Greenhouse Subterranean Heating and Cooling System (SHCS): The Climate Battery Explained

Today you're going to learn about the SHCS — short for Subterranean Heating and Cooling System, also called the Climate Battery.

It is an innovative approach to solar greenhouse heating and cooling that uses the physics of phase change for heat exchange. This proven system can heat your greenhouse for operating costs as low as 7 cents per square foot per year — in Colorado Ag Zone 4. With this technique, supplementary heating and fan cooling costs are often entirely eliminated.

The SHCS System Explained

Using research from Canadian government studies, Jerome Osentowski of the Colorado Rocky Mountain Permaculture Institute was among the first to implement this approach commercially. The system has since been built by hundreds of greenhouse growers across North America and Europe.

The approximate material cost is about $1 per square foot of greenhouse. You can get that down to 50 cents if you have fans, thermostats, and barrels on hand. The system pairs particularly well with the other low-cost methods in the complete cheap greenhouse heating guide → — combine the SHCS with bubble wrap insulation → and water barrel thermal mass for a comprehensive year-round system.

Phase Change: The Physics Behind the System

What drives the SHCS is the physics of phase change — from liquid to vapour and back again. The system moves heat from one place to another, functioning as a simple natural refrigeration system.

A typical 1,200 square foot greenhouse needs only the equivalent equipment and running costs of a single household refrigerator.

The SHCS design forces vapour to condense by slowly circulating all the warm, moist daytime greenhouse air underground, where it is always cooler than the greenhouse air. The solar heat — and the chemical heat released by plant photosynthesis — that was required to evaporate the moisture is forced into the soil when the vapour condenses.

By inducing this dewpoint condition in the greenhouse soil, the plant roots are constantly bathed in warm, moist conditions — ideal for growth. The space is then heated by the solar heat radiating back out of the warmed soil under the greenhouse overnight.

How Daytime Heat Storage Works

A small fan is activated by a thermostat set approximately 20°F higher than the soil temperature (typically in the 75–80°F range). The fan activates as the sun heats the greenhouse, moving solar-heated air underground through the buried pipe network.

The entire air volume of the greenhouse moves underground a minimum of 5 times per hour. The soil underground is always cooler than the air, so both regular heat conduction and the dewpoint phase-change effect cause the hot, moist greenhouse air to deposit heat and moisture into the subsoil as it passes through.

The air enters the pipe system hot and moist, and returns to the greenhouse cooler and drier — having left its stored energy in the soil for later retrieval.

Daytime Cooling Effect

Through heat conduction and phase-change condensation underground, the air returning to the greenhouse is typically 30°F cooler than when it left. The drier returning air can also absorb more moisture from the plants and soil above ground, providing evaporative cooling in addition to the temperature drop.

Some Colorado greenhouses with well-designed SHCS systems require no exhaust fans at all. One system built in Colorado was regularly cooler inside during midsummer 105°F days than it was outside — with only the small SHCS fan running. Passive ventilation handles the rest.

Night-Time Space Heating

By storing the day's excess solar energy underground, the warm soil becomes the night-time heat source. Only the above-ground air needs to be reheated as it cools overnight.

A second thermostat activates the same fan when air temperatures drop to the set minimum. The cool greenhouse air is circulated back underground, where it extracts the heat stored during the day and returns warm. This is the exact reverse of the daytime heat storage cycle — same fan, one additional thermostat.

Well-designed Colorado SHCS greenhouses maintain Mediterranean conditions year-round without supplementary heating. Figs, citrus, and other warm-climate plants grow successfully in Ag Zone 4 with no additional heat input beyond the SHCS system.

Equipment and Materials List

For an SHCS build you will need:

• 4" corrugated perforated ADS drainage tubing — approximately 6 linear feet per 4 square feet of greenhouse floor area. Use multiple short runs rather than one long tube — this distributes airflow evenly throughout the soil.
• 55-gallon plastic drums and 12"–18" ADS culverts — to serve as plenums connecting the tubes to the fan. One plenum per fan inlet, one per exhaust location.
• Inline fan — one per 1,200 square feet of greenhouse. Sized to move the entire greenhouse air volume underground at least 5 times per hour. Minimum CFM = greenhouse volume ÷ 12. Check Grainger.com for inline fans in 6"–14" diameter.
• Two adjustable thermostats — one for daytime heat storage activation (30–100°F range with remote sensing), one for night-time heat recovery. Line voltage models for direct fan control.
• Trenching equipment — a 6" trencher for trenchable soil, or a mini-excavator contractor for harder soils. Tubing is buried and backfilled one layer at a time.
• Jigsaw or flycutter — for cutting holes in barrels and culverts to accept the tubing.

Before building, start with the cheaper insulation steps — bubble wrap glazing → and draught sealing — to reduce the heating load the SHCS needs to manage. A well-insulated greenhouse needs a smaller, cheaper SHCS system.

Frequently Asked Questions

How much does an SHCS climate battery cost to build?

Approximately $1 per square foot of greenhouse floor area in materials. A 300 sq ft greenhouse costs roughly $300 in materials. You can reduce this to $0.50/sq ft if you already have fans and thermostats. The system has essentially zero ongoing running costs — the fan draws very little electricity, comparable to a low-energy LED bulb running continuously.

Does the SHCS work in cold climates?

Yes — it was developed and proven in Colorado Ag Zone 4, where winter temperatures regularly fall well below freezing. Jerome Osentowski documented maintaining Mediterranean growing conditions year-round, growing figs and citrus without supplementary heating. The system's effectiveness scales with how much solar heat the greenhouse captures during the day, not with outdoor temperatures directly.

How deep do the SHCS pipes need to be buried?

Typically 1.5–2.5 feet below the greenhouse floor. The key requirement is that the soil at this depth is consistently cooler than the daytime greenhouse air temperature — which is nearly always true. Deeper burial increases the thermal mass available but also increases excavation cost and complexity.

Can I combine the SHCS with other greenhouse heating methods?

Yes, and this is recommended. The SHCS works best as the primary system, supplemented by bubble wrap glazing insulation (reduces heat loss by 30%), water barrel thermal mass (adds overnight buffer), and a thermostatted electric heater as emergency backup for extended cold periods. See the complete greenhouse heating guide → for how these methods combine.