An energy-efficient home is about more than expensive photovoltaic panels and wind turbines. Zero-energy homes produce as much energy as they consume, and these exciting abodes are redefining what it means to build green.
The following is an excerpt from Toward a Zero Energy Home by David Johnston and Scott Gibson (The Taunton Press, 2010). This comprehensive home energy self-sufficiency guide explores the design of zero-energy, near-zero-energy, off-the-grid and carbon-neutral homes from start to finish, giving readers an unparalleled look at these emerging trends in environmentally friendly building. This excerpt is from the Introduction, “The Case for Zero Energy Houses.”
The petroleum economy bared its teeth in 2008, and it wasn’t pretty. In mid-July, the cost of a barrel of crude oil reached an all-time high of $147, a 50 percent increase in just seven months and a threefold jump in three years. A few months later, as the world economy took a nosedive, prices dropped to less than $60 a barrel and gas prices dipped to nearly $2 a gallon. Heating oil customers in the Northeast who had locked in a winter’s worth of fuel at more than $4.70 a gallon looked wistfully at a cash price of less than $2.20. It was the most recent upheaval in our fossil fuel economy, and it almost certainly won’t be the last.
The cost of oil has a huge impact on every corner of the economy, in part because we continue to use so much of the stuff. Americans manage to burn more than 20 million barrels of petroleum products a day. About 12 million barrels of that is imported, making us the world’s largest consumer. Until a few years ago, that didn’t seem to matter. Oil was relatively cheap, and the Arab oil embargo of the 1970s was long forgotten. Now it matters a great deal as the developing world competes for a bigger share of this limited resource.
All of this affects how much we pay for energy. But the cost of fuel oil or gasoline looks like small potatoes in comparison with the environmental consequences of burning the enormous quantities of oil, natural gas and coal we pull from the Earth. Climatologists link an increase in atmospheric greenhouse gases to a steady rise in average global temperatures and a variety of climate changes, some of which may prove catastrophic. Carbon dioxide — a byproduct of burning hydrocarbons — is an especially noticeable culprit. Glaciers are melting. Weather patterns are changing, bringing bigger, more frequent storms to some regions and droughts and high temperatures to others. High energy costs and a lack of potable water could make some parts of the globe very difficult places to live in the future. Worse, climate changes are occurring faster than scientists had predicted only a few years ago.
What does building houses have to do with any of this? A lot. According to the National Renewable Energy Laboratory, 40 percent of all primary energy consumed in the United States and 70 percent of the electricity produced by U.S. power plants goes directly to commercial and residential buildings. By some estimates, buildings are responsible for 48 percent of the carbon released into the atmosphere.
This is where sustainable building first found a toehold. Using less energy for heating and cooling makes houses less expensive to live in while reducing their environmental impact. Other fundamentals of green building help buildings last longer, give them healthier interiors, and helped reduce the natural resources needed to construct them. People got it. Green building has prospered. As we write this, green building is just about the only good news in the building industry.
The question is whether these gains will be good enough in a world where oil can cost $100 a barrel in January and $147 in July. There are other issues: How much will fossil fuels cost over the life of a house? How do we keep housing affordable on a monthly basis if utility bills approach the cost of the mortgage?
Net-zero and near-net-zero homes take the goals of sustainable building one step further. But just what is a zero-energy house?
Not too long ago, a house that used 60 percent less energy than one built to code was called a near-zero house. That was quite an accomplishment. A house that was this energy efficient could be constructed mostly with conventional materials and techniques but with more attention to details, such as air sealing and insulation. Builders and architects got to thinking that going way beyond code may give them a market advantage.
Today, building standards are getting tougher, and there are many labels for super-efficiency. There are zero-energy homes, net-zero homes, carbon-neutral homes, and off-the-grid homes. What are we talking about here?
The simple definition is that a net-zero-energy building produces as much energy as it uses on an annual basis. This includes energy for heating, cooling and all the devices that plug into the wall. Net-zero houses are typically connected to a local electric utility. They use the grid for storing excess electricity generated by photovoltaic panels or a wind turbine, banking electricity at times of plenty and drawing on the surplus when production falls.
A house in a cold climate may need more energy than it makes during the winter but then makes up for it in summer when demand is lower and the photovoltaic system is running at full tilt. The opposite may be true in the South, where high humidity in the summer requires more electricity for air conditioning during peak months. But on average, zero-energy houses produce enough energy to offset the high-load months.
Most grid-tied homes are built where the local utility offers net metering. That means the utility will buy electricity at the same price it charges, but usually only until the net is zero. If houses produce more than that, the utility may buy it back. If so, it is often at the wholesale price, which can be as little as 1 or 2 cents per kilowatt hour when the retail price is 10 or 12 cents per kilowatt hour. That makes those excess electrons produced very expensive. In Germany, the government has imposed rates on utilities, forcing them to pay roughly 50 cents per kilowatt hour as an incentive to building owners to produce more electricity than they use.
