Geo-Air Systems
Geo-air systems rely on low-tech designs for a simple, affordable, easy-to maintain and cheap-to-operate geothermal heating and cooling. The principle of geo-air is that it relies entirely on air traveling through underground tubes to carry geothermal energy from one location to another. This system uses simple blowers and does not need heat exchangers or a geothermal heat pump. In fact, in cases where a heat pump is indicated, an ordinary household heat pump can be used, which is much less expensive than specialized geothermal types.
The simplicity of a geo-air system means lower construction costs, easier maintenance, and much greater longevity. The basic system is energy efficient and sustainable, with low operating costs. Even if a heat pump is necessary in very cold climates, it can still operate effectively since it will be working with air at an ambient temperature of 50 degrees F instead of sub-freezing.
In fact, a geo-air system with nothing more than air circulators is reported to be so efficient that it is effective even to -30°F without supplemental heat. Even better, the same system also cools the greenhouse during the summer. With such low technology requirements and a basic setup that’s entirely passive, geo-air greenhouses can be used in virtually any country, climate or economy.
Thermal Battery Systems
Note: Several systems that move heat energy using air and tubes are conflated, and you might hear any of them referred to as subterranean heating and cooling (SHCS), ground to air heat transfer system (GAHT), geo-air exchange, low-grade geothermal, thermal batteries, earth batteries, climate batteries, and so on.
In basic design, thermal batteries are very similar to geo-air systems in that they use buried tubing to move air and transfer heat. The goals may be slightly different, though. In fact, thermal battery systems may even be used for cooling: during the day when the greenhouse interior is being heated by the sun, thermal battery fans push heated air from high in the greenhouse down through underground tubing. This warm, moist air cools as it runs through the tubing, depositing heat by conduction into the surrounding soil, and through condensed water vapor with latent heat, through perforations in the tubing. This cooled, dryer air returns to the greenhouse space, cooling and drying the greenhouse, and regaining its capacity to absorb moisture and heat from the greenhouse again. It is a simple form of the heat pump cycle, that takes advantage of the latent heat energy stored in water vapor, and the phenomenon of condensation, by bringing the air temperature down to dew point through heat transfer to the cooler soil.
Geo-liquid exchange
It’s a basic physical property that dense mediums like liquids can absorb, store, and conduct more energy than air. This concept, is the basis of geo-liquid exchange systems, often called geo-thermal heat pumps. These systems are, in principle, the most energy efficient means to absorb, move, and transfer geothermal energy. In some cases, liquid exchange systems may use a combination of water and antifreeze in a closed loop that’s circulated in tubes running through soil, underground ponds, or directly into deep wells in order to pick up geothermal heat. The warmed antifreeze/water mixture then runs through a heat exchanger, sending warm air in the greenhouse before it’s sent underground to pick up more heat. This extended process makes geothermal heat pumps substantially more complex and expensive than your common residential heat pump.
Alternatively, the system may employ a simple open loop, where naturally heated water is brought into the greenhouse to shed its energy while a separate system recharges the pool or aquifer with cooled water. Some potential issues with this setup are ensuring the purity of the water and filtering out debris and any potential biological contamination. It’s important, too, to avoid damage to the pond, aquifer, or ecosystems from external contamination or rapid temperature changes.
While geo-liquid systems are highly efficient at heat transfer, in practical applications they are complex, require expensive equipment and regular costly maintenance. They also have very high initial costs, which makes geo-liquid systems out of reach for many homeowners and commercial startups in the US, not to mention global populations.
