Novel instruments and methods to estimate depth-specific thermal properties in borehole heat exchangers

A Case Study of Thermal Evolution in the Vicinity of Geothermal Probes Following a Distributed TRT Method

“…The results of Pambou et al [28] did not exceed values of around 55 W/m and a temperature increase of 1-2 degrees by applying a relative high heat injection rate due to the system length. Although, a similar heat load was applied, for instance around 1500 W [24], the reached temperatures were distinctly lower than within this study (inlet temperature ≈ 50 • C) due to the system depth. Regarding a further investigation [55], where a similar power load was applied on a 15 m deep helical BHE, relative high temperatures (up to 45 • C) could have been reached.…”

“…Regarding the thermal evolution within the vicinity of the borehole (a 20 cm distance to the helical system) the measured temperatures were 18 degrees less than the inlet temperature and 10 degree less than the outlet temperature, which represents a far more significant temperature decrease within the same borehole as a 2-degree difference within the research of Aranzabal et al [24]. This can be clarified by the different distance from the observer pipe to the geothermal system (20 cm vs. <5 cm) where the heat load was applied and by the much higher temperature gradient, which was achieved within this study.…”

“…Hence, a high resolution was not decisive within their case. Aranzabal et al [24,44] stated that novel instruments, such as the GEOsniff, have various advantages over standard sensors and fiber optics and also regarding the spatial resolution.…”

“…In this study, the rise in temperature close to the BHE was focused within a thermal test. To facilitate temperature monitoring of the ground in the immediate vicinity of the borehole, an additional single-U probe was inserted into the same borehole [23], similarly to the observer pipe applied by Aranzabal et al [24] but within another distance to the system. This proceeding enabled a more ground-layer-dependent temperature measurement [24] than within the percolated helical BHE.…”

Experimental Hydration Temperature Increase in Borehole Heat Exchangers during Thermal Response Tests for Geothermal Heat Pump Design

“…Haranzabal et al [1,12] have tested and compared different sensors for distributed (along the BHE depth) measurements, including submersible sensors and optical fibers, confirming that travelling sensors inside the carrier fluid stream are suitable for temperature measurements along the BHE. Furthermore, according to the literature investigation [1,12] these sensors can assure good spatial accuracy, provided that the sinking speed and sampling time are correctly chosen.…”