Off-the-grid houses must provide all the electrical energy their occupants need, summer and winter. Other than relatively small battery banks, there is no place to store energy. The house is truly self-sufficient. For decades, a handful of builders around the country have experimented with off-the-grid approaches in different climates. They have taken very diverse paths to get to the end goal. Most often what makes the house self-reliant are changes in lifestyle for the families that live in them. Electricity goes on a budget. There is a fixed amount of energy available for any given day. If someone wants to take a hot shower, it has to be on a day with plenty of sun. If you want toast in the morning, maybe you can’t use the hair dryer. Most Americans aren’t willing to adjust their lifestyles that radically.
Houses can also be designed to produce enough energy to offset the embodied energy in all the building materials plus the energy required to build the house. This means the house must produce more energy than it uses on a yearly basis. Roughly 8 percent of a home’s energy use is embodied energy from producing and transporting the building materials used in its construction. This is sometimes called regenerative architecture, and it has a deep ethical vein running through it.
A carbon-neutral home uses a different metric to determine how to get to zero. More than just zero energy, it must be zero carbon emissions all the way back to the power plant or manufacturing facility that made the building products in the first place. On average, getting electricity from a power plant to a house is at best 30 percent efficient. From a carbon-neutral standpoint, the electricity used from the grid has to be repaid with three times more site-generated electricity to break even. The same holds true for building materials. If the marble tile in the foyer is from Italy, the energy produced at the house has to be sufficient to make up for the embodied energy from extraction and transportation of the marble. The utility buyback policy also dictates the financial context for this approach. Adherents to carbon-neutral houses are insistent on using only local materials and simple solutions to getting to zero energy. The more complex the house, the more diverse the sources of the materials and the more energy needs to be produced.
Size also comes into the net-zero discussion. Some say a 10,000-square-foot home can never be sustainable — it is just too big and energy- and material-intensive. How can a family of four need so much space when in developing countries 10 families would inhabit a house that size? Communities such as Marin County in California and Aspen in Colorado penalize houses that exceed a prescribed maximum square footage. The larger the house, the more energy efficient it must be until finally, at a certain size, code drives the design. Aspen allows a homeowner to buy his or her way out of this problem by putting money into a fund that pays for solar collectors on homes of police officers, firemen and teachers. The result in net carbon may be the same in this Robin Hood approach to reducing carbon emissions.
But let’s keep it simple. For our purposes, net-zero or zero-energy means the house makes as much energy as it uses over the course of a year.
Regardless of the term we use, builders are realizing opportunity in this upside-down market by building homes that provide financial security for their customers. By minimizing utility bills or even creating the potential for the home to make money by selling energy to the utility at some point in the future, zero-energy homes offer a new direction for housing in America. It is a win for the homeowner, for the planet in aggregate, and for a new generation of builders who will be able to construct houses that better meet future energy challenges.
Building a real net-zero house is more than investing an arm and a leg in photovoltaic panels or buying a big wind generator. Reducing the amount of energy needed to heat and cool the house is the essential consideration, and that means a tight, well-insulated building envelope and more awareness on the part of homeowners about their energy use. Investing in energy-efficient appliances and lighting fixtures, eliminating phantom electrical loads, and orienting the house to take advantage of sunlight all cut the demand for electricity and fossil fuels.
But even taking all of these steps won’t necessarily get a house all the way to the land of net zero. Much more realistic are near-net-zero homes. These houses are also designed to drastically reduce the amount of energy they use, but they fall somewhat short of producing all the power they use. Many of the builders of these homes talk about the 80/20 rule: Eighty percent of the load reduction can cost only 20 percent more than a standard house, but the last 20 percent can mean an additional 80 percent of the incremental cost. This is hardly a failure. What if all new houses in the United States used 90 percent less energy than what we use now? Even 80 percent less? The impact would be immense.
There are scores of builders all over the United States and Canada who are constructing houses like these. A general public clamor for better energy performance has helped, and so have a variety of public and private programs that promote zero-energy construction. In Massachusetts, there is the governor’s Zero Net Energy Buildings Task Force, announced at the Northeast Sustainable Energy Association’s 2008 building energy conference. Architecture 2030, created by architect Edward Mazria, is pressing for changes in building design and construction that will make all buildings in the United States carbon neutral by 2030. The U.S. Department of Energy, the Canada Mortgage and Housing Corporation, the California Energy Commission and a variety of other public agencies have launched their own initiatives.
Building a net-zero house can get expensive, but it doesn’t necessarily have to be. In New York City, for example, architect Chris Benedict specializes in multifamily buildings that use a fraction of the energy that a conventional building of the same size would consume. Benedict is able to accomplish this without the use of any renewable energy systems and at a cost no greater than conventional construction. A net-zero Habitat for Humanity house near Denver was built for $116 a square foot. Near-net-zero houses built under the Habitat program in Tennessee have energy costs of about $1 per day — it’s not just a game for the well-heeled.
There is no single path toward energy self-sufficiency, nor are we arguing that building net-zero houses will magically solve the world’s energy or climate problems. But one house at a time, one neighborhood at a time, is how green building became mainstream. Building houses that are energy self-sufficient is completely within our capabilities — not at some distant point in time, but right now.
Reprinted with permission from Toward a Zero Energy Home, published by The Taunton Press, 2010.
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