Types of earth-coupling loops

Three popular earth-coupling methods are most commonly employed throughout the geothermal industry.

All three options take advantage of the virtually limitless renewable energy that the earth provides. Each of these three methods have advantages and disadvantages, they are discussed below. To best understand theses options first consider the general approach to taking energy from OR returning energy to the earth. During the winter months we extract stored solar energy that resides in the earth. Approximately 50% of the solar energy that strikes the earth is stored in the waters of the earth. In the summer the relatively cool earth serves as a convenient sink for the excess energy from our homes and buildings.

Closed Loops, either horizontal or vertical (as shown) depend upon an antifreeze solution being returned to the earth and exchanging energy from the average New England earth temperatures of 50°F – in winter, a cold 30°F return solution will make the earth energy flow towards the well bore (CONDUCTIVE FLOW), warming the solution. The opposite energy flow occurs in the summer.

NOTES

Standing Columns, likewise, take advantage of the conductive heat transfer, but also augment their energy transfer capability by simply moving small amounts of stable earth temperature(50°F) water, “ADVECTIVE” flow. This stable temperature water is, typically located only 40-50 feet away from the bore.

Open to Re-circulation earth coupling methods simply take advantage of the stable ground water temperatures, within rock fractures or in porous earth and depend solely upon an ADVECTIVE flow into the borehole. High yield wells and a responsible method of retuning the water to the earth is required. This method is also known as a “doublet” earth coupling. As geothermal heat pump application grows each of these generalized methods have developed variants. This technical bulletin reviews the industry validated methods evaluated by third party agencies. These methods are available through the established Heating Ventilating & Air Conditioning (HVAC) infrastructure in the US and internationally. The International Standards Organization (ISO) has taken responsibility to evaluate geothermal heat pumps in its “standard ISO 13256”. Previously, the Air conditioning & Refrigeration Institute ( ARI), in the USA, had that responsibility. Today, ISO and ARI are overlapping with ISO taking the lead.

METHODS of GEOTHERMAL EARTH COUPLING

Estimated costs for complete earth coupling systems are typical and can be relatively ratio’d as material prices and location change. Note these typical costs relate to “tons” – a ” ton” is a nominal 12,000 BTU/Hr The average 1,800 – 2,500 square foot home is typically in the three (3) to five (5) ton range.