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Borehole

The Experts below are selected from a list of 321 Experts worldwide ranked by ideXlab platform

Göran Hellström – 1st expert on this subject based on the ideXlab platform

  • cfd modelling of natural convection in a groundwater filled Borehole heat exchanger
    Applied Thermal Engineering, 2010
    Co-Authors: Annamaria Gustafsson, Lars Westerlund, Göran Hellström

    Abstract:

    In design of ground-source energy systems the thermal performance of the Borehole heat exchangers is important. In Scandinavia, Boreholes are usually not grouted but left with groundwater to fill the space between heat exchanger pipes and Borehole wall. The common U-pipe arrangement in a groundwater-filled BHE has been studied by a three-dimensional, steady-state CFD model. The model consists of a 3 m long Borehole containing a single U-pipe with surrounding bedrock. A constant temperature is imposed on the U-pipe wall and the outer bedrock wall is held at a lower constant temperature. The occurring temperature gradient induces a velocity flow in the groundwater-filled Borehole due to density differences. This increases the heat transfer compared to stagnant water. The numerical model agrees well with theoretical studies and laboratory experiments. The result shows that the induced natural convective heat flow significantly decreases the thermal resistance in the Borehole. The density gradient in the Borehole is a result of the heat transfer rate and the mean temperature level in the Borehole water. Therefore in calculations of the thermal resistance in groundwater-filled Boreholes convective heat flow should be included and the actual injection heat transfer rate and mean Borehole temperature should be considered.

  • CFD-modelling of natural convection in a groundwater-filled Borehole heat exchanger
    Applied Thermal Engineering, 2009
    Co-Authors: Anna M.k. Gustafsson, Lars Westerlund, Göran Hellström

    Abstract:

    In design of ground-source energy systems the thermal erformance of the Borehole heat exchangers is important. In Scandinavia, Boreholes are usually not grouted but left with groundwater to fill the space between heat exchanger pipes and Borehole wall. The common U-pipe arrangement in a groundwater-filled BHE has been studied by a three-dimensional, steady-state CFD model. The model consists of a three meter long Borehole containing a single U-pipe with surrounding bedrock. A constant temperature is imposed on the U-pipe wall and the outer bedrock wall is held at a lower constant temperature. The occurring temperature gradient induces a velocity flow in the groundwater-filled Borehole due to density differences. This increases the heat transfer compared to stagnant water. The numerical model agrees well with theoretical studies and laboratory experiments. The result shows that the induced natural convective heat flow significantly decreases the thermal resistance in the Borehole. The density gradient in the Borehole is a result of the heat transfer rate and the mean temperature level in the Borehole water. Therefore in calculations of the thermal resistance in groundwater filled Boreholes convective heat flow should be included and the actual injection heat transfer rate and mean Borehole temperature should be considered.

  • Thermal Response Test – Current Status and World-Wide Application
    Proceedings World Geothermal Congress, 2005
    Co-Authors: Burkhard Sanner, Göran Hellström, Jeff Spitler, Signhild Gehlin

    Abstract:

    To design Borehole heat exchangers (BHE) for Ground Source Heat Pumps (GSHP) or Underground Thermal Energy Storage (UTES), the knowledge of underground thermal properties is paramount. In small plants (residential houses), these parameters usually are estimated. However, for larger plants (commercial GSHP or UTES) the thermal conductivity should be measured on site. A useful tool to do so is a thermal response test, carried out on a BHE in a pilot Borehole (later to be part of the Borehole field). For a thermal response test, basically a defined heat load is put into the hole and the resulting temperature changes of the circulating fluid are measured. Since late 1990s, this technology became more and more popular, and today is used routinely in many countries for the design of larger plants with BHEs, allowing sizing of the Boreholes based upon reliable underground data. The paper includes a short description of the basic concept and the theory behind the thermal response test, looks at the history of its development, and emphasizes on the worldwide experience with this technology.

