Ever the iconoclast, or at least ever the wannabe, I spent a good number of my teen years insisting on an all-black wardrobe, and to this day I still have my happy black days. Leaving for school in September, Mom would always ask “Aren’t you hot?”
“Nah…” (yes, but it was about looking good. Sweat, what sweat?)
So everyone knows a black outfit on a hot day is very different than a white one, even when they’re otherwise identical. Black absorbs heat and white reflects it.
But just how useful might this principle prove in ecological design? What opportunities does it provide? Could we generate flow in still ponds with patterns of black and white stone? Create temperate and tropical microclimates right next to each other? How about artificial winds where the air gets purified as it flows? Could we reduce the need for powered heating and cooling with color? If so, painting the house isn’t just about pretty; it’s functional… and more profoundly beautiful.
So to grow as a designer and see what’s possible, I pulled together an experiment. It isn’t rocket science, and I know I’m not the first to do it, but it was great to engage.
With one of my wooden octahedron prototypes, about 3 feet to a side already painted black for the LooptWorks show, I painted the other one white. On each I put a triangular “table top” made of half-inch ply, one painted black, the other white. Then I lined them up about two feet apart along the sun-arc so that both got full sun all day and so that neither sat on a hotter or colder spot than the other.
The two octahedrons, one white, one black, side by side in the roof garden
With a laser temperature gun, I took the temperature at the center and corner of each table top, and for comparison, took the temperature of the tar-panel rooftop itself. I should also mention that I did this experiment on a hot LA August day, with not a cloud in the sky after the initial coastal burnoff by probably 10 am.
I found several relationships. When the sun is directly overhead, there was as much as 65 degrees F difference between the tabletops. The black might close in on 150 degrees F while the white hovered around 80 or 90. The difference fell quickly once the sun dropped to the horizon, and disappeared entirely once it was gone, so with sunlight out of the equation, factors other than color determine temperature.
Results from the temperature experiment, showing big differences between the black and white octahedrons
The temperature of the black octahedron swung wildly in daylight with even a slight breeze, more in the corner than the center. While I scanned with the temp gun for 20 seconds, the temperature at the corner might vary 10 degrees with a breeze. The thin plywood, with little thermal mass, would dissipate and regain its heat quickly. The white also fluctuated but not nearly so wildly. And the white sometimes even hung out in the 60 degree range while the hot sun roiled above, setting the roof ablaze to the tune of 120-140 degrees F. The temperature difference between the black center and black corner also varied as much as 20 degrees F while the sun was high up, showing again how the slight thermal mass and poor heat retention of the plywood gives it up to the air quickly.
So can we we generate flow in still ponds with patterns of black and white stone? Create temperate and tropical microclimates right next to each other? Artificial winds where the air gets purified as it flows? Reduce the need for powered heating and cooling with color? Yes, but exactly how and how much is a matter of more experimentation, as well as learning from people who have done these sorts of things, in some cases thousands of years ago, and in some cases learning from the most recent science available. A half-cup innovation plus a half-cup of remembering.
Thinking about the 2012 festival circuit, experimental structures in the “developing world” and some planned DIY offerings, this new awareness is definitely clarifying and helping to define some Vertecology build proposals already in the works.
Some design opportunities now apparent: Using a material other than wood will effect the temperature differences. Using steel or some kinds stone of could produce differences in the hundreds of degrees, maybe enough to turn electrical turbines or “magically” pull water out of “thin air,” though steel heat would probably dissipate a lot faster than stone heat.
Greater thermal mass would also take much longer to heat but also to cool, making it possible to radiate warmth well into the night and keep a house cool well into the day. And materials can be played against one another – low retention, low conductivity wood painted white, vs high retention and moderately conductive stone, vs highly conductive and low retention steel, to create truly designer passive solar effects.
Taking this into consideration, here’s one application of passive solar in a “permaculture structure” with multiple functions in the diagram below. This is based on solar updraft tower technology, and this specific set of diagrams takes the fuel-free energy-generation Botswana Solar Updraft test facility, which ran in 2007, as the starting point. (Their experiment documentation here).
Solar Updraft tower diagram, inspired by the Botswana Solar Updraft Test Facility, a fuel-less passive energy genesis system with more potential ecological benefits
While their small test tower would probably not generate much power, with the right combination and density of materials, its performance might improve dramatically without an increase in size. This at the very least would make a great project for the 2012 festival circuit, and it could become a model for community-scale free energy generation, desert-greening and even seed spreading and vertical habitat building… all at once. (I actually have less interest in really huge industrial versions of this structure 800 meters tall, which require industrial-scale funding, a corporate building approach, and which could have adverse effects on the earth’s atmosphere – think jets of our precious air superheated and streaming into space)
On a more immediate note I also now know why the Sugar Shack roof garden is frying, and we can do something about it. The first of the new tire planters has already been painted white, as of about 4 pm today.