Aiming for Zero: How to Build a Zero-Carbon Home

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Architect Jim Logan reflects on our energy future in front of a solar-powered home he designed in Colorado.
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Wild Sage Cohousing Apartment Complex faces north and south, which allows significant heat gain through southern windows in the winter.
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Habitat for Humanity House features a long axis that faces south, with enough windows to gain some passive solar heat.
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This American "dream" home is insulated and sealed with urethane foam in the roof, walls and basement.

A long-time environmentalist, Colorado-based architect Jim Logan has been building solar and low-energy homes since 1975. Feeling the growing need to combat global climate change, Logan now focuses exclusively on carbon-neutral buildings–those that release virtually no CO2 into the atmosphere. We asked him to talk with us about how regular people can reduce their homes’ carbon footprints to zero.

Q: How does a grid-connected, zero-carbon footprint house work?
A: A zero-carbon footprint house supplies more energy to the energy grid than it takes. The grid, in this case the public service company, is used as a storage device. We try to generate enough energy to run the building and produce some excess. On a bright sunny day when your solar panels make more energy than you can use, you can sell the excess back to the public service company. On cloudy days, you take power from the grid.

Q: Can any residence have a zero-carbon footprint?
A: Yes. The first step with any building–new construction or an existing building–is to do as many things as possible to lower the building’s energy consumption so less energy is required to power the building. This is often referred to as “reducing the load.” It’s possible to build super-efficient new homes fairly economically by using high levels of insulation and highquality windows. With existing construction, you can reduce loads by adding insulation wherever possible and by reducing air leaks.  Once you’ve reduced the load, it’s time to add some alternative energy system–in our case, solar thermal panels for hot water and/or photovoltaic panels to make electricity. You should implement conservation strategies such as increasing insulation and reducing energy use before investing in solar thermal and photovoltaics; it’s less expensive to buy light bulbs or add insulation than to buy and install more solar panels. Once you’ve done all you can to conserve, you may find you need fewer panels than you thought.

Q: Can you explain in more detail the difference between solar thermal panels and photovoltaics?
A: There are two basic types of solar panels. Solar thermal panels are used to heat water, whereas photovoltaics produce electricity for the home.  Solar thermal panels are composed of three parts: a solar thermal collector; a fluid system to move heat from the collector to its point of use; and a tank for heat storage. Solar thermal panels are particularly cost-effective for heating hot tubs and swimming pools, which require huge amounts of heat. In certain parts of the world, code requires that a substantial portion of your hot water be provided by solar. Israel has mandated solar heating systems since 1980, and Spain requires new and renovated buildings to obtain 30 to 70 percent of their hot water through solar power. Starting in 2010, Hawaii will be the first state to mandate installation of solar water heaters on new homes.  The most widely available photovoltaics (PVs) are thin strips of silicon, sliced up and glued onto glass, which generate electricity when the sun shines on them. One of the great things about PVs is that their life span appears to be indefinite. We see no dropoffs in their production after 20 or 30 years, so they will likely make electricity forever.

Q: Based on current energy costs, how much would it cost to install PVs on a 2,500-square-foot house?
A: Let’s assume you have tidied up your energy consumption by getting an Energy Star refrigerator, replacing all your light bulbs with compact fluorescents, and turning off your TV and cable box with a plug strip so they aren’t running all the time. A 3-kilowatt (or 3,000-watt) system will handle the needs of most families; the national price of PV is currently about $9 per watt. If you live in a state that offers rebates, the cost would be about $12,000, installed.

Q: What kind of cost savings could be realized?
A: We’ve seen the cost of these systems drop about 5 percent a year, so it’s continuing to cost less to install them. In states like Colorado, New Jersey, New York, California and Florida, where homeowners get rebates from the energy company as well as tax breaks from the government, a system will pay for itself at the current utility rate in about seven years. It’s difficult to say what future electrical rates will be, but once you buy PVs you’ve essentially paid for all of your home’s electricity until the end of time.

Q: How effective are PVs in parts of the country that get less sunshine?
A: The work pretty well even in cloudy climates, but what really changes as you move from one part of the country to another is the heating and cooling loads. For example, Texas and Arizona are cooling-dominated climates with a large need for electricity in the summer. This can be mitigated by using evaporative coolers instead of air conditioners, which is a good example of using conservation techniques to eliminate the need for additional supply.

Q: Is it possible to become carbon neutral without installing PVs?
A: Yes, if you have an all-electric house and your utility company allows you to sign up for non-fossil-fueled energy, such as from wind, hydropower or geothermal energy, you would be carbon neutral and it would be cheaper than installing PVs. But that would also require a vast majority of us signing up for renewable power through our local utilities to create the demand for more wind turbines. There are also wind and geothermal systems for the home.

Q: If everyone does his/her part, can we really have a positive cumulative effect on global warming?
A: I believe we can and must reduce the carbon emissions in the United States by 80 percent in the next 15 to 20 years and it’s going to take a tremendous effort to do so. The problem is that each of our individual actions seems so miniscule compared with the overall amount of CO2 going into the atmosphere.  But when large masses of people participate, it absolutely makes a difference.

