Moonshot Farm has two 3000 square foot greenhouses where flowers are grown directly in the floor soil. (Courtesy photos)
Joanne Coons
A geothermal system was installed to maintain the proper temperature to grow the flowers.
Sometimes proven technology is the solution to doing things a little differently and a little better. Applying ground-source heat pump (GSHP) technology to heating and cooling long tunnel greenhouses provides a low-cost solution to maintain the required temperature needed to keep plants thriving all year long.
One such example of using GSHP technology is the Moonshot Farm (which grows cut flowers) in East Windsor, New Jersey. Moonshot wanted to expand to a second 3000 square feet of growing space using a standard Quonset hut-type double-layer poly sheet construction with an air gap rated at R1.8. There are eight-foot-wide sliding doors on both ends that are very modestly sealed. There is no additional insulation; flowers are grown directly in the floor soil. In the existing “propane twin” long tunnel greenhouse, keeping the temperature to a nominal 50°F during 2021-2022 used approximately $6,800 of propane. This is not sustainable! There has to be a better way.
The owners became aware of the USDA Rural Energy for America Program (REAP) grant that could defray 25% of the cost of qualifying renewable energy systems. Moonshot Farm reached out to James Thomas of Thomas Geothermal Engineering (TGE) to assess if a geothermal heating and cooling system was feasible, could substantially reduce its energy bill, and be a strong enough case to be awarded the REAP grant. The owners also thought a green energy system would be a strong selling point to its customer base. A simple calculation quickly revealed that a geothermal system could indeed be within reach for this application and provide the annual heating load. Moonshot was awarded a grant on July 7, 2022 at which time TGE commenced a detailed design and ordering of materials.
The temperature range for the cut flowers is between 55-70°F. The winter design temperature for the GSHP at this location is 15°F. This would require a 10.86-ton design load, so two WaterFunace Series 5, two-speed six-ton geothermal units would be needed. (The six-ton unit uses two phase wire which the farm is wired for, not a three- phase commercial wiring.) The water pump is a Geo-Flo NP Multi flow center with a Grundfos Magna3 variable speed pump. There is a 1.5-acre open pasture next to the greenhouse that was chosen for a horizontal loop. The loop included seven six-foot-deep, 300-foot-long trenches using Twister pipe by Agreenability which increases pipe surface area and increases heat transfer which shortens the length of pipe needed. (Less drilling or digging, less pipe needed). The two units were arranged on each end of the tunnel to help balance the temperature. DuctSox lightweight fabric duct was chosen to distribute the forced air evenly down each trunk. Since this was expected to be an unbalanced heating dominant application, the system will capture heat and recharge the ground particularly during summer months. The system can also be used as low-cost compressor-less cooling as needed. Some A/C was used even on freezing winter days when the tunnel would otherwise warm up to 90°F; winter crops need 70°F or less. In accordance to the USDA grant the installed system must be monitored for three years after installation to prove its efficiency.
A geothermal system was installed to maintain the proper temperature to grow the flowers.
Financials: The USDA grant has been expanded from the 25% in 2022 to 40% as of 2023. The Inflation Reduction Act will provide a 30% incentive, and if there is domestic content, the rebate will increase to 40%. The one-year electricity use for the GSHP hoop house is $2080. The installation cost was $94,673. The cost of propane to heat the tunnel is $6774 (remember there is a propane twin to measure and compare the GSHP hoop house). At the 2024 incentive rate, reducing the initial cost by 80% (USDA 40% and IRA 40%) the installation cost adjusts to $18,953. If you divide that by the cost savings of propane which is $4,694, that gives a return on investment of 4.03 years. As a business, the remaining investment after funding can be depreciated over five years, so this model is a no-brainer, as they say. It is worth mentioning pricing, grant application and processing and payment to the installer needs to be coordinated and may require large upfront costs before payback or additional loans to bridge the payback period. If you were to add a solar photovoltaic system to power the farm’s electricity, that system would qualify for the same financial incentives.
twin long tunnels
Some of the other benefits of this system are the ability to grow fruits, vegetables and plants year-round locally thus further reducing the farm’s carbon footprint. Produce could be fresher; crops won’t be as weather-dependent i.e., reducing crops damaged by frost, floods or heat waves.
Does this sound like an award-winning design? If you said yes, you would be correct! James Thomas won the 2023 IGSHPA (International Ground Source Heat Pump Association) Commercial Innovation Award and is the finalist for NY-GEO Top Job Award.
If you know a farmer or organized community gardens, please share this information with them.
Joanne Coons teaches at Hudson Valley Community College, TEC-SMART facility teaching. Locally, Joanne advocates for sustainability as a member of the Town of Clifton Park’s GREEN (Government Re-Thinking Energy & Environment Now) and is active in NY-GEO and NYSES. Prior to her current endeavors, she taught high school science for 28 years.
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