David Wright: Passive Solar Design
(Page 7 of 16)
September/October 1977
By Travis Brock
PLOWBOY: Yeah. You've told us how you got from active liquid systems to active air systems. But how did you get from there to passive systems? And what's your definition of a passive system anyway?
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WRIGHT: I think that the best definition I've heard of passive heating or cooling, humidifying or dehumidifying, or whatever . . . is that it's a way of conditioning a space without using commercial energy.
PLOWBOY: Without using commercial energy . . . such as electricity.
WRIGHT: Yes. In our modern industrialized society, commercial energy increasingly seems to come in the form of electricity. But it also comes in other forms: natural gas, oil, coal, propane, butane, and so on. So what we're talking about is designing a home or a workshop or an office or any other space that people will inhabit . . . and designing it in such a way that we really won't need any kind of commercial energy to keep it comfortable. We won't even need a little tiny bit of electricity to run a pump or a fan to circulate water or air through a collector someplace.
We're talking about designing a space so that no matter what goes on outside-no matter how hot or how cold, how wet or how dry the microclimate surrounding that space might getthe space inside will be a comfortable place to live. And it'll be comfortable just because of the way we've designed it. We won't have to pump in any electricity or gas or coal from 1,500 miles away to keep it that way.
A convection-type solar water heater is a nice, simple example of what I'm talking about. Such a unit consists of only two main components-a collector and a storage tank-and enough plumbing to connect them. Actually, it's just slightly more complicated than this since, if we didn't have some way to protect the water in the collector on really cold nights, it'd freeze and tear something up. But we can take care of that easily enough by making our insulated, indoor storage tank a tankwithin-atank . . . and then circulating only a water/antifreeze solution outdoors through the collector and then inside through the heat-exchange part of our storage tank.
OK. Since we all know that hot water rises and cold water sinks, it's obvious that we'd be foolish if we set our collector up so that it was higher than our exchanger tank. If we did that, the first water/antifreeze that got up in the collector when we filled the system would start to warm up . . . and the more it warmed, the more it'd want to stay right up there in the top of the collector.
And the only way we'd be able to push that hot water and antifreeze down to our heat exchanger tank would be by adding a pump and bringing in some outside energy-probably electricity-to run the pump. And then we could shove that hot fluid down to the storage tank, but it still wouldn't want to stay there. So we'd just have to keep pumping it back down as fast as it tried to rise or we'd have to put some one-way valves in the system or something and we'd have to keep pumping in outside energy to make this all work and we'd wind up with a very active and probably very inefficient water heating system on our hands.
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