Amber Wood, PE
August 30, 2012
Bound for Net Zero
Typically low energy is not desirable – except when it comes to buildings. According to the U.S. Energy Information Administration, buildings consumed about 42% of the energy in the United States in 2010. About 23% of the energy was used in homes. Almost one-third of the energy used in homes is for heating, cooling, and water heating. This makes a serious case for energy efficiency in residential buildings and leads to discussion of future goals for housing. With this, the logical focus quickly turns to net-zero energy homes.
Using building science principles, this goal seems pretty attainable. However, there are stumbling blocks even before you get to the science of this issue. One is that there are many different ways of talking about net-zero. Both the National Renewable Energy Laboratory (NREL) and the Net-Zero Energy Home Coalition have worked to define net-zero, and below are a handful of their related definitions:
- Energy-plus home: a home that produces more than it consumes annually
- Net-zero energy home (nZEH): a true nZEH produces as much as it consumes with zero net energy consumption and zero carbon emissions annually
- All-electric net-zero: a home that produces as much as it consumes with zero net energy consumption annually (but not zero carbon emissions)
- Near-zero energy home: a home that produces almost as much as it consumes annually
- Builder-installed electric net-zero: a home that produces enough to cover any builder-installed consumption annually (typically excluding miscellaneous electric loads and additional appliances)
- Net-zero energy ready: a home designed to produce as much as it consumes annually without renewables installed, but with pre-wiring in place for future installation of renewables
It is easy to see how this nuanced terminology can make the discussion of net-zero even more daunting than the science behind it. But despite the complex terminology, Home Innovation Research Labs has been working steadily with builder and remodeler partners on net-zero energy homes. We've developed a tried-and-true methodology for approaching net-zero. The first step is to design an efficient building enclosure, including air sealing and insulating the walls to reduce the loads for heating and cooling using the most affordable solution for the specific climate. Next, we help our partners investigate efficient equipment to heat, cool, and provide hot water as efficiently as possible. This includes bringing ducts within the conditioned space and addressing ventilation. The final step on the path to nZEH is adding renewable energy systems to the house.
So, does this straightforward three-step methodology really work? We have seen it work time and time again with our builder and remodeler partners, including Asdal Builders, John Wesley Miller Companies, the Lancaster County Career and Technology Center (LCCTC), Bob Ward Companies, and most recently Nexus Energy Homes. The projects have varied from an energy-plus home, to a near-zero energy community, and even remodeling to nZEH, but the same basic steps and principles have guided all these builders to their own net-zero successes.
But we all know there's more to these solutions than just the proper methodology – there's also the issue of cost. While in some cases there may be a premium for buying one of these houses, and therefore a larger mortgage, there is the potential for significant savings on utility bills. One homeowner frequently sends us his utility bills which average about $10/month – and more than half of that is the cost to simply stay connected to the grid! It’s a powerful combination when successful, efficient design becomes practical, affordable, and more mainstream.
We'd love to hear about your experiences with net-zero in your market – let us know if your methodology differs significantly from ours or if there are additional rules of the road you've learned from your net-zero journey. We're also always on the look out for more builder and remodeler partners to work with us on related projects for DOE's Building America and other clients.
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