Every Growing Dome® Greenhouse comes standard with a geothermal climate control system. At Growing Spaces, we call it the Undersoil Ventilation System; previously known as the central air system, or undersoil heating & cooling system. There are many different names for these types of systems, such as Climate Battery, Earth Tubes, Subterranean Heating and Cooling System (SHCS), or Ground To Air Heat Transfer System (GAHT). All of which have slight design and installation differences. Some of these names and designs hold patents and/or trademarks. The system that comes with Growing Dome Greenhouses is very different in design. It is not as complex or powerful, and therefore, much easier install. All of these systems seek to achieve the same goal. Their purpose is to utilize the consistent temperature of the soil, tap into the thermal mass, and have the ability to store and release that thermal energy. The fan(s) used in these systems help circulate the air within the greenhouse as well — bonus!
In January 2021 we replaced the wooden fan box and 70 CFM fans in the raised beds with a reversible 125 CFM bilge fan that is located behind the water tank. This not only improves airflow in the undersoil ventilation system but saves on valuable raised bed space! It increases the efficiency and reliability of the undersoil climate control system, and also reduces the time and cost to install. It is also easier to reverse the direction of the fan in the winter to get more heat from the south side of your dome to the pond.
The main difference between our undersoil ventilation and a climate battery or GHAT system is that our system uses the soil in your raised beds as the thermal mass, and the other systems use the Earth below the greenhouse. Excavating the earth before your greenhouse build can increase cost, but can be useful to add additional heat in colder climates (zone 4b or below).
True geothermal heating systems actually use the heat from the Earth’s core to heat the greenhouse. Obviously, you would need access to this heat from a hot spring or a well. Luckily, here in Pagosa Springs, CO we have the deepest Hot Spring on the planet which provides heat from the ground to the town and three 42′ Growing Domes at the Geothermal Greenhouse Project. Feel free to call us if you want advice on these or other types of geothermal systems for your greenhouse.
The Undersoil Ventilation System
In order to utilize the natural thermal capacity of the soil beneath the greenhouse, perforated 4″ pipes are placed in the perimeter raised beds then buried when filling with soil. The end of the pipes come out of the soil in the south beds and are protected by a landscaping box that is provided with the kit. The end behind the above-ground pond either intakes or exhausts is behind the pond depending on the season. A PV solar panel mounted on the Growing Dome greenhouse powers the fan.
Since it is solar-powered, it will only run during the day when the sun is shining. For this reason, we recommend reversing the direction of the fan each season. In the winter, the fan should be pulling air from the south side of the dome to help heat the tank during the day. In the summer, the fan should be reversed such that the fan is pushing cool moist air from behind the tank, through the beds, and into the Growing Dome.
At 125 cubic feet per minute (CFM), this system helps warm the soil in the winter and cool it in the summer. Additionally, the fan moves and circulates air in the greenhouse in an open-loop system. With our greenhouse designs, year-round growing is a reality.
It is important to note that the Undersoil Ventilation system is installed inside your interior planting beds, and may vary based on your raised bed designs and the location of your door.