The Green Column #11
Net Zero Houses Buffer Rising Energy Prices
September 21, 2009— Life is full of surprises. Americans have had their share over the last year. The economy remains shaky and unemployment is increasing. However, one thing is certain: the price of energy will continue to rise.
Two ways to combat rising energy prices are to use less and to produce your own. Owners of net zero homes are doing just that and saving money every month while reducing their anxiety about the future.
“Net zero” is a new term and used in several ways. The “zero” may refer to energy use, energy cost or carbon emissions. In the U.S., common usage applies to energy cost, while in Europe emissions are usually the standard.
In either case, the idea is to build a house that is super insulated because it is much easier to save energy than to produce it. Then a source of renewable energy is added sized to equal or exceed the electricity, natural gas or other energy imported to the site. This could be solar panels on the roof but also a wind generator or even a hydro unit in the right location.
(Technically, “net zero” is a misnomer. All manufactured and processed materials and the appliances, furniture, and equipment and systems required to make and furnish a home use energy to harvest, manufacture and transport to a site.)
European countries have taken the lead in requiring new homes to use only clean energy and have zero net carbon emissions.
The United Kingdom mandates that all new homes be zero carbon by 2016. France and Germany are debating stronger building requirements of their own. And Denmark will require all new houses to meet the “passive house” standard by 2020, meaning using 85 percent less energy and producing 95 percent less carbon dioxide than regular houses.
The U.S. is lagging behind with only about 100 net zero energy houses occupied nationally. Locally, so far we only have one net zero energy home, at “The Bridges” southwest of Lincoln (S.W. 27th and W. Denton Road), built by Rezac Construction.
A net zero house begins with well considered green design and air-tight construction and excellent insulation ranging from R-25 walls to R-60 roof. The Rezac house is oriented to the sun for maximum solar gain during the during the cold months while shading windows from the hot summer sun.
Energy efficiency involves every system in the house and their interactions. The key to a healthy and air-tight home is having all the systems balanced. All openings such as electrical boxes, light cans and sump pumps are urethane foam sealed.
With the house tightly sealed, an energy recovery ventilation system is installed. These ventilation systems recapture heat from the exhaust air and they can help to maintain humidity at proper levels. Filtration systems remove pollen and allergens keeping the air cleaner than in a typical house, which can have indoor air that is five times as polluted as outside air.
Other energy efficient features of the net zero house are:
- Energy efficient lighting
- Energy Star appliances
- Sealed combustion gas fireplace or sealed wood-burning fireplace or stove with outside combustion air
- Exterior air infiltration barrier
- Photocell controlled exterior lighting
- High efficiency windows and doors
“The Bridges” net zero house also uses recycled materials:
- Locally quarried stone
- Carpets made of recycled material
- Wall board—gypsum with 100% recycled paper facings
To produce its own energy, the Rezac net zero house uses 40 photovoltaic panels. Surplus electricity produced by the solar panels can be fed back into the electrical grid through a process called net metering. Net metering is arranged in coordination with the local electric utility and has only recently become possible through changes in Nebraska law.
Additional energy savings estimated at $2,000 annually are gained through the use of a highly efficient geothermal heat pump. The house at “The Bridges” uses a stainless steel heat exchanger that is submerged in a nearby pond which pulls heat from the pond water for heating and dumps heat to the pond water for cooling. In the summertime, excess heat is also used to warm water for the domestic hot water system.
A net zero designed house in Omaha, currently under construction, uses a well-based geothermal heat pump system for its heating and cooling.
Many of these techniques are being adopted by the most innovative and advanced homebuilders. Air-tight design, super insulation and highly efficient doors and windows are features being demanded by homebuyers who are concerned about comfort and indoor air quality as well as energy efficiency.
Mike Rezac, chairman of the Nebraska Green Building Council, said “The Bridges” house, which he calls the Madison, is priced in the low $600,000s, but that innovation always costs more before familiarity lowers costs.
The project was funded by a $500,000 Nebraska Energy Office grant and the house is being used as a demonstration project for green building.
Because of the many overlapping incentives, subsidies and tax breaks offered in the home energy field, it is difficult to generalize about monetary payback periods for net zero homes. But it is safe to say that rising energy prices will shorten those times substantially. And no one can put a price on the satisfaction of lessening one’s emission of greenhouse gases.
It is estimated that Rezac’s house each year will reduce emissions by 22,781 pounds of carbon dioxide, 109 pounds of sulfur dioxide and 69 pounds of nitrogen oxide. That’s the equivalent of taking two cars off the road or planting 750 trees.
© Lincoln Green by Design