True geothermal greenhouse 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 providing 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 to tour these geothermal greenhouses, our six Growing Domes on-site in Pagosa Springs, or simply if you want advice on these types of geothermal systems for your greenhouse.
But what if you don’t have access to geothermal heat from the Earth’s core?
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 to 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 GAHT system is that our system uses the soil in your raised beds as the thermal mass, while the other systems use the Earth below the greenhouse as a heat exchanger. Excavating the earth before your greenhouse build will increase cost, but can be useful to add additional heat in colder climates (zone 4b or below). We recently published an article on a customer who did install a Climate Battery under their greenhouse in order to grow tropical plants all year long in Colorado!
When installing an underground heat exchanger, it is highly recommended to install Insulated Concrete Forms (ICF) as your greenhouse foundation. These can also be extended above-grade and replace the wooden stem wall provided with the greenhouse kit. This is one of three foundation options offered by Growing Spaces, and we can provide engineered drawings and recommendations for ICF Suppliers.
The Undersoil Ventilation System
In order to utilize the natural thermal capacity of the soil in your greenhouse, perforated 4″ underground pipes are placed in the perimeter raised beds and then buried when filling the beds 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 other end is behind the above-ground pond, and either intakes or exhausts depending on the season. A PV solar panel mounted on the Growing Dome greenhouse generates power for 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 soil in the beds, and into the Growing Dome.
At 125 cubic feet per minute (CFM) air flow, this system helps warm the soil temperature 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.
Please contact Growing Spaces directly for more information on the different options for climate control systems in your Growing Dome greenhouse. We also partner with Eco-Systems Design on Climate Battery designs for the Growing Dome greenhouse.