EROEI of a Phase Change Material Passive Solar System

In an earlier article, published in two parts, Passive Solar Adaptations in Existing Houses,  we examined a hypothetical modest bungalow with passive solar potential. We assumed it was located at the 40th parallel, in Columbus, Ohio, one of the ten best cities in the US, I understand. By the time we hit our stride in the second part of the article, we had assumed  the house had a typical basement, and pressed on towards making it virtually self-heating in winter with a passive solar strategy.

We saw in Chart 5 of the article, that under average January conditions of occupancy, temperature, wind and amount of sun,  that the house would actually have a slight net heat gain over the twenty four hour period. Of course our renovation specifications were beyond typical building code standards, which represent only the legal minimum in construction quality.

Our passive solar strategy included:

·         modest window areas on north, east, and west walls, with low-emissivity sealed double glazing

·         extensive windows on the south wall, with heat gain low-emissivity sealed double glazing

·         stringent air-tightness, with energy-recovery ventilation

·         insulation standards 50% or more above building code

·         manually controlled insulating night blinds in lieu of conventional window treatments

·         innovative phase change material heat storage and retrieval system

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. 

Close to the Final Leg of the Roofline

Here in these photos you're able to see the scaffolding positioned, in this case, at the north wall so that each corner in its turn could receive the careful interior and exterior carpentry work required. On the last day the south side scaffolding travelled from west to east while the castellations were delicately figured along the roofline. The left photo is the final day's saunter back to the mini-house to prepare for the trip back to Oxford Mills and the end of this part of the work. The next leg of the journey for Andre and Rock would be the ferry crossing and the Loyalist highway to Kingston and Highway 15.

Perhaps we'll see the crew in the next months or early in the new year as we prepare to add windows, doors, and partition framing.

Truss Tales

Living with the construction crew on a day-to-day basis was close-up and personal in the mini-house (i.e. a cozy one bedroom home with a futon and some floor space). I think that now it's time that you get acquainted with them too.

To the left is Bob the Architect standing in his studio roof stepping down from the ladder and scaffolding to the North East corner of the main structure. He is happiest when he's on the job, everyone is at work, and coffee is ready soon.

Next is Rock from Oxford Mills, a carpenter and general contractor. Rock grew up in this area on a traditional mixed farm, is quiet, gentlemanly and equipped with a dry wit as well as his own foam cot for this rough camping operation, although the rolling up operation is a tricky job.

Alongside Rock is Andre also from this area and a carpenter who is widely skilled in the trade taking on exterior carpentry jobs from roof trusses to basement rough-ins and interior kitchen and bathroom renos. He is also a trained luthier (one who builds stringed musical instruments) and is always on the lookout for a fine piece of wood for the next instrument. He is known to observe the mini-house cooking very carefully to suggest the important ingredient of garlic to be used in almost everything.

Last is Mile who took on many tasks while carpenters did their skilled trade. He is a young Macedonian Canadian whose skills as a visual artist in the County are widely known. He is also part of Small Pond Arts where the creative team works in an interdisciplinary way to create events and festivals. These 'community-based art' projects inspire local artists and participants alike. He pitched in to skilfully make a special brew of coffee that was much favoured on the job site.

The team carefully skirted around each corner of the main section of the netzero home to form the elaborate corners that you see taking shape in this view.

Finally the south roof castellations were built on the last day, their indentations designed to accommodate the moveable solar panels that will be placed there later.

On their final walk home to the mini-house, the crew was very pleased with their efforts having closed in the structure so making it secure for the winter months that lie before us.

Truss Positioning is Delicate; the Results Dramatic!

Once the carpenters had had their Thanksgiving weekend, their turkey well tucked into their tummies, they returned to the construction site to make good on their promise to finish the roof 'before the weather runs out', as the eastern Ontario expression goes. They began with the double trusses of the studio roof positioning the main girder exactly as needed across from north to south. Once the main girder was in place, the diagonal girders were positioned into each of the north and south corners. Finally the large hangers were tacked in place.

The architect wanted to avoid the using oriented strandboard or chipboard but ordered tongue and groove exterior plywood. Once the girders and trusses were aligned and positioned according to the detailed shop drawings, this plywood was screwed into place. With the work requiring the bringing up of plywood sheets, winds became remarkably high entering into gusts of 50 and 60 kmph. Sheets had to be tipped down to prevent their flying and taking flight into the winds.

As I have come to understand, every succeeding trade tries to compensate for the previous crew's small errors and this construction site is not impervious to these errors. The carpenter crew quickly noted that the mason's wall on the northeast corner has a slight discrepancy and so the corner of the roof also echoed this and so on and so on... The attractive architectural facer conceals what ills have gone before.

When the trusses, girders and sheets of plywood were put in place and the last nail driven into 2X4's, the resulting roof structure had drama and elegance that surprised both the architect and his wife. In his quiet way, he said that it was his best work ever and I think you'll agree.