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A year-round solar greenhouse: Part III. (The Solar Cowboy).

CHRIS LA FORGE GREAT NORTHERN SOLAR

When we returned from our research trip (see the March/April 2003 issue) we went out to the greenhouse and sure enough, even without the active solar heating system installed, the building was warmer than our passive solar house. A successful start to what might be the best way to heat any building.

When the final sketches for our building were being developed we had the help of our friend of many years, Michael Peyton. Michael is a partner in Northern Vision Construction Services and an old hand at helping folks through the versions and revisions of building design.

After several revisions Michael came up with the drawings we would work with.

Drawing 1 (above) shows the west view of the building with the massive center wall, the south facing windows set in at 60 degrees off horizontal, the upper south opening windows for ventilation, and other details.

Drawing 2 shows the south side including the extensive vent below the 60-degree window array.

One thing not shown in the drawings is the design of the mass of sand below the slab for storing the heat generated by the active solar thermal system. In Photo #1 you see the "sand box" that we constructed above our 22 sand lift (for getting drainage on our heavy clay). The 22 foam panel "sandbox" is where we laid out the thermal tubes used for transferring the heat from a solar thermal array into the 12 inches of sand above the tubes. The yellow foam board insulates the "sandbox" to maintain the heat storage as it is banked. In Photo #2 the sand is introduced and compacted and then the rebar is laid out and ready for the concrete.

All this work raised the building two feet off of grade and provided 17 inches (12 inches of sand and 5 inches of cement) of thermal mass to store heat for periods of low solar input. (In our neighborhood that time is called "November.") We've seen Novembers when the sun only came out on one day the entire month. To make the leap to the sunnier winter months we needed to make sure there was significant mass in the thermal storage. We asked Bob Ramlow of Artha Solar to help in the design and we came up with the layout.

Bob recommends as much as two feet of sand storage but we were concerned that it might not heat up fast enough so we went with 12 inches. That in addition to the five inches of concrete in the slab means that we can bank heat at the end of summer and have it stay. The exact choice of amount of mass was a blend of site considerations (How high were we willing to build the base of the building?) and thermal regulation (a cross between wanting to hold heat for long periods and yet not have it take too long for the storage to heat up). As with most issues in design, we talked long into the nights to come up with our answers. Through it all our friends in the industry were patient and helpful as we created our plan.

Once we got the sand compacted in the box, the rebar ready and the concrete poured, it was time for the passive solar storage--the wall! In Photo 3 you can see the start to the Flag method "slip form" wall construction. The forms were set on the concrete slab (which had to have a reinforced footer to support the 10.5-foot high rock wall) and coated with oil for easy removal. Two sets of forms were used to leave a gap where the arched doorway would be. The building of the wall was a major portion of the summer's labor and now in March we can tell it was worth it. Even without the high-mass radiant floor solar thermal system completed, the passive aspects of the design are keeping the building 30 to 40 degrees warmer than the outdoors. That, with some of the insulation not installed as well!

Next time we'll look at the raising of the wall, roof, and how we chose materials as we wrap up the story of the year-round solar heated greenhouse.

I did say I'd touch on the design considerations with reference to growing.

To be able to grow through the winter season the 60-degree windows bring in considerably more light in fall and spring. This angle also allowed for more effective ventilation when overheating might cause wilting. We wanted to be able to grow as long into the winter as possible, and then have the building hold heat so that we could maintain the plants as they became dormant. Helen and Scott Nearing indicated in their solar heated greenhouse book that many varieties of greens and other food crops would grow into the winter season and then slow in their growth yet remain healthy through the winter.

The angled glass with vertical glass above provided for maximum illumination short of putting glass horizontally overhead. Several of the growers in our neighborhood indicated that angled glass was the only way to go if we wanted adequate plant growth.

The details of the effectiveness of the design will take a year and more to understand what was best and what was not. Rest assured that as the data comes in we will be sure to share it with you. So far the work has been fruitful and it appears that we will be able to get our first set plants out of the greenhouse this spring even before it is completed.

The building will need a photovoltaic system in order to be a true "zero-net-energy" building so I'll detail that element along with the solar thermal system in articles to come.

Until next time, get the seeds started and get ready for another year on the homestead!
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Author:La Forge, Chris
Publication:Countryside & Small Stock Journal
Date:May 1, 2003
Words:984
Previous Article:Building and re-building. (Notes from the Northwoods).
Next Article:Build a low-cost solar water heater. (Alternative energy).


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