Solar Suburbs
We attended two days of the Solar Decathlon in 2007. Held roughly every two years on the National Mall, twenty university teams attempt to build a small, efficient house that will excel at numerous criteria related to energy efficiency and design. The elegant but expensive entry (shown above) from Technische Universität Darmstadt took first place that year. The angled slats in all those louvered folding doors are actually slim photovoltaic or PV panels. Occupants can adjust them for solar gain by day and privacy by night.
I didn’t realize it then, but as the New York Times explains, Darmstadt is the home of the Passiv Haus:
The concept of the passive house, pioneered in this city of 140,000 outside Frankfurt, approaches the challenge from a different angle. Using ultrathick insulation and complex doors and windows, the architect engineers a home encased in an airtight shell, so that barely any heat escapes and barely any cold seeps in. That means a passive house can be warmed not only by the sun, but also by the heat from appliances and even from occupants’ bodies.
And in Germany, passive houses cost only about 5 to 7 percent more to build than conventional houses.
Decades ago, attempts at creating sealed solar-heated homes failed, because of stagnant air and mold. But new passive houses use an ingenious central ventilation system. The warm air going out passes side by side with clean, cold air coming in, exchanging heat with 90 percent efficiency.
“The myth before was that to be warm you had to have heating. Our goal is to create a warm house without energy demand,” said Wolfgang Hasper, an engineer at the Passivhaus Institut in Darmstadt. “This is not about wearing thick pullovers, turning the thermostat down and putting up with drafts. It’s about being comfortable with less energy input, and we do this by recycling heating.”
More sub
My only reservation about the typical solar decathlon homes, and indeed most solar homes that I have seen, is that they are freestanding, hence suburban, structures. It would be interesting to address energy efficient design in an urban setting, where warming sunlight may be impeded by or shared between close neighbors.
Some friends of mine in Flagstaff are working on some of these issues for a client. The multifamily aspect adds some interesting challenges as well as advantages to PS design. The ratio of envelope to enclosed space is reduced which generally translates as decreased heat loss but also restricts solar gain to any single unit. Staggering the south and east walls as well as second story elevations of the units would seem to be a starting point. Here is a link to an abstract of some work done at Harvard on multifamily structure(s) passive solar design. I haven't read it, so I'd be interested to hear a report if you buy it.
December 29, 2008 3:43 AM | Reply | Permalink
This is way over my head. I thought ventilation was all important. Keep the air moving. How can you accomplish that in a vacuum?
You say that is taken care of.
This is really fascinating stuff.
December 29, 2008 9:52 AM | Reply | Permalink
They do ventilate. The trick is to prevent losing the energy you put into the interior air. The exchange is done between incoming air and exhaust air.
December 29, 2008 10:28 AM | Reply | Permalink
I have my doubts about relying so heavily on mechanical systems in one's home. If there should be a brownout in winter, one would be forced to choose between keeping in the heat and admitting fresh air.
December 29, 2008 11:53 AM | Reply | Permalink
The ventilation system can be passive, rather than active, even with the heat exchanger in place. However, the more effective the heat exchanger is, the lower the volume of passive exchange will become.
In general, though, if the power is out, so is the heat, in most modern buildings. Even if you have gas heat, forced-air furnaces require power for ignition and circulation. So this is not making things any worse.
December 29, 2008 3:54 PM | Reply | Permalink
Not a great sales pitch.
December 29, 2008 4:22 PM | Reply | Permalink
Another argument for batteries first.
December 30, 2008 12:04 PM | Reply | Permalink
Urban buildings are easier to make efficient, and most already are. (Few are aggressively so.) Chicago is pushing green roofs, for heat control in summer and for cleaner water runoff, which helps the water treatment system. But the city has also altered its deal with electricity suppliers, dropping their anti-competition requirement of outlawing rooftop solar or wind.
The most efficient living conditions in the country are in Manhattan, if we divide energy use by number of users. Suburbs are very wasteful so that is where much effort should be directed, as long as suburbs are being built. Whether they should be built is a different question, and few defend their increase.
December 29, 2008 10:34 AM | Reply | Permalink
This goes right to the American dream. By the fourth grade I found myself in the suburb. Just the space alone tells you that urban centers are going to use energy, space, and water much more efficiently.
Your reference to old anti-competitive legislation really intrigues me. But I think it has been clear from the beginning that there was a lot of graft with regard to energy grids and payoffs--that was Enron.
I also am intrigued by the fact that there are so many different ways to approach energy efficiency.
I like this short blog as well as comments.
December 29, 2008 11:48 AM | Reply | Permalink
The contract between Chicago and Commonwealth Edison used to be a flat fee, unmetered usage. City could use what it liked, ComEd had a large guaranteed income. Unfortunately it encouraged nonstop excessive street lighting. It has been changing over the years, with ComEd encouraging a shift to sodium-vapor lights as lower-demand, for example. But the incentives for the city to economize were few, and the state regulatory board was pretty much in bed with industry.
It's changing now, probably as the power line item becomes a larger piece of the city budget. If surpluses ever return, the city may pony up for its own power generation, to run CTA trains and other things. For that matter, the "L" trains should be very low-demand since they can return power to the rails on braking, friction is very low, and air drag trivial. Covering the outdoor rail lines with solar panel canopy would be enough power, I think, for them to be net zero demand.
December 30, 2008 11:58 AM | Reply | Permalink
An untapped advantage apartment buildings could use is to avoid large demand-surcharge costs by using a battery set. Electric power companies ask for the surcharge to offset having to supply surges for elevator use. Just enough battery to handle those peaks would smooth the usage curve and save enough to pay for the batteries fairly quickly. Would be nice for tenants to be able to escape in a power failure, too. That might reduce insurance costs.
December 30, 2008 12:02 PM | Reply | Permalink