Colloquium 2016: Assessment of subsurface thermal conductivity for geothermal applications

Raymond, Jasmin

doi:10.1139/cgj-2017-0447

Cited by 19 publications

(42 citation statements)

References 103 publications

(138 reference statements)

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“…The subsurface thermal conductivity can be deduced with different approaches, presented below in order of increasing reliability and representativeness: laboratory analysis on samples collected from outcrops, drilled cuttings or cores; passive in situ analysis based on the interpretation of geophysical signals; and active heat transfer experiments conduct in the field such as thermal response tests (TRTs; Raymond, 2018). The cost of each method generally increases with reliability and representativeness.…”

Section: Accepted Manuscriptmentioning

confidence: 99%

A workflow for bedrock thermal conductivity map to help designing geothermal heat pump systems in the St. Lawrence Lowlands, Québec, Canada

Raymond

Bédard

Comeau

et al. 2019

Science and Technology for the Built Environment

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An accurate knowledge of the subsurface thermal conductivity is essential to design geothermal heating and cooling systems, more specifically ground-coupled heat pumps.The subsurface thermal conductivity has a direct impact on the length of vertical ground heat exchangers needed to fulfill building energy needs. However, mapping the distribution of the subsurface thermal conductivity is a significant challenge due to the ground heterogeneity and the limited radius of influence associated to thermal A c c e p t e d M a n u s c r i p t conductivity assessment methods. Data from 79 thermal response tests, 90 thermal conductivity analyses conducted in the laboratory and geophysical well logs from 72 exploration wells were combined and analyzed all together in an attempt to map the bedrock thermal conductivity distribution of the St. Lawrence Lowlands, Québec,Canada. Results from laboratory and well log analysis were adjusted for field scale effects using thermal response tests to properly define a statistically reliable thermal conductivity for each thermostratigraphic unit of this sedimentary basin. The thermal conductivity obtained from thermal response tests and adjusted laboratory analyses was interpolated with sequential Gaussian simulations to generate a 2D bedrock thermal conductivity map, which can be used by geothermal system designers to better understand the geothermal heat pump potential of the

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Section: Accepted Manuscriptmentioning

confidence: 99%

A workflow for bedrock thermal conductivity map to help designing geothermal heat pump systems in the St. Lawrence Lowlands, Québec, Canada

Raymond

Bédard

Comeau

et al. 2019

Science and Technology for the Built Environment

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“…The thermal conductivity assessments were made with two different methods: (1) a needle probe for hard rocks [12,[28][29][30] and (2) the modified transient plane source (MTPS) method for friable rocks [30][31][32]. The KD2 Pro unit [33], part of a standardized method under the ASTM D5334 norm, was used for the needle probe analysis with gabbro samples, while the C-therm heating plate following the ASTM D7984 norm was used for the MTPS analysis with shales and calcarenites [34].…”

Section: Laboratory Measurement Of Thermal Conductivitymentioning

confidence: 99%

Long-Term Temperature Evaluation of a Ground-Coupled Heat Pump System Subject to Groundwater Flow

et al. 2019

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The performance of ground-coupled heat pump systems (GCHPs) operating under significant groundwater flow can be difficult to predict due to advective heat transfer in the subsurface. This is the case of the Carignan-Salières elementary school located on the south shore of the St. Lawrence River near Montréal, Canada. The building is heated and cooled with a GCHP system including 31 boreholes subject to varying groundwater flow conditions due to the proximity of an active quarry being irregularly dewatered. A study with the objective of predicting the borehole temperatures in order to anticipate potential operational problems was conducted, which provided an opportunity to evaluate the impact of groundwater flow. For this purpose, a numerical model was calibrated using a full-scale heat injection test and then run under different scenarios for a period of twenty years. The heat exchange capacity of the GCHP system is clearly enhanced by advection when the Darcy flux changes from 6 × 10−8 m s−1 (no dewatering) to 8 × 10−7 m s−1 (high dewatering). This study further suggests that even the lowest groundwater flow condition can be beneficial to avoid a progressive cooling of the subsurface due to the unbalanced building loads, which can have important impacts for design of new systems.

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“…The same field test methodology was applied to both sites, but the heat injection rate was adapted according to heating cable design to achieve a low-power requirement. [26]).…”

Section: Field Test Methodologymentioning

confidence: 99%

“…The heat injection rate of heating cables used for previous tests varied from 20 to 40 W•m −1 [23,24] and the required power of less than 1 kW was supplied by connecting the TRT unit to the electrical grid [24]. Tests with a continuous heating cable wete achieved in boreholes having a depth of approximately 30 m, while boreholes with more than 100 m in length have been the subject of tests with heating sections to keep a low power requirement [26].…”

Section: Introductionmentioning

confidence: 99%

Distributed Thermal Response Tests Using a Heating Cable and Fiber Optic Temperature Sensing

et al. 2018

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Thermal response tests are used to assess the subsurface thermal conductivity to design ground-coupled heat pump systems. Conventional tests are cumbersome and require a source of high power to heat water circulating in a pilot ground heat exchanger. An alternative test method using heating cable was verified in the field as an option to conduct this heat injection experiment with a low power source and a compact equipment. Two thermal response tests using heating cable sections and a continuous heating cable were performed in two experimental heat exchangers on different sites in Canada and France. The temperature evolution during the tests was monitored using submersible sensors and fiber optic distributed temperature sensing. Free convection that can occur in the pipe of the heat exchanger was evaluated using the Rayleigh number stability criterion. The finite and infinite line source equations were used to reproduce temperature variations along the heating cable sections and continuous heating cable, respectively. The thermal conductivity profile of each site was inferred and the uncertainly of the test was evaluated. A mean thermal conductivity 15% higher than that revealed with the conventional test was estimated with heating cable sections. The thermal conductivity evaluated using the continuous heating cable corresponds to the value estimated during the conventional test. The average uncertainly associated with the heating cable section test was 15.18%, while an uncertainty of 2.14% was estimated for the test with the continuous heating cable. According to the Rayleigh number stability criterion, significant free convection can occur during the heat injection period when heating cable sections are used. The continuous heating cable with a low power source is a promising method to perform thermal response tests and further tests could be carried out in deep boreholes to verify its applicability.

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Colloquium 2016: Assessment of subsurface thermal conductivity for geothermal applications

Cited by 19 publications

References 103 publications

A workflow for bedrock thermal conductivity map to help designing geothermal heat pump systems in the St. Lawrence Lowlands, Québec, Canada

A workflow for bedrock thermal conductivity map to help designing geothermal heat pump systems in the St. Lawrence Lowlands, Québec, Canada

Long-Term Temperature Evaluation of a Ground-Coupled Heat Pump System Subject to Groundwater Flow

Distributed Thermal Response Tests Using a Heating Cable and Fiber Optic Temperature Sensing

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