Passive+Annual+Heat+Storage

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2.1 An ISOLATED-GAIN SOLAR HEAT-SOURCE.

While such a source would typically be an air-based solar device (such as the sunspaces, greenhouses, thermosyphon flat-plate collectors or sub-metal-roof-surface plenum spaces mentioned above), the storage could, instead, also be charged by any of a range of other choices. These might include an outdoor, summer-fired wood furnace or pottery kiln, water-filled extraction tubes running through a "hot" compost pile, directly wind-powered electric resistance coils, etc. It's also possible to divert unwanted warm summer attic or near-ceiling air into the poly dispersal tubes, thus storing this excess warmth for seasons when it will be better appreciated, while also reducing or avoiding entirely, the need for costly air conditioning. This heat source is connected to the...

2.2 INSULATED TRANSFER-DUCT SEGMENTS and UNSULATED HEAT-DEPOSIT TUBE

SEGMENTS These carry that heated medium (air or whatever), with minimum losses, down into an adequate mass of dry earth, for storage and time-lagged transmission, before reaching the underside of...

2.3 The CONDUCTIVE FLOOR MATERIAL

(In the Heat-return Zones), this facilitates upward heat transfer and radiates and convects warmth out into the living spaces above, to replace losses occurring through windows and other perimeter surfaces.

2.4 A planned method of assuring the 6-MONTH CONTROLLED-LAG HEAT RETURN

This is accomplished by making the heat travel a predetermined number of feet (depending on soil type) in the dry earth (either vertically, between deposit level and the slab above, or horizontally, between a deposit site directly beneath the insulated center part of the floor and the nearest un-insulated perimeter slab areas, where it can then conduct upward un-impaired ...(see again the flywheel options diagram above) ...This latter approach is usually the easiest answer (unless, for other design reasons, deep compacted fill is being placed beneath the floor, anyway) - no deep ditches / less "diggable" soil depth required.

2.5 Some OUTLET OPTION at the exhaust end of the deposit tube

A solar chimney (for a totally passive flow, where other factors make that possible) or an adjustable lowspeed extraction fan (can be PV-powered), and a dampered exhaust outlet, or return of the medium to the isolated heat source for re-warming.

2.6 A perimeter, sub-grade MOISTURE-DIVERSION MEMBRANE/INSULATION CAPE

This extends from the structure's walls to an outer edge a minimum of 20 feet [6.5 meters] away from the nearest deposit tubes/ducts, to prevent "short-cutting" back to the outside ground surface, instead of coming up, as wanted, through the floor, and to direct roof and surface rain/snow-melt run-off away, preventing it from trickling down through the heat-storage and buffer-zone soil and robbing warmth stored there. (I typically call for a layer of salvaged, used carpet atop that membrane, to protect it during top-soil placement and planting - this is both a great positive re-use and a carbon sequestration tactic for a major waste-stream item. The insulation itself can be conventional foamboard or, preferably, one of a range of salvaged insulating materials.).

2.7 SIMPLE CONTROL SYSTEMS

These regulate when heat-flow to the deposit zone is active and when all exhaust convection is to be blocked (to prevent the unwanted venting of precious, previously earth-stored heat.)

2.8 A Few Simple THERMAL SENSORS

These can be as simple as the inexpensive auto-supply-store digital thermometers with remote sensors on thin wires, to be placed down 1" [2.5 cm] pipes...allowing annual monitoring of storage-zone temperatures, to chart its year to year warming, and eventually, to help determine whether it may be necessary to restrict the amount of summer heat input, just to prevent possible winter overheating. (Some clients also install a few moisture-sensor stations in various places in the structure and the earth below, to check with a low-cost wood moisture-meter from time to time, for informational purposes.)

All this sounds far more complex than it really is, once one develops a sense of how it all comes together.

And the cost of adding such a system can be so small, when compared with the savings it returns over time...Just an enjoyable sunspace or simple collector (perhaps of salvaged materials), some corrugated polyethylene pipe as air delivery tubes (avoid toxic PVC), a simple solar chimney (perhaps also an opportunity for an interesting vertical design element?) or small PV fan to provide/assist flow. And in most cases, cost of the perimeter insulation cape is more than off-set by savings it facilitates in using much shallower footings, since frost then never reaches them.

[] This unique method for maintaining a deep-earth constant temperature of about 70o (21o C) is based on several principles of physics:
 * 1) Heat flows by conduction from warm places to cool places, and will ONLY return when the original source cools to a temperature which is below the storage temperature.
 * 2) Far more solar heat is available in the summertime than in the wintertime.
 * 3) Earth is an ideal thermal mass for storing heat over time periods well in excess of 6 months.
 * 4) The constant temperature 20 feet (6 m) into the earth is a reflection of the average annual air temperature.
 * 5) It takes six months to conduct heat 20 feet (6 m) through the earth.