Monday, November 2, 2009

Annualized Geo-Solar

Annualized Geo-Solar (AGS) is an approach to heating and cooling buildings which has not entered mainstream construction practice, yet holds promise for improving the energy performance of buildings in all climates. AGS is a method of balancing seasonal temperature differentials by capturing and storing summer heat in a thermal mass medium and re-radiating it back into the climate-controlled space as needed during the following season. AGS is an extension of the logic of passive solar design where the same process is employed on a diurnal cycle. Where passive solar designs are inherently limited by site requirements for adequate southern exposure, and more importantly, by harsh climates with protracted sunless periods, AGS is a more widely deployable technology.

Water is an ideal collection medium, though as in the diagram above, air also works for lower cost systems. Using low-energy solar pumps or thermo-siphoning, solar collectors are placed in full sun to heat water or air which is then transferred to the earth beneath the building surrounded by an insulation skirt. It is a simple matter to collect, store, and reradiate the required number of BTU’s of heat required to keep a well-insulated building comfortable throughout the winter. If these processes were industrialized, the low-tech flat plate solar thermal collectors, solar pumps and foam insulation required for a typical installation of this type of system would be comparable to a conventional heating system and would provide a lifetime of home heating and hot water.

Currently AGS technology is used primarily by those in the natural building movement who favour a low-technology approach to building and tend to prefer air as a collection medium, which is more affordable and less complex than water-based systems. The use of air as a collection medium often results in lower performance relative to water since air has less capacity to store and transfer thermal energy. Further, when the heat is to be reradiated into the building the following season, water provides a means of highly controlled distribution through in-floor radiant technologies where air presents greater challenges to effectively distribute.


AGS technology needs to be deployed with water-based collection, control, and distribution methods in order to be commercially viable in the industrialized world, though the simplicity and extremely low-cost of air-based collection methods are appropriate in the developing world where fewer resources are available. This approach to heating and cooling is widely deployable in the context of a subsistence urbanity whereby the costly infrastructures of natural gas and other types of fossil-fuel or wood-based heating systems are unavailable. With the use of low-energy pumps, AGS systems are appropriate in relatively high density situations in which the collectors are mounted on a flat rooftop of multi-storey buildings as a trellis-like assembly to provide shade for occupants. The aggregate effect of this practice would have an added benefit of reducing the urban heat island effect by sequestering heat. This approach is also viable in cooling buildings in a hot climate situation where thermosiphons or pumps run in reverse during cold nights or seasons.

AGS has the most potential as an autonomous system, though it could also be used in district heating installations where appropriate. These technologies have the potential to dramatically reduce or eliminate the use of fossil fuels and wood-burning in the operation of residential and light commercial buildings in cold climates.

Below is an example of a super-insulated natural building heated by AGS which I built as a site instructor with the Sustainable Building Design and Construction Class of 2006.

The following is excerpted from

“Warm air is collected from under the steel roof on the south side of the building during the warm months of the year. This air is blown through a long tube that travels 3 metres beneath the ground under the building before returning to the roof to be warmed again. The air warms the mass of the earth beneath the building, and this heat begins a slow rise upward through the soil. It will take approximately 6 months for the heat to finally be released into the building, so early spring’s stored heat becomes early winter’s heat inside the building. The system is turned on in early May and is turned off in late September or October. This system cost less than $500 to install, and has the potential to provide a significant amount of the building’s heat. It will take up to five years for the ground to fully “charge” with heat, so the success will only become evident over time. The thermometer display on the north east side of the building shows the heating tube and floor strata temperatures, so we can monitor its progress.


Is AGS a proven heating system?

No. There are only a few buildings in the world that use this kind of AGS heating. Reports from several of these show that after a few years they provide the majority of the heating requirements. The depth of the pipes under the ground, the amount of heat gathered under the roof and the strength of the fans in the pipes can all affect the outcome, as can soil type, ground water levels and many other factors.

Why use air instead of solar-heated liquid in the AGS system?

While water is a more efficient medium for storing and moving heat, the air-based system used here is remarkably simple. Solar water heating systems are more expensive and complex, requiring collectors, pumps, tubing and sensors. The air system uses two small fans hardwired directly to their own PV panels, and some inexpensive plastic piping. The system can’t overheat, doesn’t need maintenance and has only two, inexpensive moving parts."


Posted By Nathaniel Anderson


  1. So, have you installed the sysytem? If so, how is the system performing?

  2. This is an interesting concept. How do you find the information to design a system for the size of house and climate that you live in?