| 1. |
- Claesson, Johan, 1943, et al.
(författare)
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A load-aggregation method to calculate extraction temperatures of borehole heat exchangers
- 2012
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Ingår i: ASHRAE Transactions. - 0001-2505. ; 118:1, s. 530-539
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Konferensbidrag (refereegranskat)abstract
- Hourly simulations of extraction fluid temperatures from borehole heat exchangers tend to be very time consuming. A new load aggregation scheme to perform long-term simulations of borehole heat exchangers is presented. The starting point is the step-response function for the considered borehole heat exchanger and the corresponding long sequence of cells, each with a load and a weighting factor. On the first level, the original weighting factors are kept. On the following levels, 2, 4, 8, etc., the weighting factors are lumped together. The lumped weighting factors are obtained directly from the step-response function. The number of cells to be lumped together is chosen so that the extraction temperatures using lumped weighting factors give a sufficiently good approximation of the non-aggregated scheme. The new scheme is applied to a test case to simulate extraction fluid temperature over a 20-year time period. Comparison of the results from the new scheme with the non-aggregated setting shows that the new scheme can perform very accurate and fast simulations of borehole heat exchangers.
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| 2. |
- Javed, Saqib, 1978, et al.
(författare)
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A method to evaluate thermal response tests on groundwater-filled boreholes
- 2012
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Ingår i: ASHRAE Transactions. - 0001-2505. ; 118:1, s. 540-549
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Konferensbidrag (refereegranskat)abstract
- The design of borehole heat exchangers for ground source heat pump system applications requires thermal properties, like ground thermal conductivity and borehole thermal resistance, as inputs. These properties are often determined from an in-situ thermal response test of a pilot borehole. For groundwater-filled boreholes, the ground thermal conductivity and borehole resistance estimations are affected by the heat-injection rates used during the test. Most existing methods for evaluating thermal response tests were not originally developed to analyze tests on groundwater-filled boreholes, and these methods can sometimes give erroneous results in such situations. This paper presents a new method for the evaluation of thermal response tests on grouted and groundwater-filled boreholes. The method is based on an analytical solution, which considers the thermal capacities, thermal resistances, and thermal properties of all borehole elements. The proposed method simplifies the evaluation of thermal response tests on groundwater-filled boreholes and provides accurate estimations of ground thermal conductivity and borehole thermal resistance.
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| 3. |
- Javed, Saqib, 1978, et al.
(författare)
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Second-order Multipole Formulas for Thermal Resistance of Single U-tube Borehole Heat Exchangers
- 2017
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Ingår i: Proceedings of the IGSHPA Technical/Research Conference and Expo 2017, March 14-16, Denver. - : International Ground Source Heat Pump Association.
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Konferensbidrag (refereegranskat)abstract
- The borehole thermal resistance is both an important design parameter and a key performance characteristic of a borehole heat exchanger. Another quantity that is particularly important for deep borehole heat exchangers is the internal thermal resistance between the upward-flowing and downward-flowing fluid channels in the borehole. The multipole method is a well-known and robust method to compute both these thermal resistances. However, it has a fairly intricate mathematical algorithm and is thus not trivial to implement. Consequently, there is considerable interest in developing explicit multipole formulas. So far zeroth-order and first-order multipole formulas have been derived for cases where the two legs of the borehole are placed symmetrically in a borehole. This paper presents new explicit second-order multipole formulas, which provide significant accuracy improvements over the previous formulas.
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