Thermal comparison of two borehole heat exchangers

Abstract

Consulta en la Biblioteca ETSI Industriales (7779)

[EN] Vertical borehole heat exchangers are one of the most commonly used collectors for ground source heat pumps. This Master¿s Thesis presents an extensive comparison between two different borehole heat exchangers of a ground source installation located in the south of Stockholm, Sweden. A typical U-pipe heat exchanger is compared to a U-pipe heat exchanger equipped with spacers between pipes. The comparison is based on temperature measurements using thermocouples and optical fibre cables. The undisturbed ground temperature was measured before the system started up. Besides, two different periods of measurements were carried out. The first measurements studied the secondary working fluid temperature profiles during 18 days. In the second measurements the temperature profiles of three different flow regimes were analyzed. The ground water flow outside the boreholes was also studied in both measurement periods. Results from the undisturbed ground show that the geothermal gradient appears at half of the borehole length. From the first measurements results it was not possible to determine which collector is better due to uncertainties in the measurement conditions. The second measurement period shows that the extracted heat increases as the flow becomes more turbulent. The typical U-pipe borehole heat exchanger was demonstrated to extract a major amount of heat from the ground although the differences between collectors are not substantially significant.