(This is the second of a two-part series on zero energy houses)
“Houses are polluters and big houses pollute more,” said Department of Energy Assistant Secretary David Garman in a recent interview. Elaborating on this startling piece of information, Garman said that houses are more accurately characterized as “indirect polluters.” That is, they consume 36 percent of the nation’s electricity, and 69 percent of that electricity is produced by fossil-fueled generating plants that collectively cause more air pollution than automobiles.
Clearly a man on a mission, Garman is now leading the Department of Energy’s (DOE) charge to build houses that use less electricity and therefore reduce–indirectly, of course–air pollution and greenhouse gas emissions.
In the past, DOE has encouraged home builders to build houses that use less energy for heating, cooling and hot water, which account for about 60 percent of the total in the average house, and which can be a mixture of gas, oil and electricity.
Now DOE has set its sights on the other 40 percent, which is almost entirely that indirectly polluting electricity. Lighting accounts for about 6 percent of the total; major appliances are 17 percent; and “plug load”–smaller appliances such as computers, televisions, and cell phone battery chargers to name a few–are another 17 percent.
Not only does DOE want new houses to use less electricity and less energy overall, it wants these same houses to have the capacity to generate clean electricity for their own use and to send any excess to the grid for use by other households.
This may sound a bit like chasing windmills, but when enough houses within a utility’s service territory can do this, the utility can meet its summer peak load without having to build additional, far-more-polluting peak-load plants. Another startling statistic–during summer peak loads, 60 to 70 percent of all electricity produced in the country is used to air condition homes and commercial buildings.
“Clean electricity” can be generated with wind or water, but you must live near a fast moving stream or in a place with constant wind. Photovoltaic cells on your roof that convert sunlight into electricity, however, can be done almost anywhere, and DOE regards them as a more practical solution.
To get this ball rolling and home builders interested, DOE set up its Zero Energy House (ZEH) program. A true ZEH is self-sufficient, generating all the energy that its occupants need. This can be done, but it’s far too narrow a market to capture the interest of any large-scale production builder. Instead, DOE’s scaled-down ZEH is one with 50 percent lower utility bills, compared to a new house of similar size built to a conventional standard in the same market. Cutting the utility bill by half, on average, also cuts the energy consumption by half, said Rob Hammon, a Stockton, Calif., engineering consultant who has worked with a number of DOE’s ZEH builders.
Halving the total energy consumption is still a daunting challenge, however. The easiest way is by excision–simply pull the plug on half the stuff in your house, take cold showers, set the thermostat to the far side of comfort, and air dry your clothes. A more realistic and saleable approach is to cut energy from each “energy sector” in the typical house. Using this approach to get the energy consumption down to DOE’s ZEH level, however, requires a joint effort from both the buyer and the builder
The builder can deliver the goods on heating, cooling, hot water and, where applicable, Energy Star appliances (some builders include appliances in a new-home purchase and some do not). The buyers will have to pick up the ball with the major appliances that the builder doesn’t include, and use energy-efficient lighting. To increase their energy efficiency even further, the buyers can also purchase more efficient small appliances.
A custom builder who works with larger lots can orient the house to the south so that the free winter sun can help heat the interior living spaces. Production builders working with ever-shrinking suburban lots, however, rarely have this opportunity. Instead, their efforts have centered on the house itself and focused on cutting heat gain (heat coming into the house), heat loss (heat going out of the house) and air infiltration (air coming in from outside that must be heated or cooled).
Air leakage and unpleasant drafts in cold weather can be cut by making the building envelope tighter and plugging up the air leaks that commonly occur around plumbing pipes and electrical outlet and switch boxes where standard batt-type insulation does not fit tightly.
To cut the heat gain or loss through the exterior walls, ZEH builders in both hot and cold climates will have to ramp up the insulation, often by as much as 50 percent.
In areas where the summer sun really beats down–notably across the southern tier of the country–the builder must also deal with radiant heat, which generally pours in through the roof and windows. He can reduce it with light-colored exterior walls and roofing material, radiant barriers (roof sheathing with aluminum sheeting laminated to its underside), and windows with low-e glass and a low solar heat gain coefficient (SHGC). The windows may sound exotic, but most window manufacturers make them. A side benefit of a low SHGC: your furniture won’t fade as much.
The last bit for heating and cooling is the mechanical equipment. With all these modifications to the building envelope, your builder will have cut the heat gain and heat loss to such an extent that a smaller-sized furnace and air conditioner will suffice. They will use less energy than the standard size for your house, but the builder can wring out even more with a high-efficiency furnace and air conditioner.
Another area where the builder can boost energy savings is with the hot-water heater. These can be energy hogs, whether you indulge in long, hot showers or not because much of the energy consumed by the hot-water heater occurs when it is in standby mode. By contrast, a tankless hot water heater works on a demand basis, only heating water as it is needed. A ZEH builder may also offer a solar hot-water heater, but you will still need a tankless one as backup for those cloudy days.
The builder’s last act will be installing the PVs on the roof. In DOE’s ZEH program, the PVs may produce 60 percent to as much as 100 percent of the household’s electricity needs.
About this time, you may be asking, how much do you have to shell out before you can enjoy such energy efficiency?
The most expensive single item will be the PVs, but their actual cost depends on where you are buying them; some states and local utilities will subsidize as much as 50 percent of the purchase and installation costs. Without the subsidy, the cost averages about $8 to $10 a watt. A 2-kilowatt system that a ZEH home builder might install on a 2,400-square-foot house would run about $16,000 to $20,000 But, in California where local utilities may offer the 50 percent subsidy and homeowners get a 7.5 percent state tax credit, the cost is about $7,400 to $9,250.
Homeowners whose local utility offers time-of-use rates will also save money. They can sell their surplus electricity to the grid during the peak daylight hours and buy it back during the off-peak night hours. Because of the difference in day and night rates, some ZEH California homeowners, for example, may save close to 100 percent of their electric bills over the course of a year, even though the PVs on the roof may only supplying about 60 percent of their electricity needs.
The cost of the building upgrades required will vary, depending on the climate where you are building. California, where the cost of electricity is high and a generous rebate for the PVs is widely available, has the largest number of home builders participating in DOE’s ZEH program. Centex Homes, Morrison Homes, Clarum Homes–all current participants–said that the cost of the upgrades and the PVs for a 2,400-square-foot, single-family house averaged about $18,000 to $20,000. With Centex and Morrison Homes, the ZEH features are optional. Clarum includes them in its standard house.
How have buyers responded to the ZEH program? Clarum President John Suppes candidly observed that ZEH did not top the list for his buyers at the time of purchase, but the features have clearly been a big hit. “A year after they moved in,” he said, “all they want to talk about is their Zero Energy House.”
Quotes or Queries? Katherine Salant can be contacted at www.katherinesalant.com.
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