Converting an Existing Greenhouse to Geothermal Heating

Most of the material on the topic of geothermal greenhouse design, focuses solely on building new structures from scratch. However, a lot of the interest in geothermal heating for greenhouses comes from owners who already have dozens to hundreds of structures they need to heat. It’s not feasible to tear down these valuable and functioning structures and completely redesign them from scratch just to switch heating systems. The good news is that there’s no need to go that far. You can modify any greenhouse to rely on geothermal heating and get a reasonable return on your investment with a few years of operation, even in a cold climate.

Consider Cascade System

If you’re already going through the work to install geothermal heating, consider setting up a cascade system as well. Since there’s no need to spend as much on greenhouse construction, some of the funding can go towards small-scale power generation units and batteries. This will allow you to cut costs on running blowers or lights, or at least have a backup source of power in an outage. In addition to heating the growing space, you might also redirect some of the heat to drying and dehydration units for food processing and long-term storage. Think outside the box and look for potential secondary uses for your heat and power to make a geothermal system as valuable as possible to your business.

Locate the Ground Loops

One of the big challenges of adding a geothermal system to an existing farm or business is finding enough open space for digging or drilling the ground wells. Direct water systems rely on lakes or springs, but ground-to-air and direct air systems rely on deep tunnels or long pipes that take up acres of ground. Many large greenhouses are surprised to find they may need 3 acres or more of open ground to dig up in order to install a horizontal pipe system. Going straight down reduces the space needed, but depth is limited for proper air exchange and these vertical wells are far more expensive to drill than horizontal installations. Regardless of the style you choose, you’ll need to set aside plenty of space and may need to take down a few structures to clear enough room out for the geothermal excavations. Once the wells or pipes are in place, you should be able to use that land again while leaving it partially accessible for repairs.

Find a Hot Water Source

Interested in the low-cost option of circulating naturally heated water through your greenhouse? Then you’ll need to be located near an existing source to take advantage of this system. Natural hot springs are relatively rare, but there are some man-made sources of hot water that can work just as well. Discharge water, from manufacturing or industrial uses that comes out over 300 degrees F, is ideal for circulation through greenhouse radiators; even if it’s not safe for direct exposure to the soil or plants. While this isn’t strictly a geothermal system since the earth’s not supplying the water, it’s a modified form of the same heating process that can make good use of hot wastewater available near the greenhouses.

Maximize Nearby Wind Breaks

There’s little point in moving each greenhouse just to excavate below them and bury them partially in the soil. While this is a great idea for increasing the insulation value of a new greenhouse, it’s not worth the cost and work to renovate an existing structure that’s in good shape. Instead, look for ways to add windbreaks around the exteriors of the buildings instead. If there’s bare ground, use a ripping plow and moldboard to create small mounds of dirt a few feet high and plant them with native shrubs and sturdy trees. This will prevent wind from accelerating heat loss, especially at night and on cloudy days.

Recover the Structure

Most older greenhouses deserve a new cover before being put into new use with an improved heating system. This eliminates the need to go over the existing film to try and patch every hole, crack, or tear that’s developed over the years. If you’re already in need of an upgrade, consider choosing a more durable film fabricated with HDPE and LDPE. Look for a woven product that is reinforced to better resist the constant tugging of the wind and gravity. Not only will this prevent tears and wear holes, it also reduces the amount of stretch and sag in the film. Many greenhouse owners are familiar with the process of re-tightening sections of film on a greenhouse every few months after the initial installation. Woven films don’t stretch as easily, ensuring there’s only one installation process with no need for touch-ups. ArmorClear meets all of these requirements and more.

Try Some Thermal Testing

Still trying to figure out what temperatures you can expect from geothermal heating in your greenhouse? Crop selection and profit forecasting is tricky when you can’t determine how warm you’ll be able to keep the space. Thermal testing is the best way to both estimate the heat holding capacity of the structure and determine where it needs improvements. Infrared cameras in particular will pinpoint where your heat is escaping so you address those areas.

Conclusion

Geothermal greenhouses help eliminate a lot of the problems that make it hard to run a profitable business over the winter in a temperate climate. With a steady supply of heat coming directly from the earth itself, these heating systems reduce the costs, emissions, maintenance requirements, and other issues common to greenhouse management in winter. Even if you only live in a climate where fall and spring growing is profitable enough to cover the costs of supplemental heating, geothermal units are the best option for achieving your goals. You’ll get a long-term supply of heat that won’t need alterations in the next few decades to keep up with changing regulations regarding furnaces and boilers.


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