Abstract
BackgroundBorehole heat exchangers are a growing technology in the area of house/building air conditioning, most of all in northern Europe.MethodsIn order to have a good project, we need to have a reliable value of ground thermal conductivity, which is normally obtained by interpreting the data retrieved by running a thermal response test. Different are the ways of interpreting the data provided by the test (e.g., infinite line source theory, finite line source theory, etc.), and in this paper.ResultsWe will first simulate a thermal response test using finite element subsurface flow system, a heat and flow dynamic simulator.ConclusionsThen, a sensitivity analysis of the effect of the different grout properties on the results of a thermal response test is shown.
Highlights
Borehole heat exchangers are a growing technology in the area of house/building air conditioning, most of all in northern Europe
The thermal conductivity values for all the different layers were used, the ones obtained by running direct sequential simulations on GeoMS and whose calculations were described in the previous paragraph
The shape of the curve is exactly like what we have in the real thermal response test (TRT), but the temperature shows a systematic difference of almost 1°C between the two curves
Summary
Borehole heat exchangers are a growing technology in the area of house/building air conditioning, most of all in northern Europe. In contrast to the northern part of Europe (for example, the Scandinavian regions), the typical shallow ground in the southern part of Europe is not made of rocks (granite, basalt), but it is composed mainly of loose materials (sand, clay, marl, etc.) This fact complicates the application because of drilling issues, the reduced homogeneity of the soil, and lower thermal conductivity. At the current state of technology, the thermal response test (TRT) is the in situ test for the characterization of ground thermal properties with the highest degree of accuracy (Figure 1) It consists of injecting/extracting heat to/from the borehole heat exchanger for a limited time and typically with a constant power flux (Gehlin & Eklof 1996); (Gehlin 2002). The cylindrical ring is composed of several materials; some of them are artificial (bentonite, pipes) and have theoretically constant thermal properties, while others, the natural ones, have variable ones
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