Vertical borehole systems (simple or double U-tubes)

Vertical borehole systems

These systems are composed of 60 to 150-meter deep vertical boreholes in which plastic (sometimes copper) U-tubes are installed. Since changes of the air temperature has influence on the soil temperature only till depth of about 15 meters, the temperatures of deeper layers depend only on the heat energy flow from the center of the Earth. (In Hungary, for example, the soil temperature at the depth of 100 meters is between 15 and 16°C in general.)

Translations:

A talajhőmérséklet éves vázlatos hőmérséklet-diagrammja - Approximate yearly temperature diagram of soil in Hungary

január - January; április - April; október - October; július - July

In consequence of the above explanation, properly designed vertical borehole systems, thanks to their almost constant temperatures, can serve as very good and stable primary source for the connected heat pump systems. The U-tubes are connetcetd through header pipelines that are layed at depth of 160-180 cm in trenches. Such borehole systems does not have any influence on the surface of the soil.

Adventages:

• in case of a properly sized vertical borehole system there is no need to install any complementary heat source (like gas boiler, etc.) and it will work with high COPs,
• properly installed pipeline systems that are made of high quality plastic, can be operated for a long time with very high reliability, without any leakings. This means that such borehole systems can be installed even under foundations of new buildings,
• heat pump systems with active cooling option can dissipate the extracted from the buildings heat through these pipelines with high efficiency,
• when the pipeline system is ready, the surface can be fully restored. Planting of trees and bushes with strong roots above the pipeline system is not recommended.

Disadventages:

• installation costs are higher in comparison with other primary heat sources,
• such systems cannot get licence for installation in some special areas (protected areas, thermal or other underground waters, special constructions, etc.)
• such systems are not recommended for installation in areas with low thermal conductivity of the soil or where it is too hard to drill the soil.