Evaluation of temperature profiling quality in determining energy efficiencies of borehole heat exchangers.

Highlights • A methodology for determining the energy efficiency of borehole heat exchangers based on temperature profiling is described. • Temperature profiles over the last 10 years have been analyzed. • The causes of disturbances in the temperature profiles were investigated. • Periodic penetration depth of heat maps and temperature loggings have been compared. Abstract By profiling the natural temperature of borehole heat exchangers it is possible to determine the thermal conductivity λ of the ground using Fourier's law. However, analyses of borehole temperature profiles lead to the conclusion that the profiles differ from the theoretical data. The causes are many, including urban infrastructure leading to ground temperature profiles being heavily distorted. Among factors impacting ground temperature profiles are: buildings, roads, heat pipelines, water pipelines, and sewers. Ground temperature profiles influenced by urban infrastructure are not valid for determining ground thermal conductivity. The aim of the work is to analyze factors influencing temperature logging changes in borehole heat exchangers and their suitability for determining ground thermal conductivity. Based on the temperature logging, the depth of periodic heat penetration is assessed and is compared with the value determined on the basis of the map. It is found that the natural temperature profiles in borehole heat exchangers are only partially suitable for the analysis of the thermal conductivity of rocks. [ABSTRACT FROM AUTHOR]