Novel instruments and methods to estimate depth-specific thermal properties in borehole heat exchangersShow others and affiliations
2020 (English)In: Geothermics, ISSN 0375-6505, E-ISSN 1879-3576, Vol. 86, article id 101813Article in journal (Refereed) Published
Abstract [en]
Standard thermal response tests (TRT) are typically carried out to evaluate subsurface thermal parameters for the design and performance evaluation of borehole heat exchangers (BHE). Typical interpretation methods apply analytical or numerical solutions, which assume that the ground is homogeneous, isotropic and infinite. However in reality, the underground is commonly stratified and heterogeneous, and therefore thermal properties might significantly vary with depth. Thus, novel instruments and methods are necessary to characterize thermophysical properties along the BHE. In this study, two novel in-borehole temperature measurement instruments, Geoball and Geowire, are assessed during the performance of a distributed TRT (DTRT). The latter is evaluated in comparison to the widely used fiber optical thermometers. Our results suggest that both novel instruments have several advantages. For instance, both devices are able to instantaneously measure temperature with a higher spatial resolution. In addition, our study evaluates two methods to estimate depth-specific thermal conductivities: (1) a computer program based on infinite line source (ILS) approach and (2) a recently suggested inverse numerical procedure. For the latter less data is required, while demonstrating an accurate resolution to even detect thin conductive geological layers. Moreover, the average value of the depth-specific local effective estimates for both methods is significantly close to the effective subsurface conductivity of 3.20 W/m-K calculated based on standard TRT: 1.27 % below for the computer program and 0.28 % below for the numerical procedure.
Place, publisher, year, edition, pages
Elsevier, 2020. Vol. 86, article id 101813
Keywords [en]
Ground source heat pump (GSHP), Borehole heat exchanger (BHE), Distributed thermal response test (DTRT), Layered subsurface, Thermal conductivity, Energy efficiency
National Category
Energy Engineering
Identifiers
URN: urn:nbn:se:kth:diva-275601DOI: 10.1016/j.geothermics.2020.101813ISI: 000534152600026Scopus ID: 2-s2.0-85078718113OAI: oai:DiVA.org:kth-275601DiVA, id: diva2:1436721
Note
QC 20200608
2020-06-082020-06-082024-03-15Bibliographically approved