More than 15 years of mobile Thermal Response Test - a summary of experiences and prospects

The first mobile thermal response tests (TRT) were done in the USA in the year 1995 and in Sweden in early 1996. Reports from the Swedish tests were shared within an energy storage group of IEA (IEA ECES Annex 8) in 1996, and the idea soon spread to many countries. In Germany, first tests were made independently by two groups in 1999 (Sanner et al, 1999). Meanwhile, TRT is a basic tool for in-situ determination of thermal ground parameters, used in most countries where borehole heat exchangers are used, both for ground source heat pump development and for underground thermal energy storage. Knowledge and experience today allow for high accuracy and reliability of the test results. This paper reviews briefly the development of the technology, and gives an overview of the status achieved today, as an update of the last paper of this type from WGC 2005 (Sanner et al., 2005). It then focusses on some misunderstandings of test procedure and in the use of the test results that could be found in reports and commercials. The parameters that can be achieved from a TRT are discussed, in perspective to accuracy and limitations of test evaluation methods. Further applications of TRT to other parameters than just the thermal conductivity of the ground will be listed.