Abstract
For designing of Ground Source Heating Systems (GSHS) Thermal Response
Tests (TRT) are used for a long time. TRTs generally provide a profound
basis for the final implementation of a GSHS. They obtain the effective
thermal conductivity and thermal resistance of a borehole. Until today
several TRT types have been introduced and defined as Geothermal
Response Test (GRT), Enhanced GRT (EGRT), Constant Heat Flux TRT
(chTRT), Constant temperature (ctTRT ) etc.. These models mainly focus
on closed heat exchangers in shallow boreholes. However, recent
developments in medium depth drilling technologies make deeper boreholes
more economic. Furthermore, advanced methodologies for obtaining thermal
conductivities in deep and open boreholes are progressing. In this
study, we introduce a new simple thermal conductivity obtaining
methodology that can be used for deep and open boreholes. Generally,
TRTs are applied with the circulation of water inside pipes or immersing
probes in water. In case of water circulation in deep boreholes,
different heat flux values will be attributed to different layers.
Moreover, by introducing a constant heat flux similar to conventional
TRT into water-filled boreholes or water-filled pipes, convective
movements of water will occur and thermal conductivities cannot be
obtained. However, immersed probes as a heat source might prevent water
convection cells inside a pipe or a borehole. In deep boreholes, the
heat flux is depended on the thermal conductivity of each layer. Thus,
deep boreholes require a discrete heat introduction into every single
layer of different thermal conductivity in order to keep the temperature
constant. The thermal conductivity of each layer can be approximated and
integrated over the total length of a deep borehole. This effect is
analytically and numerically investigated in this study.