Introduction of the Excitation-Modulated Thermal Response Test (EM-TRT) for the improved Evaluation of Vertical Ground Heat Exchangers

Abstract

Ground-Source Heat Pump (GSHP) systems are crucial for reducing the building sector’s carbon footprint by providing efficient and sustainable heating and cooling solutions. Their performance relies on the ground’s thermal properties at depth, which are identified through Thermal Response Tests (TRTs). These tests are vital for accurately sizing and optimizing the economic efficiency of GSHP systems. However, conventional TRTs are time-consuming, costly, prone to disturbances, and only determine the soil’s average thermal conductivity across the entire borehole depth. Especially in the presence of underground water streams classic TRTs yield insufficient results. In this paper we introduce a new Excitation Modulated Thermal Response Test (EM-TRT), utilizing an Amplitude-Modulated Pseudo-Random Binary Sequence (APRBS) signal. This method significantly shortens test duration and enables the simultaneous detection of different geological layers and estimation of their thermophysical parameters. EM-TRT proves to be highly practical, functioning seamlessly with standard TRT devices without the need for additional equipment. The method is validated with model-generated data, historical TRT measurements, and employed on a dedicated experimental TRT at a geothermal borehole in Austria. EM-TRT provides a robust solution for rapid and accurate geophysical assessments, representing a substantial improvement over traditional methods.