Abstract
The performance of ground heat exchanger systems depends on the knowledge of the thermal parameters of the ground, such as thermal conductivity, capacity, and diffusivity. The knowledge of these parameters often requires quite accurate experimental analysis, known as a thermal response test (TRT). In this paper, after a general analysis of the various available types of TRT and a study of the theoretical basics of the method, we explore the perspective of the definition of a simplified routine method of analysis based on the combination of a particular version of TRT and the routine geotechnical tests for the characterization of soil stratigraphy and the ground characteristics. Geotechnical analyses are indeed mandatory before the construction of new buildings, even if limited to 30 m below the ground level or foundation base when piles are needed. The idea of developing TRT in connection with geotechnical test activity has the objective of promoting the widespread use of in situ experimental analysis and reducing TRT costs and time. The considerations presented in the present paper lead to reconsidering a particular variety of the TRT, in particular, the versions known as thermal response test while drilling (TRTWD) and TRT using heating cables (HC-TRT).
Highlights
Geothermal systems that use ground-coupled heat exchangers (GHEs) and ground source heat pumps (GSHPs) are popular all over the world as a measure for energy saving for heating and cooling purposes
After a preliminary analysis of the recent evolutions of thermal response test (TRT), this study aimed at proposing a method for estimating the thermal properties of soil in a relatively short time and an economical manner, thanks to the conjunction with the geological test already needed for structural purposes
The test period usually advised in the literature is about 50 hours for obtaining an error in the thermal conductivity that is below 10%, as it can be observed in Figure 3, where the evaluation of the thermal conductivity using TRT is reported for two different ground typologies
Summary
Geothermal systems that use ground-coupled heat exchangers (GHEs) and ground source heat pumps (GSHPs) are popular all over the world as a measure for energy saving for heating and cooling purposes. This is mainly true in the case of cold climates, even if the use of GSHPs has been extended to temperate climate conditions too. Different types of heat exchangers can be used, both vertically and horizontally installed. The most common vertical type is the borehole heat exchanger (BHE). The number of boreholes connected to the installed heat pump can vary from one for a residential building to several dozen in case of commercial or large-size buildings
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