Thursday, July 31, 2014

Timeline - Annualized GeoSolar (Cont'd)

This is the second in a series of posts on Annualized GeoSolar, the passive system for heating and air conditioning that we will use for our energy neutral house.  To check out the first post, go to Annualized GeoSolar.

I became acquainted with AGS 7 years ago when stumbling upon an online paper by Don Stephens*.

The Father of AGS
Before discussing AGS, I would be remiss if I failed to give credit to John Hiat who, in my opinion, is the father of AGS-like concepts.  He self-published his spiral bound "Passive Annual Heat Storage -- Improving the Design of Earth Shelters" in '83. Stephens subsequently improved Hiat's PAHS and called it AGS but his detailing of the whole system is much sketchier than Hiat's. In fact, I think anyone contemplating building or buying an earth shelter would be remiss in not reading two books -- Hiat's book and that of Carmondy and Sterling, "Earth Sheltered Housing Design", (Hiat gives much credit to the latter in his book). (Both books are out of print but, as of this writing, were available on EBay.)

Hiat's Influence
Until Hiat and Carmondy/Sterling came along, I am pretty sure passive solar heating was universally synonymous with solar energy from the winter sun (irrespective of earth sheltering). Stephens refined their work and named it AGS to differentiate its year-long cycle from the spasmodic daily, or even hourly, cycle of conventional passive solar heating that depends on the whims of winter sunshine.  
Hiat's iteration of the insulation/watershed umbrella

How do PAHS and AGS Work?
Both writers advocated using concrete for at least the floor of the house, installing lots of south-facing glass and earth sheltering the roof as well as most of the west, north and east walls. Both advocated keeping the soil around and under the house dry and insulated by extending waterproofing and insulation horizontally from the house below 
grade and outward twenty feet in all directions, thereby maximizing the thermal mass available to absorb, hold and dispense heat.  I have chosen to adopt Hiat's terminology for the horizontal insulation and waterproofing --  "Insulation-watershed umbrella".
Solar collector (blue), conduit (red), solar chimney (green)

Stephens' important upgrade was to use a homemade solar collector downhill from the house with conduits, tilted slightly upward, running under the house and exiting to daylight behind the house in a solar chimney.  The collector is designed to maximize solar gain from the summer sun and the conduits are designed to carry heat passively to the soil under the house before exiting via the chimney.

Managing the System
When cool weather approaches, the chimney is closed so that cold air does not drop into the conduits.  The heated thermal mass (concrete floor and walls plus the soil beneath the floor, under the umbrella and behind the earth contact walls) then maintains an even temperature within the house during the winter, independent of passive solar gain through the windows. Spring arrives, the chimney is opened and the collector begins to recharge the system before enough heat has escaped around the edges of the horizontal insulation to lower the temperature in the house more than a few degrees, if any.

Year-round Comfort
The year-round temperature can be slowly (over a couple of years) adjusted to, and then maintained at, any desired temperature, say 74 degrees, plus or minus two degrees. In addition to providing heat during cold weather, the massive heat sink plays the role of air conditioning by absorbing any summer heat penetrating the envelope of the house and storing it for the next winter.

CLICK HERE to access the last post on AGS
* Although Stephens' paper,, is no longer available, it can be accessed indirectly at Stephens' definitive paper

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