Ground to Air Heat Transfer (GAHT™) Systems

Renewable climate control allows a greenhouse to be ‘self-heating’

A GAHT™ system allows the greenhouse to provide its own heating and cooling using the energy of the sun, and the soil underground. The result is a renewable climate control system that both heats and cools the greenhouse at a fraction of the cost of traditional HVAC.

Ceres Ground to Air Heat Transfer System (GAHT)Ceres' GAHT System
“In the past week the GAHT™ system has been keeping the greenhouse to a minimum of 40°F while the outdoor temps have been anywhere from -10 to – 25°F. The “thermal bubble” beneath the greenhouse has been our biggest energy source, and that has been fueling us adequately.”
DavidCeres Greenhouse Owner, Wellsboro PA

How It Works

GAHT™ systems provide energy-efficient climate control by using the mass of soil underground. Often called a ground to air heat exchanger or climate battery, GAHT™ systems serve four critical functions…

During the day, the fan draws hot air from the greenhouse through a manifold of pipes buried underground. This cools the greenhouse, and simultaneously heats the soil. When the greenhouse needs heating during cold periods, the GAHT™ system draws heat back up from the soil, creating warm air to heat the greenhouse. In other words, a GAHT™ system stores the heat from the greenhouse in the soil underground. The soil acts as thermal mass, helping regulate the air temperature of the greenhouse.

A major part of the cooling process during the day is the role of water vapor. When the greenhouse warms up during the day, evaporation occurs and the humidity rises. When the GAHT™ system circulates air underground, the air cools and reaches the dew point. Water is forced to condense. Due to the energy transfer of phase changes, this further cools the air. The result is cooler, drier air exhausted back into the greenhouse. This both helps keep the greenhouse cool during the day, and lowers the risk of pests and disease issues (usually caused by high humidity).

By recirculating air (and heat) through the soil, a GAHT™ system provides air circulation when the outdoor temperatures are too warm or cold to allow for standard ventilation. This accelerates photosynthesis, and reduces the risk of molds, pathogens, pests and diseases, helping create an healthy abundant year-round environment.

Though GAHT™ systems use small fans to circulate air, these have a very low power draw. The source of heating is the sun, a free renewable energy source. A GAHT™ system allows the structure to take advantage of the natural greenhouse effect (how greenhouses trap thermal energy) storing heat in the soil until it is needed for heating.

Download GAHT Brochure

Engineered Performance

GAHT™ systems are a ground to air heat exchanger, a system often referred to as a ‘Climate Battery.’ Ceres Greenhouse Solutions is an industry leader in greenhouse heat exchangers, having designed and installed more systems than any company worldwide. Ceres’ GAHT™ systems maximize heat transfer to the soil, increasing the heating and cooling potential of the system and making it one of the most cost-effective climate control solutions for residential and commercial greenhouses alike.

*Below, you can see how a GAHT™ System functions throughout the day. Despite outdoor lows of 7°F, a greenhouse with GAHT™ system maintains 40°F indoor temperatures without any back-up heat, and does not overheat the following day.

See GAHT Performance Graph

Residential & Commercial GAHT™ Plans

Climate batteries and GAHT™ systems are deceptively simple systems. A couple fans, some pipes buried underground… what is so complicated? In actuality, these systems depend on a careful balance of airflow, pipe diameter and pipe spacing in order to be effective heating / cooling systems. Our goal is to help clients design and install the most cost-effective and energy-efficient systems for their greenhouse and climate.

Ceres GAHT™ plans package includes:

  • Customized layout of GAHT™ pipe system specified for your size greenhouse
  • Materials list for all parts and sourcing information for necessary components
  • Step-by-step installation instructions with pictures, explaining underground install and how to install and wire fans and thermostats
  • 1 hour of phone support for installation assistance / trouble shooting

Cost: $595

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For commercial greenhouses over 2,000 ft2, Ceres provides an in-depth evaluation of and engineering of a high-performance GAHT™ system. Includes:

  • 1 hour initial design consultation to learn growing goals and greenhouse design
  • 2-3 Layouts of possible GAHT™ system configurations plus rough estimated pricing for each. Final layout depends on greenhouse configuration and floor plan.
  • Customized design and layout of best possible configuration
  • Customized electrical layout and wiring diagrams, considering electric requirements, greenhouse design and electric supply

Plus:

  • Finalized GAHT plans showing design and pipe layout
  • Materials list for final design
  • Installation Instructions
  • Unlimited phone support during installation

Cost: $1,500

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Frequently Asked Questions

“Geothermal” is a broad term, meaning using heat from the earth. GAHT™ systems do use the stable temperatures of the soil, however they are very different systems than geothermal heat pumps, often called “geothermal systems” for short. A geothermal heat pump incorporates a refrigeration cycle and circulates a fluid underground. They are much more complicated and expensive systems than GAHT™ systems. GAHT™ systems, in contrast, simply circulate air and bury pipes relatively shallow, up to 4’ underground.

Ceres Ground to Air Heat Transfer (GAHT™) system is a type of ground to air heat exchanger. Over the years, these have gone by many names including Climate Batteries, coined by Jerome Osentowski and Michael Thompson of the Central Rocky Mountain Permaculture Institute (CRMPI). GAHT™ systems and Climate Batteries use the same concepts, with some slight differences in design and air flow rates. Another similar concept is earth tubes. These use one-way air flow: they draw air in run it underground and pump it into the structure.GAHT™ systems, in contrast, are a closed loop.

The pipes of a GAHT™ system have small perforations so as water condenses underground, it drains out into the soil. This also helps reduce mold issues, which have not been reported in years of testing.

Typically, pipes are buried up to 4’ underground. This can vary by area; the goal is to bury pipes deep enough to reach stable soil temperatures. We additionally insulate around the perimeter of the greenhouse to create an insulated pocket of soil beneath the structure.

In locations where the water table is higher than 4’, it is challenging to integrate a standard GAHT™ system. Other heat storage methods, like phase change material can be used to make your greenhouse as energy-efficient as possible. Please contact us about your options.

The cost of a GAHT™ system depends on the size of your greenhouse. Typically, residential GAHT™ systems (under 1,000 sq. ft.) cost between $2,000-5,000. Larger commercial greenhouses and school greenhouses typically cost $5,000-$15,000 depending on size.

Ceres Greenhouse Solutions

303.495.5006
4760 Walnut St., Suite 106
Boulder, CO 80301
United States