The primary purpose of a greenhouse is to keep an environment conducive to sprouting, growing and fruiting plants, separate from local conditions. Usually, that means keeping a greenhouse warm in cool climates or extending the growing season into fall or winter, and sometimes it means growing food crops all year round.
Light and warmth are typically the elements that require the most attention. To provide light, greenhouses are enclosed in transparent or translucent structures that protect plants from extreme temperatures, predation, wind, and other hazards. These panes or panels aren’t necessarily great insulators, though, and the colder your climate is (due to latitude or altitude), the more attention you’ll need to pay to maintaining an ideal temperature for your crops.
By their nature, greenhouses benefit from passive solar heating - incoming rays from the sun pass through the clear walls and their heat is trapped in the confined air. However, an unheated greenhouse, even with double layers of thick film panels, will only stay a few degrees above the ambient temperature in the winter. In addition, the sun shines considerably less than 12 hours per day in higher latitudes and even when all maximum available heat is trapped from solar radiation during the day, the temperature will still drop overnight.
Built above ground, highly insulated greenhouses require significant energy to heat when compared to even the simplest of geothermal options. For example, a greenhouse sunk 4’ below ground with an underground soil temperature of 50° only needs an additional 30° to reach an ambient temperature of 80°, whereas in a surface structure, a ground temperature of 10° requires 70° worth of heat to reach the same internal temperature.
Many enthusiasts will turn to supplemental heating at this point - perhaps through a kerosene heater, a wood stove, an electric space heater, or some other device. Unfortunately, providing heat for a greenhouse is an expensive proposition, especially if you’re working on a commercial level where profit margins tend to be on the low side. Then there are the inherent risks that accompany these solutions.
Fossil fuels, like propane, natural gas, gasoline, and diesel are unsustainable and emit high levels of CO2 to the environment. These fuels tend to be slightly more affordable than electricity, which isn’t available in all agricultural areas either. If a fuel isn’t available or sold in your area, you can’t rely on it for stable heating. Combustion heaters running on gas or liquid fuel generate noxious fumes that can damage plant growth or risk the health of your greenhouse employees. Passive solar heating may sound great since it’s so affordable and sustainable, but it only works in certain climates and may fail during a winter that is colder than expected. Finally, the costs of all these heating methods tend to fluctuate from year to year. Even one or two years of extreme weather could wreak havoc on your operating budget. However, once you’ve made the initial investment on a geothermal system, the cost to operate it will vary only slightly, and even then, only if your system uses electricity.
What are the Advantages of Geothermal Greenhouses?
- Passive geothermal heating has no operating costs other than periodic maintenance needs.
- Generates no CO2 or other pollution during operation and minimizes the need for electricity.
- It’s possible to build geothermal systems in remote areas where there’s no electricity service or delivery service for fuel.
- Maintenance and daily operations can be focused on your crops rather than expensive, power-hungry equipment.
- Since geothermal energy is not affected by weather, your heat source can be relied on even during seasonal storms.
What are the Potential Disadvantages of Geothermal Greenhouses?
- Establishing a geothermal system can be expensive. Even for passive systems, just excavation and drilling can represent a large up-front expense.
- Dry sandy and loose soils aren’t optimal for geothermal wells and boreholes, since that type of soil may not be structurally stable for deep vertical drilling. Even for earth tubes and similar systems, loose, dry ground is less efficient at transferring heat.
- If your system does use electricity for fans, pumps and other equipment, you are at risk for power outages during winter storms. Fortunately, this kind of equipment generally requires very little power which can probably be provided using batteries or a small generator.
How Can I Improve Efficiency in my Geothermal Greenhouse?
Many traditional greenhouses are built to allow some air leakage to permit dangerous combustion fumes to escape, but geothermal heat doesn’t produce fumes, whether the heat comes from the ground itself or from underground wells. The means you can (and should) trap every bit of heat possible to keep your space toasty and comfortable. Geothermal heating is most efficient in a tightly sealed, well-insulated environment. Using a double wall film for your clear walls and sides provides the air gap that’s so critical for insulation.
When using a heavy-duty yet highly emissive film like BTL Liners’ ArmorClear for a double-wall design, the insulation value is often even higher than what’s offered by polycarbonate panels or glass.
