Annualized geo solar
Annualized geo-solar (AGS) enables passive solar heating in even cold, foggy north temperate areas. It uses the ground under or around a building as thermal mass to heat and cool the building. After a designed, conductive thermal lag of 6 months the heat is returned to, or removed from, the inhabited spaces of the building. In hot climates, exposing the collector to the frigid night sky in winter can cool the building in summer.
The six-month thermal lag is provided by about three meters (ten feet) of dirt. A six-meter-wide (20 ft) buried skirt of insulation around the building keeps rain and snow melt out of the dirt, which is usually under the building. The dirt does radiant heating and cooling through the floor or walls. A thermal siphon moves the heat between the dirt and the solar collector. The solar collector may be a sheet-metal compartment in the roof, or a wide flat box on the side of a building or hill. The siphons may be made from plastic pipe and carry air. Using air prevents water leaks and water-caused corrosion. Plastic pipe doesn't corrode in damp earth, as metal ducts can.
AGS heating systems typically consist of:
- A very well-insulated, energy efficient, eco-friendly living space;
- Heat captured in the summer months from a sun-warmed sub-roof or attic space, a sunspace or greenhouse, a ground-based, flat-plate, thermosyphon collector, or other solar-heat collection device;
- Heat transported from the collection source into (typically) the earth mass under the living space (for storage), this mass surrounded by a sub-surface perimeter "cape" or "umbrella" providing both insulation from easy heat-loss back up to the outdoors air and a barrier against moisture migration through that heat-storage mass;
- A high-density floor whose thermal properties are designed to radiate heat back into the living space, but only after the proper sub-floor-insulation-regulated time-lag;
- A control-scheme or system which activates (often PV-powered) fans and dampers, when the warm-season air is sensed to be hotter in the collection area(s) than in the storage mass, or allows the heat to be moved into the storage-zone by passive convection (often using a solar chimney and thermally activated dampers.)
Usually it requires several years for the storage earth-mass to fully preheat from the local at-depth soil temperature (which varies widely by region and site-orientation) to an optimum Fall level at which it can provide up to 100% of the heating requirements of the living space through the winter. This technology continues to evolve, with a range of variations (including active-return devices) being explored. The listserve where this innovation is most often discussed is "Organic Architecture" at Yahoo.
This system is almost exclusively deployed in northern Europe. One system has been built at Drake Landing in North America. A more recent system is a Do-it-yourself energy-neutral home in progress in Collinsville, IL that will rely solely on Annualized Solar for conditioning.