary for humidity control.
Water heaters are another area where efficiency is critical. The most efficient option is solar-water heating. For
all electric buildings, heat pump water heaters are more efficient than regular electric tank water heaters. For buildings that use gas, tank-free gas water heaters are an efficient option. Geothermal heat pumps can often provide hot water as a byproduct of heating and cooling when the units are in operation. This preheated water can be used to supplement the primary hot water source. Also, low-flow faucets, showerheads and ENERGY STAR appliances all use less hot water, which saves water and energy.
Efficient lighting options are also plentiful. Compact fluorescent light bulbs are inexpensive and easy to find. LED technology can be competitive with CFL lighting when considering lifetime costs. Using occupancy sensors, dimmers and timers can also reduce the energy that lighting consumes. Other electric loads can be reduced by purchasing ENERGY STAR appliances and electronics and
installing power strips with master on/off switches for things like entertainment units and office areas to reduce phantom
Once the building has been designed to be as efficient as possible, the remaining energy use must be offset with
renewable energy sources (typically photovoltaic, wind or micro hydro systems). The renewable energy is usually tied to the local electric utility’s “grid,” allowing the homeowner to buy electricity when the home needs more than it
produces and sell the excess when the home is producing more than is needed.
This approach has many advantages, including the elimination of costly batteries and contributing renewable energy to the grid during summer “peak power” times, when many utilities are generating its most costly and least efficient power. It will also make homeowners eligible
for some utility rebates and/or the ability to sell the renewable energy credits for their installation.
Both the federal and North Carolina governments have excellent financial incentives for renewable energy systems. In-state residents are able to get up to 65 percent back on
photovoltaic, solar thermal water heating, wind, micro-hydro and geothermal systems. The 35 percent N.C. state tax credit is available for passive solar material upgrades as well. Once these financial incentives are considered, the payback for each one can be quite short — often less than seven years.
Anyone setting out to build a net-zero home should enlist the help of experienced professionals early in the design phase because specific design elements will be different for every project. Wise decisions during the planning stage can save a lot of money later in both the construction of the home and the operating cost after it is completed.
Getting to net zero doesn’t have to be difficult or prohibitively expensive. With the current incentives available, there has never been a better time to try.
As we’re writing this article, we are sitting in the basement office of a passive-solar, net-zero home. The sun is shining in the south windows, the office desk lights aren’t needed, it’s a comfortable 72 degrees inside (even though it is 40 degrees outside), and the heating and cooling system hasn’t been
turned on in three months.
When we think of the fact that the only electricity being used in the office right now is the actual computer we are typing on, it just brings smiles to our face. Can’t you picture yourself in such a home? It’s easier (and less expensive) to create than you think.
Matthew Vande, an architect, and Emily Boyd, a general contractor, work for VandeMusser Design. VandeMusser Design provides technical consulting and certification services for green residential construction to builders, architects, developers, and homeowners in Western North Carolina. Both Matthew and Emily have recently completed their own passive solar, net-zero homes.