Improvements of U-pipe borehole heat exchangers. Licentiate thesis.

There are approximately 360 000 systems installed in Sweden with a growing rate of about 30 000 installations per year. The most common way to exchange heat with the bedrock in ground source heat pump applications is circulating a secondary fluid through a borehole heat exchanger, a closed loop in a vertical borehole. The fluid transports the heat from the ground to a certain heating and/or cooling application. A fluid with one degree higher or lower temperature coming out from the borehole may represent a 2-3% change in the COP of a heat pump system. This licentiate thesis presents the analysis of several groundwater filled borehole heat exchangers, including standard and alternative U-pipe configurations (e.g. with spacers, grooves), as well as two coaxial designs. It embraces measurements of borehole deviation, ground-water flow, undisturbed ground temperature profile, secondary fluid and groundwater temperature variations.