My Mother's House Part VI

Enlarge Image Image Gallery [1] The skeleton of the batch heater, ready for reflectors. [2] The two center pieces of insulation must be beveled to fit snuggly at the cusp. [3] All insulation should be carefully taped to prevent air leaks. [4] The tank rests on supports cut into the three 3/4"" plywood ribs and stand formed from ""two-by"" lumber. [5] The completed collector resides behind the greenhouse's glazing. [6] Our smaller solar chimney. [7] The central sun-powered ventilator exhausts air from the roof peak.

If you've been seeking plans for the simplest type of solar water heater around, look no further.

Since our last visit to My MOTHER's House—when we described the building's hybrid solar heating system—the Eco-Village crew has been working on detailing our earth-sheltered dwelling. And among the numerous finishing jobs they've tackled were two energy-related projects that we'd like to describe in this issue's installment: our passive solar domestic water heater . . . and a pair of solar chimneys, which boost airflow through the home's interior on sultry summer days.

TANKS FOR THE MEMORIES

Of the many different systems used to heat water with the sun, only one kind of collector can claim a performance history of more than a century. The basic tank-in-a-box water-warmers first appeared in the 1870's, with the introduction of the Climax SolarWater Heater, and have enjoyed a varying amount of popularity since that time. Such devices go by a number of names—batch heater, breadbox, and integral passive solar water heater are a few of the popular terms—and there actually are some variations in their designs as well. However, these collectors all have one thing in common: real down-to-earth simplicity!

A typically configured batch heater consists of little more than a black-painted tank in a glazed, insulated box. The internal vessel serves as both absorber and storage container (thereby eliminating any need for the tubes, fins, and other paraphernalia common to flat-plate collectors), and water is moved through the system by either gravity or line pressure. In fact, one of the most popular ways to use a breadbox (this name derives from its resemblance—when fitted with an insulated cover—to that once common kitchen item) is to plumb the collector in right before the conventional water heater in order to preheat the incoming cold liquid.

Today, most batch heaters feature reflective surfaces—on the inside of the box, surrounding the water container—which bounce sunlight back onto the tank for maximum efficiency. Of course, there are many ways to go about building such reflectors, but most of them involve the use of some sort of curved metal surface.

BRINGING IT ALL BACK HOME

When we sat down to sketch the configuration of our to-be-built collector, we found ourselves caught in a bind between textbook calculations and the hard realities of available materials. As we worked, we tried to keep to the accepted guideline of providing 1.5 to 2 gallons of water capacity per square foot of collector, but—as is often the case when theory meets practice—a couple of problems got in the way.