Before you undertake the research need to design a cutting-edge sustainable heating system for a greenhouse, you should explore why it’s a valuable technique in the first place. Geothermal heating has been around for decades in its modern form and for millennia in more crude methods. As the name suggests, the heat in the system is provided by the earth. At the surface of the soil, dirt changes temperature rapidly and stays near the ambient air temperature. If you dig down deeper, the temperature rapidly stabilizes and doesn’t change much from around 55 degrees Fahrenheit in most parts of the world. By digging deep wells or using water that’s underground, you can produce heat through the efficient extraction process of the heat pump. If you’re lucky enough to locate your greenhouses near a natural source of heated water, you can even just circulate the water through the space and let heat radiate out. By tapping into a constant source of steady and even heat, you gain many benefits over fossil fuel powered greenhouse heating equipment.
Why Greenhouses Need Heating
Season extension, by trapping heat, is the primary use for most greenhouses. This can be used whether they’re commercial or personal systems. While some greenhouses are built in tropical areas that don’t need the heat, most are located in cool to cold climates. An unheated film greenhouse, even with double layers of a thick film, will only stays a few degrees above the ambient temperature in the winter. Even when all the available heat is trapped from solar radiation during the day, the temperature drops overnight. Heating a greenhouse can allow the structure to grow tender and tropical plants well into the winter and possibly all year round. Yet, traditional furnaces and natural gas heaters are expensive to operate and come with plenty of drawbacks and risks.
Common Sources of Greenhouse Heat
Greenhouse heating has been an option since the invention of the first glass solariums and some old-fashioned methods, like wood-fired boilers or kerosene smudge pots, are still in use. Some of the most common modern and traditional methods for greenhouse heating include:
- Boilers powered by electricity, natural gas, or solid fuels that centralizes heat production and deliver hot water to radiators in each greenhouse to release heat into the air
- Forced air furnaces powered by electricity or natural gas, which can be centralized or installed individually for each structure
- Local space heaters placed in the greenhouses themselves to release warmth directly from electric elements or propane burners
- Passive solar techniques that trap as much heat from the sun as possible and slowly release it over the course of a night.
Issues with Fuel Sources
With so many fuel sources already available and well-tested for greenhouse use, a farmer may wonder why he or she should bother with setting up a geothermal system instead. Unfortunately, all of the heating options listed above come with serious drawbacks. Fossil fuels like propane, natural gas, gasoline, and diesel are unsustainable and contribute high levels of CO2 emissions. 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 of these heating methods tend to fluctuate from year to year. Once you’ve made the initial investment on a geothermal system, the cost to operate it will only very slightly and the variance will only if electricity is required for the system.
The Benefits of Geothermal Heat
Geothermal heating for greenhouses addresses all of the biggest flaws of other heating methods. Aside from the initial investment into design and installation, geothermal systems are very affordable to run on an annual basis. Passive systems have basically no operating costs other than occasional maintenance needs, while active systems still use a fraction of the electricity needed for direct forced air or space heating. It’s a sustainable heating choice because it generates no CO2 or other pollution during operation and minimizes the need for electricity generated in an unsustainable way. You can build geothermal systems in remote areas where there’s no electricity service or delivery for fuel. Maintenance is lower and daily operation is simpler than for other greenhouse heating furnaces, resulting in an easier job for your employees. Since forced air and heat pump geothermal systems only require a relatively small amount of electricity, they’re easy to keep running with a backup generator if necessary. This prevents seasonal storms from freezing your entire crop and causing significant losses during a power outage.
Potential Disadvantages of Geothermal Systems
Despite sounding perfect for greenhouse heating needs, there are a few minor drawbacks to installing a geothermal system. It’s important to address these considerations honestly to ensure the technology is the right fit for your particular greenhouse.
First, geothermal equipment does come with some high upfront installation costs. The heat pumps and blowers used for forced air systems are usually less expensive than similarly sized furnaces, but there’s a lot of cost associated with the extensive drilling and digging needed for the underground wells. Even when you live in an area where you can drill vertical wells relatively quickly, the cost is usually in the hundreds of thousands of dollars for excavation alone. Trying to handle this work in a DIY way, risks a dangerous sinkhole collapse and a system that doesn’t produce enough heat.
Second, these systems only work in certain types of soil. If the greenhouse is located in an area with very loose or sandy soil, the geothermal wells may collapse during or after drilling. There’s also less temperature buffering effect in loose soils, resulting in uneven heating results. Thankfully, most parts of the country that are too sandy for geothermal use are also quite warm and rarely need greenhouse heating.
Finally, the need for electricity to keep heat pumps and blowers working does leave the geothermal system at risk for shutting down during a winter storm. However, it’s easier to use a generator or batteries to backup this kind of heating equipment since it uses only a fraction of the electricity required for electric furnaces or space heaters. There are also passive geothermal heating systems that require no electricity, although they’re much more limited in how much heat they provide and how far it can be moved without fans and blowers.
Now that you’ve compared geothermal designs to other heating options for the commercial greenhouse, you should have a better idea of what will work for you. If you’re considering the installation of a system but worry that your greenhouse isn’t insulated enough to make use of it, consider retrofitting your existing structures with ArmorClear from BTL Liners.
