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.
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.
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.
Heating & Cooling
A GAHT™ system also allows the greenhouse to be ‘self-heating.’ At night or on cold days, the GAHT™ system circulates air through the soil again. The warmer soil now heats the air. Warmer air is exhausted back into the greenhouse, providing low-cost, sustainable heating. When the greenhouse heats up during the day, the GAHT™ system draws the hot air from the greenhouse underground. The cooler soil absorbs thermal energy from the air. The air is then exhausted back into the greenhouse cooler and drier.
A GAHT™ system provides air circulation when outside temperatures are either too warm or too cold for standard ventilation by recirculating air (and heat) through the soil.
As hot humid air is circulated underground during the day, it cools and reaches the dew point. Water vapor condenses and percolates into the soil through perforated pipes. The exhausted air is cooler and drier, helping reduce the risk of greenhouse pests and diseases.
Renewable Climate Control
Because the source of heating is the sun, a GAHT™ system allows for the greenhouse to harness a natural greenhouse effect, storing heat in the soil for heating as it is needed.
Purchase Commercial GAHT™ Plans
Commercial GAHT™ System Design
For commercial greenhouses, Ceres provides in-depth evaluation and engineering for your high-performance GAHT™ system.
Our Commercial GAHT™ Services Include:
- 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.
- Finalized GAHT™ plans showing design and pipe layout
- Materials list for final design
- Installation instructions
- Unlimited phone support during installation
Price: Depends on project size and complexity.
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.
To date we have never installed a house GAHT™ system. This does not mean it is not possible. We just have not installed one. Before considering this option there are two concerns you should be aware of:
Radon can be tested. And even if there is radon, it is more significant to watch the rate at which it accumulates. In the worst case scenario, if radon is detected the GAHT™ system can always be shut off.
According to studies that were performed by the University of Minnesota on several GAHT™ systems where mold was tested no elevated spores were detected. It is important to keep in mind this is one study, and they were conducted on greenhouses and not homes.
When trying to mitigate mold in the home you could use a filtration system with a UV lamp. It is important to look at ducting system- how to get air through the system. We can help with the design of a new system, but it is harder to work with existing ones.
Understanding these precautions is necessary if you decide to try this system on a house. Please consult us if you are thinking of a house GAHT™.