PASSIVE SOLAR ADAPTATIONS IN EXISTING HOUSES, PART 2

We left off with a minor passive solar project outlined, a 1000 square foot bungalow winterized and solarised in Columbus, Ohio. Calculations for a clear day in January suggested that about two/thirds of the heating load for the day would be provided  by passive solar. The additional  investment to achieve this result would be minimal. A contrary example, with the same footprint, but wrongly oriented glass of equal area, performed poorly in comparison.

We did make a few assumptions; firstly, the house has good solar exposure in winter. This is non-negotiable, clearly. The second assumption is that the house has a long wall facing south, i.e. the long axis of the house is more or less on an east-west line. This is much more negotiable. Even an orientation 30 degrees away from the ideal or a different plan shape is still workable.

We made  a third assumption of a ground floor slab-on-grade with 3 inches of under-slab foam insulation. This is unlikely to be the case. More often, the average house in a cool climate will have a basement with an uninsulated slab that gets almost no sun, and with a joist and strand-board and carpeted main floor over. The foundation walls  are masonry or concrete, but  probably insulated on the inside. All this mass in the basement is useless for heat storage.

The available thermal mass of the house will be much smaller, roughly 60 cubic feet of the gypsum core of the drywall on the ground floor being the only significant component with a heat capacity per cubic foot close to that of concrete, but somewhat insulated by the thick paper facing. We'll use this more typical bungalow with basement as our example as we proceed with our investigation.

We hinted in the first part of this article that an economical and elegant means could be found to achieve the effect of thermal mass without attempting to retrofit the house with an impractically bulky and massive thirty-six ton Trombe wall.

John Michael Greer, in his post Alternatives to Absurdity characterized the passive solar techniques of the 70's - including thermosiphon air panels, Trombe walls, and attached greenhouses, as baby steps towards learning to live comfortably on nature's diffuse energy flows. I'd like to suggest an order of magnitude improvement to the design problem of heat storage in a passive solar house, an idea of tremendous potential that was indeed researched, patented, but with the subsequent cheap oil and good times starting in the 80's, was never commercialized, and remains largely overlooked. A curious fact, that such an energy-saving invention was buried.

Passive Solar Adapations in Existing Houses, Part 1

In John Michael Greer's entertaining post on the Energy Bulletin of April 6, 2011, Alternatives to Absurdity, he noted that passive solar opportunities in existing construction are more limited than in new. He went on to inform his readers that passive solar requires that "a good part of the south or south-east face of your house receives direct sunlight during at least a significant fraction of each winter, spring, or autumn day."

Around winter solstice is the crucial period to check thoroughly, for if the south wall is in sunlight for the critical hours between 9 a.m. and 3 p.m. one can be assured of sufficient sun in spring and fall as well. Old Sol will not soon alter his course through the heavens, and deciduous trees will spring into leaf and later let their leaves fall just when it will benefit the passive solar householder the most.

Where John Michael Greer's missive may have been overly enthusiastic, it seems from this humble writer's viewpoint, was in a bit of advice given to homeowners in the latter half of the essay. That is, I wish to add a note of caution, lest an army of intrepid Do-It-Yourselfers begins casting new Trombe walls in living rooms across America for passive solar heat storage.

The Wonderful Machine by Charles Robert Beckett

It was coming on frost. Karl knew it with all his senses as he turned northward out of his lane and onto what was still called the Old Milford Road, though it was barely a cart trail now. He'd farmed all his sixty-eight years, and was as fit and fine a man as you might want, for his age. He'd been born here, at Headwater, in Prince Edward County, in 2043, just as the Long Troubles were drawing  to an end  in the Americas. Karl Hillier was the patriarch of an extended family of five couples, including himself and his wife Angelina, their married children, grandchildren, and his aged mother Sarah; four generations of Hilliers and twenty-three mouths to feed, in all.

The farm at Headwater provided well enough for them all, with good harvests for the last several years. By law, they would  have to keep at least a year's worth of food in storage, some as grain in the attic that he had built when he first married, some as various dried and preserved nuts, meats, fruits, berries, vegetables and legumes in Angelina's pantry off the kitchen. The Elders might order the distribution of stored food throughout the County, or its collection for shipment to some hard-hit region in a famine year, though that rarely happened anymore. 

 Headwater Farm also boasted an ancient but ample root and wine cellar, with the drying attic over, and most precious, the original attached greenhouse for fresh herbs and a few  greens in winter. There was a good barn and stable to feed and shelter the draft horses, oxen, and the lambing sheep through the coldest months, a solid hen-house, a pigsty and a drive shed. He and Angelina had been happy here, raising their family and building up the farm; it would be fifty years together next Midsummer's Day.