Ground-coupled heat exchanger

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Earth cooling tubes utilize the earth's near constant subterranean temperature to warm or cool air for residential, farm or industrial uses. It is often a viable and economical alternative to conventional heating, cooling or heat pump systems since there are no compressors, chemicals or burners and only require a blower to move the air.

Most systems are usually four inch to eighteen inch diameter, smooth-walled, rigid or semi-rigid plastic or metal pipes, buried six to ten feet underground where the temperature is typically 50-70 degrees year round (in the northern hemisphere). There are basically three configurations, a closed loop design, an open 'fresh air' system or a combination.

With the closed loop system, air from inside the home or structure is blown through a U-shaped loop(s) of typically one hundred to five hundred feet of tube(s) where it is moderated to near earth temperature before returning to be distributed via ductwork throughout the home or structure. Larger diameter tubes need less total length.

The open system draws outside air from a screened intake in the yard through, typically, a hundred or more feet of straight tube into the home. The closed loop system is usually more effective than the open system since it cools and recools the same air.

A combination system can be crafted with unidirectional check valve dampers to allow either closed or open operation depending on the season and/or fresh air ventilation requirements. Such a combo design, even in closed loop mode, could draw a quantity of fresh air when an air pressure drop is created in the house by a fireplace chimney draft or attic fan.

Earth cooling tubes are, by their subterranean nature, usually located to penetrate the wall of a house's basement where they interconnect with a standard system of ventilation ductwork for distribution of the air throughout the home. As such, they may be better suited for new construction than for retrofit into an existing home, especially if there is a limited outside yard space to work with.

The efficiency of earth cooling tubes can vary widely depending on tube depth, climate, soil type, soil moisture content and ground level sun or shade. Generally sandy, dry soil with little or no ground level shade will yield the poorest benefit while dense clay or damp loam with considerable shade should perform well. Careful siting and making provision for adequate soil moisture, perhaps via landscape drainage or soaker hoses could be advisable. Damp soil absorbs and dissipates the warmth drawn off the tubes better than dry soil.

Ground-coupled heat exchanger

One drawback often cited to earth cooling tubes is the possibility of condensation buildup in the tubes and subsequent mold growth. A properly designed system that maintains a constant downward slope from the (upper) warm air intake end to the(lower) cool air outlet end should provide adequate drainage of condensation that can be handled by a floor drain, much like a conventional home air conditioning system. Also, it is important not to use corrugated or ribbed tubing as this would create traps where moisture would assuredly accumulate.

While some possibility of mold growth might still be possible, smooth round tubes should be much easier to clean than conventional rectangular metal ductwork found in the average home or office where mold growth is, of course, a common and accepted problem.

In the context of today's diminishing fossil fuel reserves, increasing electrical costs, air polution and changing climate, properly designed earth cooling tubes present an intriguing alternative for our heating and ventilation needs. Like solar heating, earth cooling tubes let us design and build in harmony with nature to achieve comfortable, clean, cost-effective and renewable homes for the future.