Yes, More Solar

Not to belabor solar energy ... but I do want to discuss passive solar, and yours is the only question I could unearth with any reference to it. Which do you think Dearest Readers would prefer: that I write a fake passive-solar question, or that I use your actual question but talk only about passive solar, hence not really answering it? Maybe I'll fake a question for the next column and you all can decide which feels better. Or maybe my editor will decide.

I have written a little about masonry stoves previously, and I do intend to write about radiant floor heat in the future. Feel free to load me up with basic questions about radiant floor heat. To evaluate the heating systems that you mention, we must take the design of your home into account. As we all no doubt know by now, sealing the envelope of your home and reducing your heating and cooling loads is the No. 1 move in home conditioning efficiency.

My guess, as a segue, is that for reliable heat in a typical home, passive solar will be the worst of the three options you mention, because the home won't be designed to maximize the sun's benefits. I refer, of course, to the benefits of light and heat. The sun's light can replace interior electrical lighting, but only if windows and inside walls and furniture are correctly designed and placed. The sun can heat the house, but it takes careful planning to have the amount of heat you want from the sun, no more, no less.

Classic full-bore passive solar has five elements: the aperture through which sun enters the home; the thermal mass in which the sun's heat is stored; the absorber, which is the tempting surface of the thermal mass; the distribution system via which heat travels to all parts of the home in a timely and desirable manner; and the control to stop sun when its heat is unwanted.

Our homes have all these things, but usually in the wrong arrangement. Often that is what makes them so dang cold, or so dang hot in the summer. For instance, you might have plenty of apertures -- windows -- but on the west side instead of the south. Or you might have an absorber -- wood floor -- over a crawl space, instead of over a thick layer of thermal mass in the form of masonry, or water tanks. These absorb and store the solar heat and release it as the air cools. In well-designed passive-solar homes, the delivery systems for heat will be convection, conduction, and radiation, not electric fans or other mechanical gadgets. Controls are architectural features, or furnishings, that block the direct hot sun. A roof overhang is an example.

It is possible to retrofit or remodel a regular house to include passive-solar elements. Controls are actually some of the simplest to implement, and these are useful for avoiding heat. Roof overhangs that cut off the high angles of the summer sun can be replicated in awnings, shutters, shades, and landscaping. Changing out windows is another way to take advantage of passive-solar design. Modern windows can be tailor-made to enhance passive-solar gain, or block it. There are coatings that let in light but resist heat, or let in heat and light but don't allow heat back out at night. If you are doing a large remodel, adding an addition, or rebuilding part of the house, it's possible to bring passive solar into the architectural plans. A sunroom is one way to do this.

How, how, shall we learn more about this scintillating topic? Well I love the EERE, a well-flogged horse in this space; there is also a nice article on remodeling with passive solar at Home Energy Magazine, and information at the Consumer Energy Center. There are also quite a few books out there on passive solar that I haven't yet read, but they would be the next step in a serious consideration of any project involving the concepts.

Sorry I only began to answer your question.

Passively,
Umbra