5:49 pm Feb. 14, 20121
A “net-zero” residence is a house, or a building, that produces as much energy as it uses.
It may sound like the sort of thing environmentalists or young architects like to talk about that's actually a distant goal, to be realized once the right technology comes along, or at least one that requires wealthy liberal clients who are willing to put their money where their mouths are.
But apparently, according to the speakers at a recent event at the Center for Architecture, none of this is true—as long as the occupants of net-zero structures are willing to play along.
“The real issue is the kind of miscellaneous loads—that thing that happens when people turn on TVs and computers and everything else they use in their house, and you, as an architect or designer, have absolutely nothing to do [with] the energy that goes into those miscellaneous loads,” said William Zoeller, an architect and senior vice president at Steven Winter Associates.
Zoeller was joined by James Garrison, founder of James Garrison Architects, and Matthew Bialecki, founder of Bialecki Architects. The lecture space at the Center for Architecture on LaGuardia Place was full, mostly with middle-aged people wearing sweaters and turtlenecks—a more think-tanky, less architect-looking crowd than the usual audiences there.
As it turns out, net-zero building is absolutely possible and has been done, using techniques and materials that are not particularly exotic.
The concept has already been put into practice outside academic or intellectual circles: The U.S. Army has a “Net Zero” pilot program, and one of three firms represented at the event was commissioned by the U.S. Customs and Border Patrol to study “high-performance” housing on the extreme north and south borders. A new block of housing for students at the University of California Davis, comprised of six buildings, is designed to be net-zero.
And though cost can be an issue, one of the firms represented at the event was hired not long ago to build an “affordable” net-zero development in northern Massachusetts and another project that involved 11 1,500-square-foot homes near Sacramento.
Net-zero building is not the same as “green” building. Reducing greenhouse gas emissions is a goal in green building, but energy is not the primary focus. Net-zero building does not necessarily concern itself with reducing waste, nor is the use of recycled materials necessarily a priority.
A net-zero building doesn’t really have any specs in that sense; it's simply the product of an equation: energy produced minus energy used equals zero.
The first half of that equation usually means solar power or wind power or, if the cost can be accommodated, geo-thermal. That’s not going to be nearly enough energy for today’s average household, so the second part of the equation, energy used, has to be addressed too.
The first thing to consider is what a house needs energy for: heating, cooling, appliances, lighting that is not provided by daylight, and hot water are the most basic needs. In terms of how to meet those needs using the least possible energy, that means thinking about the buildings’ “envelope”—the walls, roof, windows, basement and floor. Related, there's “super-insulation”: Before anything else, the house has to be as tightly insulated as possible so that any energy produced stays inside it.
“That is going to be the key to the whole thing,” Zoeller said.
Insulation may seem a bit basic to be the “key” to anything new, but saving energy through what the architects referred to as “passive” elements—those are the elements which, like insulation, work without using any energy—has not been a priority in building most houses in the last several decades.
To maximize the efficiency of the envelope, the building’s main spaces should be oriented to the south, where the sun provides the most natural light and heat and, if there are solar panels, energy. All the architects who spoke emphasized the use of triple-glazed windows as part of the envelope.
The roof is a somewhat different story, because there are times of year in which holding heat in the house is not the only goal; there is also ventilation to think about. In a net-zero home, the roof insulation is meant to keep heat out as much as it is to keep heat in, but Bialecki doesn’t think it’s enough, and believes that all net-zero houses should be outfitted with “radiant barriers,” which are more or less anything that prevents heat transfer, in this case from the roof down to the rest of the house. (A radiant barrier developed by NASA goes on the surface of spaceships to protect them from extreme termperatures.)
“A roof system in the summer, in the Hudson Valley, can easily get to 160 degrees and any insulation—I don’t care what you put up there—is going to fail eventually,” Bialecki said. “It’s heat transfer; it will go from there into your building. With a venting system, with a radiant barrier system, at least you’re just circulating the 90-degree air. It’s not 160. It’s a huge difference.”
No one spent a great deal of time on lighting and appliances, because the solution is really simple: L.E.D. lights or compact fluorescent light bulbs, and “Energy Star” designated appliances.
Domestic hot water, however, is, according to Zoeller, the next-largest energy load after heating. There is more than one way to address it, one being a solar-heated water tank, another being a heat-pump water heater, which takes excess heat from other sources in the house—appliances, for example—and transfers it, electrically, to water in a tank.
At one point Zoeller showed a graph of the energy use of each of the 11 houses in a net-zero project in Sacramento after a year. One was negative, several were very close to zero, one was markedly higher than all of them. (He suggested, presumably in jest, the possibility that it was a marijuana farm.) The median was about $400 in energy costs for the year.
“Obviously it’s the occupant you really can’t do anything about,” he said.
The architects showed the most passion when talking about air conditioning. Or in particular, about the wastefulness of it.
According to Garrison, air conditioning uses twice as much energy as heating a building. He said that there are ways that the house can be built that minimize the need for air conditioning at all, but that ultimately, as with an net-zero enterprise, it would be up to the client to make it work.
“The one thing we are really evangelical on is we do not air-condition our homes,” Bialecki said.
In a climate like that of New York, he said, "it’s ridiculous. You’ve got six to eight weeks at most of humidity and high temperature, and through proper orientation, proper building envelope design, you just don’t need it.”
Years ago, he said, he and his colleagues were making a presentation to prospective clients and “one said a very prophetic thing: ‘People will look back on the late 20th early 21st century with amazement that we felt that the air we breath was insufficient and we had to condition it and filter it in order to breathe it.”
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