Lars Westerlund – 2nd expert on this subject based on the ideXlab platform

  • cfd modelling of natural convection in a groundwater filled Borehole heat exchanger
    Applied Thermal Engineering, 2010
    Co-Authors: Annamaria Gustafsson, Lars Westerlund, Göran Hellström

    Abstract:

    In design of ground-source energy systems the thermal performance of the Borehole heat exchangers is important. In Scandinavia, Boreholes are usually not grouted but left with groundwater to fill the space between heat exchanger pipes and Borehole wall. The common U-pipe arrangement in a groundwater-filled BHE has been studied by a three-dimensional, steady-state CFD model. The model consists of a 3 m long Borehole containing a single U-pipe with surrounding bedrock. A constant temperature is imposed on the U-pipe wall and the outer bedrock wall is held at a lower constant temperature. The occurring temperature gradient induces a velocity flow in the groundwater-filled Borehole due to density differences. This increases the heat transfer compared to stagnant water. The numerical model agrees well with theoretical studies and laboratory experiments. The result shows that the induced natural convective heat flow significantly decreases the thermal resistance in the Borehole. The density gradient in the Borehole is a result of the heat transfer rate and the mean temperature level in the Borehole water. Therefore in calculations of the thermal resistance in groundwater-filled Boreholes convective heat flow should be included and the actual injection heat transfer rate and mean Borehole temperature should be considered.

  • CFD-modelling of natural convection in a groundwater-filled Borehole heat exchanger
    Applied Thermal Engineering, 2009
    Co-Authors: Anna M.k. Gustafsson, Lars Westerlund, Göran Hellström

    Abstract:

    In design of ground-source energy systems the thermal erformance of the Borehole heat exchangers is important. In Scandinavia, Boreholes are usually not grouted but left with groundwater to fill the space between heat exchanger pipes and Borehole wall. The common U-pipe arrangement in a groundwater-filled BHE has been studied by a three-dimensional, steady-state CFD model. The model consists of a three meter long Borehole containing a single U-pipe with surrounding bedrock. A constant temperature is imposed on the U-pipe wall and the outer bedrock wall is held at a lower constant temperature. The occurring temperature gradient induces a velocity flow in the groundwater-filled Borehole due to density differences. This increases the heat transfer compared to stagnant water. The numerical model agrees well with theoretical studies and laboratory experiments. The result shows that the induced natural convective heat flow significantly decreases the thermal resistance in the Borehole. The density gradient in the Borehole is a result of the heat transfer rate and the mean temperature level in the Borehole water. Therefore in calculations of the thermal resistance in groundwater filled Boreholes convective heat flow should be included and the actual injection heat transfer rate and mean Borehole temperature should be considered.

Jeffrey D Spitler – 3rd expert on this subject based on the ideXlab platform

  • reference data sets for vertical Borehole ground heat exchanger models and thermal response test analysis
    Geothermics, 2011
    Co-Authors: Richard A. Beier, Marvin D Smith, Jeffrey D Spitler

    Abstract:

    Abstract Ground source heat pump systems often use vertical Boreholes to exchange heat with the ground. Two areas of active research are the development of models to predict the thermal performance of vertical Boreholes and improved procedures for analysis of in situ thermal conductivity tests, commonly known as thermal response tests (TRT). Both the models and analysis procedures ultimately need to be validated by comparing them to actual Borehole data sets. This paper describes reference data sets for researchers to test their Borehole models. The data sets are from a large laboratory “sandbox” containing a Borehole with a U-tube. The tests are made under more controlled conditions than can be obtained in field tests. Thermal response tests on the Borehole include temperature measurements on the Borehole wall and within the surrounding soil, which are not usually available in field tests. The test data provide independent values of soil thermal conductivity and Borehole thermal resistance for verifying Borehole models and TRT analysis procedures. As an illustration, several Borehole models are compared with one of the thermal response tests.