Energy-Saving Incentives Coming Soon to a City Near You

For the past year the Boulder Energy Project has been gathering data to determine how much it would cost to convert all Boulder, Colorado, residences to zero-carbon emissions buildings by 2030. The hope is that residents will be able to borrow money for photovoltaics or Energy Star appliances and pay back those loans using the dollars they save on their utility bills.

“If the community or the energy company can provide low-interest loans to pay for the reduction in energy use, things like appliances will pay back in three years or less,” says architect Jim Logan, who is collaborating on the groundbreaking project with several groups including the City of Boulder, the Center for Resource Conservation and the National Renewable Energy Laboratory. “You could end up with a new refrigerator and reduced utility bills.”

Boulder is not alone in its race to reduce carbon emmissions.  PNM, New Mexico’s public utility company, started a refrigerator recycling program offering free pickup and a $30 rebate for old fridges. The company claims getting rid of that second inefficient fridge, which people tend to keep running in the garage, can save an estimated $100 annually.  Other programs include a $500 rebate for builders who construct Energy Star-certified homes, a free program for low-income customers to install energy-saving measures in their homes, and a rebate program for customers who use energy-efficient evaporative coolers. In Berkeley, California, building codes for new homes, renovations and sold homes must comply with Residential Energy Conservation Ordinance (RECO) standards to further the city’s goal of reducing greenhouse emissions by 80 percent by the year 2050.

According to the Database of State Incentives for Renewables & Efficiency (DSIRE), a project funded by the U.S.  Department of Energy, 15 states offer both state and utility energy rebate programs.  Visit www.dsireusa.org to find out about tax incentive programs in your city or state. 

Stop Global Warming: 3 Things You Can Do Right Now

Architect Jim Logan urges simple actions that require minimal effort.

1. Change all your light bulbs to compact fluorescents.  “It will save you two-thirds on energy costs, cut your carbon emissions for lighting by two-thirds and save you a lot of money over the life of the bulbs,” Logan says. He recommends bulbs with a color temperature of 3,500 for a warm glow. “And if you’re concerned about recycling compact fluorescents, Home Depot has a recycling program.”

2. Reduce your plug loads. Most people aren’t aware that their TVs, computers and cable boxes, even if they are turned off, keep running and can literally use as much electricity as a refrigerator while in standby mode.  The solution is as simple as plugging those items into a power strip that, when turned off, totally cuts power to the appliances.  “That way when you’re asleep or at work, it’s not costing you money and it’s not costing the planet CO2 emissions,” Logan says.

3. Find an audit or weatherization contractor. A one-day audit measures things like how much air blows through your house and offers solutions for adding insulation, caulking and sealing windows and doors, and using weather-stripping.  “It’s not uncommon in an older, poorly constructed home to save half the heating energy with a simple one-day weatherization, insulation, and caulk and seal,” Logan says. “Your local utility company is a good resource for finding someone to perform this service, or go to the Energy Star website and look for information on home audits.” 

Getting to Zero:  Efficient Building Projects Come In a Range of Styles.

Wild Sage Cohousing Apartment Complex
Boulder, Colorado
Apartment systems are inherently more efficient than single-family homes, partly because of size–these units are 800 to 1,600 square feet–and partly because of shared resources. In this case, shared sidewalls and a common hydronic heating system reduce heat loss and minimize mechanical redundancy. The buildings face north and south, which allows significant heat gain through southern windows in winter. Minimal west-facing windows help avoid summer heat gain.  Solar collectors warm a shared hot water tank. Walls are insulated with standard blown cellulose, roofs with fiberglass batt and windows with double low-E coatings.  These innovations, along with conservation, mean residents use about 300 kilowatt hours (kwh) per unit per month, compared with 700 kwh or more for an average family (2.6 people).

Habitat for Humanity House
Wheat Ridge, Colorado
The National Renewable Energy Laboratory in Golden,
Colorado, sponsored this 1,200-square-foot home for
Habitat for Humanity, seeking a building system that
was cost-effective, replicable and familiar to Habitat for Humanity’s volunteer builders. The simple design features a long axis that faces south, with enough windows to gain some passive solar heat. The project formed a snug envelope using standard construction techniques, packing the double-stud walls (two walls set an inch apart are both filled with insulation), the floor and the roof with typical fiberglass batts. Low-E windows reduce heat loss, and two solar collectors on the roof supply hot water. An efficient natural gas heater warms the main space, while bedrooms are warmed by 4 kilowatts of photovoltaics on the roof. In its first year, with the help of its energy-conscious inhabitants, the house distinguished itself as a net energy producer.

American “Dream” Home
Boulder, Colorado
This 3,950-square-foot (including basement) classic American home is insulated and sealed with urethane foam in the roof, walls and basement. Double-pane low-E windows further limit heat loss. An efficient natural gas boiler supplies hot water for domestic use and for the radiant floor system. An evaporative cooler, which replaces air conditioning, minimizes summer electric loads. The occupants could easily have lower-than-average energy bills and carbon emissions. But because they use large amounts of electricity and hot water, their consumption habits keep energy bills high and bring them close to the national average (around 39,000 pounds of CO2 emissions a year). User behavior is as important to green building as the building itself.  A low-energy house is just one part of a low-energy lifestyle.

Published on Nov 26, 2008

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