A Home That Heats and Cools Itself
From The New York Times
By David Pogue
This week, on my blog, I’ve been writing about the inventions I saw at last week’s Modern Marvels/Invent Now finals. About 25,000 inventors from all walks of life entered this annual contest, which is run by the History Channel and the National Inventors Hall of Fame. I was among the six judges who were asked to declare a winner from among the 25 finalists still standing.
The grand prize ($25,000) went to something called the Enertia house, which was invented by an engineer and former log-home architect, Michael Sykes. It’s a design for a home that heats and cools itself, with benefits both the homeowner and the environment.
Two factors contribute to this effect. First, the entire house is made of southern yellow pine. According to Mr. Sykes, this wood is especially efficient at maintaining a constant temperature; it absorbs heat during the day and releases it at night.
Second, air circulates in a convection cycle from top to bottom of the house, constantly redistributing the heat.
Mr. Sykes, who has built 80 of these homes, says that he was inspired by the way the earth’s own atmosphere keeps the planet at a relatively constant comfortable temperature despite the frigidity of space. It occurred to him that a house could have its own atmosphere, which might work the same way. As a side benefit, he says, one Enertia house has an environmental impact akin to taking 50 cars off the road.
After his victory, I interviewed Mr. Sykes by e-mail.
DP: What is the “sunspace?” It looks like a sort of windowed atrium the full height of the house, but how does it play into the envelope concept?
MSS: The sunspace is always on the south, or the side that’s within 35 degrees of south. It connects to the attic, which connects to the space between the double north walls, which connects to the basement. There are metal grilles in the sunspace floor to complete the convection loop.
The space in the north double wall is also a great place to put pipes and wires, which would otherwise be a problem, since the walls are solid glulams [glued wooden blocks].
DP: How did you get into this? Where did you pick up all the science?
MS: I built houses to pay my way through engineering school, and I was asked to build a log house for a friend. We used the resinous local southern yellow pine; everybody else used white pine or cedar, which are lighter. To my amazement, it was more energy-efficient than anything I had built — but it was getting too hot on the sunspace side. I could have put in ducts and fans to move the heat, but that takes energy.
At the Equator, the sun creates what’s called a Hadley cell; the weather equalizes temperatures, rushing warmth to the polar regions. What I needed was a Hadley cell [for the house], and that required an atmosphere. The house already had a sunspace, an attic, and a basement; simply add a space in the north wall, and you have an atmosphere. Short-wave sun comes in, but long-wave heat energy cannot get back out. It’s like the greenhouse effect that warms the earth, but in miniature.
We started building houses, one by one. I would design, draw, and chart them. Emily, my partner, would cut and number the wood blocks (she listed her occupation as “homemaker”). Each one was tweaked, better than he last.
DP: Which part of the system does your patent protect?
MS: The patent is on a process to enhance the energy storage of the wood by seeding the natural resin with crystals to enhance the phase-change effect [from liquid to solid as the temperature changes].
Interestingly, resin is a waste product of the paper-making industry, and most paper mills would pay us to take it. But we don’t have the equipment to do this yet, so for now, we seek out lumber that’s dense with resin, and grown on clay soils from which the trees take up minerals. There is plenty of this in the South.
DP: Does geothermal energy play a part in the Enertia system?
MS: It plays the biggest part in the summer: the convection effect draws air from the cooler basement. But even in the winter, it plays a part: the 55-degree earth tempers the house’s atmosphere (the envelope) because the sun only has to raise the temperature from 55 degrees, not -30 or whatever the outside temperature is. The interior shell will never freeze, and pipes are protected.
DP: On your Web site, you say that these homes are *not* sealed up tightly, which is the usual approach to insulating, but that the constant airflow helps them “breathe.” Is that why, in the photos on your Web site, none of the homes are painted? Because that would stop the “breathing”?
MS: You can stain the house, but you should not paint it, for that reason. There are opaque stains that offer all the colors of paint if you want to do that, but a lot of clients just like the [all-wood] look.
DP: Is there any insulation, vapor barrier, sheeting, or drywall in these homes?
MS: There is no traditional insulation in the walls, because the wood, because of its cells, is insulative. There is traditional insulation in the roof, the inner shell floor, the inner shell ceiling, and around the foundation. There is a vapor barrier in the inner shell ceiling. There can be drywall on the interior, and in the partition walls that divide up the rooms in the inner shell.
DP: If these homes are self-heating and self-cooling, why do they also have heating and cooling systems?
MS: Most banks won’t give you a mortgage unless you have at least a minimal heating system, even in the Western states where the sun shines so much that some homes could do without.
Only the houses in hot humid climates have AC, and it’s for dehumidifying more than cooling.
DP: What do the critics say?
Two questions always come up. First, there is a group that thinks using wood for houses is bad for the environment — that using trees for any reason is bad.
Actually, nothing could be further from the truth. Wood is the only structural building material that is renewed on a scale vast enough to assure there will always be more than needed. And all of our wood comes from tree farms. No virgin wood was harmed to build this house!
There is also a large group that thinks that using wood for energy is good only if you burn the wood or distill it into ethanol or biodiesel. Again, nothing could be further from the truth; when you burn the wood, or wood-distilled liquid or gas, you release the carbon dioxide again.
Second, I often hear: “Concrete, brick, and stone are better for storing heat energy.”
They do store energy — but only *specific* energy, which means that as energy is put into the stone, brick, or concrete, the materials get hotter. While wood stores some specific energy, it also stores latent energy, which means the temperature is constant while the wood resins, lignins and cellulose goes through a phase-change. Luckily, that temperature is around 70 degrees F. In a house, you want the temperature to be constant.
DP: What will you do with your prize winnings?
MS: The guy you saw following me around, Frank Weller, is a documentary filmmaker. He has filmed us for five years, and is pitching his film to “Nova” and similar venues. Broke like us, of course. So we’re going to use the $25K to finish the film and take it to PBS.
We all think this is a major, clean solution to a major world problem, or we would not have stuck with it for 25 years. The sooner people learn about it, the better. Let’s see where it takes us.