Construction - Passive Solar Heating System Completed

The solar heating system, after ten years of trial and error, has finally been completed.  It was originally designed to be entirely passive but it did not work as planned and a fan had to be added.  (Click on any photo for better viewing.)

The original design comprised an elaborate solar collector in a pit in front of the house that would harvest sun energy during the warm months and send it as heated air through nine conduits that are slanted slightly upwards and spread out under the house.  Heated air passing through the conduits would warm the thermal mass under and behind the house so that it would in turn warm the house during the cold months.  However, we soon learned that the legacy cold in the soil in which the conduits were buried pushed cold air downward through the conduits.  And the air in the collector was not hot enough or voluminous enough to reverse the flow.  The warm air would have to be pulled through the conduits from above.

Standing on end at the right, visually aligned with the bottom of the
PV panels in the background, is the short section of culvert before
 being partially buried in about the same location.

If air had to be pulled through the conduits, they could no longer emerge behind the house individually; they needed to be extended and converged at a "solar chimney" containing a fan.  Accordingly, a temporary chimney was cobbled together and pipes were run above ground to it.  A small furnace blower on a timer was installed in the chimney.  By the time the ugly temporary arrangement was replaced with the final iteration, it had worked well for two summers.

Since the 4" PVC conduits were to be entirely buried, they were shorten back to where they were horizontal and below grade then, with couplings, transitioned to 6" PVC pipes that ran underground to the new solar chimney.  On the way to the chimney, the 6" pipes were consecutively wyed together so that only one pipe entered the chimney from each side. The vertical pipe inside the chimney that received them was a piece of 12" corrugated culvert buried deep enough to receive the pipes through holes in its sides then protrude about 2 ft above grade.

The stick-built housing enclosing the culvert and holding the blower rested on top of the culvert as well as on legs supported by

concrete pads.  The opening through which the fan blew the air, sucked from the conduits, faced north and was fitted with a door that could installed during cool months to keep cold air from falling into the conduits and diluting the hard-won heat stored in the thermal mass.  Another opening, that was large enough to allow replacement of the fan was caulked shut but could be accessed in the future. 

Our PV array is the smallest the vendor would sell us but, as we estimated years ago, turns out to be about right for our needs.  So the demand placed on it by the "non-passive" solar chimney fan has not been consequential, considering that our gride sourced electricity during the entire year of 2024 amounted to only $105.

As long as the conduits were individual and accessible above grade, there remained the possibility of capping some of them during the warm months which might be advantageous if the thermal mass gets warmer year-over-year as seems tentatively to be the case.  If so, perhaps the simplest answer will be to reduce the inflow of air by capping some of the conduits leading out of the collector.

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OVERDUE SHOUTOUT

It doesn't take much scrolling through our blog to appreciate the number of men and women who have contributed to our house building project.  Shown at the right is the plaque hanging in our entry foyer that acknowledges the many volunteers and contractors who have been involved in this ten-year project.  (It can be enlarged for better viewing by clicking on it.)

And our plumber friend Bob Morgan, who came into our lives too late to be included on the plaque, took the lead for the project described here.