Validation of borehole heat exchanger models against multi-flow rate thermal response tests

Beier, Richard A.; Mitchell, Matt S.; Spitler, Jeffrey D.; Javed, Saqib

doi:10.1016/j.geothermics.2017.08.006

Cited by 16 publications

(13 citation statements)

References 19 publications

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“…A comparison of experimental measurements presented by Beier et al (2018) to a conventional borehole model using the simple mean fluid temperature approximation gives quite good results over a wide range of flow rates as long as the thermal short-circuiting is accounted for. That is, to obtain good accuracy, the effective borehole thermal resistance ( * ) should be used as shown in Figure 14 of Beier et al (2018) rather than the local borehole thermal resistance ( ). When the local borehole thermal resistance is used with the simple mean fluid temperature approximation (labeled "1D model with f = 0.5"" in Figures 9 and 11 of Beier et al (2018)) errors exceed 1°C at Reynolds numbers below about 6,500.…”

mentioning

confidence: 92%

“…(3.6) Equation 3.5 assumes that the simple mean fluid temperature is an adequate approximation to the true mean fluid temperature. More sophisticated models are available (Rees 2015, Beier et al 2018, but this sophistication is mainly important at short times, below an hour, when transit time effects are predominant. A comparison of experimental measurements presented by Beier et al (2018) to a conventional borehole model using the simple mean fluid temperature approximation gives quite good results over a wide range of flow rates as long as the thermal short-circuiting is accounted for.…”

mentioning

confidence: 99%

“…More sophisticated models are available (Rees 2015, Beier et al 2018, but this sophistication is mainly important at short times, below an hour, when transit time effects are predominant. A comparison of experimental measurements presented by Beier et al (2018) to a conventional borehole model using the simple mean fluid temperature approximation gives quite good results over a wide range of flow rates as long as the thermal short-circuiting is accounted for. That is, to obtain good accuracy, the effective borehole thermal resistance ( * ) should be used as shown in Figure 14 of Beier et al (2018) rather than the local borehole thermal resistance ( ).…”

mentioning

confidence: 99%

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confidence: 99%

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“…Various studies have focused on a better understanding and more precise estimation of effective thermal conductivity and borehole thermal resistance [1][2][3][4] as important parameters when exploiting the shallow geothermal resource. Current methods of determining the average fluid temperature within BHE, as well as the influence of various measuring methods during TRT, on the final determination of thermal properties are also available [5][6][7]. With newly established data interpretation of time derivative of fluid temperature, measured during the first few hours of TRT operation, it was shown that the duration of the test could be shortened significantly, while the values of effective thermal conductivity can still be estimated within the 10% margin of error [8].…”

Section: Introduction and Literature Overviewmentioning

confidence: 99%

Investigation of Steady-State Heat Extraction Rates for Different Borehole Heat Exchanger Configurations from the Aspect of Implementation of New TurboCollector™ Pipe System Design

et al. 2019

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When considering implementation of shallow geothermal energy as a renewable source for heating and cooling of buildings, special care should be taken in the hydraulic design of the borehole heat exchanger system. Laminar flow can occur in pipes due to the usage of glycol mixtures at low temperature or inadequate flow rates. This can lead to lower heat extraction and rejection rates of the exchanger because of higher thermal resistance. Furthermore, by increasing the flow rate to achieve turbulent flow and satisfactory heat transfer rate can lead to an increase in the pressure drop of the system and oversizing of the circulation pump which leads to impairment of the seasonal coefficient of performance at the heat pump. The most frequently used borehole heat exchanger system in Europe is a double-loop pipe system with a smooth inner wall. Lately, development is focused on the implementation of a different configuration as well as with ribbed inner walls which ensures turbulent flow in the system, even at lower flow rates. At a location in Zagreb, standard and extended thermal response tests were conducted on three different heat exchanger configurations in the same geological environment. With a standard TRT test, thermogeological properties of the ground and thermal resistance of the borehole were determined for each smooth or turbulator pipe configuration. On the other hand, extended Steady-State Thermal Response Step Test (TRST) incorporates a series of power steps to determine borehole extraction rates at the defined steady-state heat transfer conditions of 0/–3 °C. When comparing most common exchanger, 2U-loop D32 smooth pipe, with novel 1U-loop D45 ribbed pipe, an increase in heat extraction of 6.5% can be observed. Also, when the same comparison is made with novel 2U-loop D32 ribbed pipe, an increase of 18.7% is achieved. Overall results show that heat exchangers with ribbed inner pipe wall have advantages over classic double-loop smooth pipe designs, in terms of greater steady-state heat extraction rate and more favorable hydraulic conditions.

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“…Beier et al [7] studied a borehole heat transfer model that uses a transient weighting factor to calculate the average circulating fluid temperature along the borehole has been applied to analyse multi-flow rate thermal response tests (MFR-TRT) The model accounts for short-circuiting by an analytically computed weighting factor that is used to determine the mean fluid temperature. It was stated that both; the effective borehole thermal resistance model and the weighting factor give quite good results a few hours after a step change in flow rate, the weighting factor model gives much better results in the first few hours after a step change in flow rate.…”

Section: Introduction and Literature Overviewmentioning

confidence: 99%

Investigation of Steady-State Heat Extraction Rates for Different Borehole Heat Exchanger Configuration from the Aspect of Implementation of New TurboCollectorTM Pipe System Design

Kurevija¹,

Mehrjerdi²,

Macenić³

et al. 2019

Preprint

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When considering implementation of shallow geothermal energy as a renewable source for heating and cooling of the building, special care should be taken in hydraulic design of borehole heat exchanger system. Laminar flow can occur in pipes due to usage of glycol mixture at low temperature or inadequate flow rate. This can lead to lower heat extraction and rejection rates of the exchanger because of higher thermal resistances. Furthermore, by increasing flow rate to achieve turbulent flow and satisfactory heat transfer rate can lead to increase the pressure drop of the system and oversizing of circulation pump which leads to impairment of seasonal coefficient of performance at the heat pump. Most frequently used borehole heat exchanger system in Europe is double-loop pipe system with smooth inner wall. Lately, development is focused on implementation of different configuration as well as with ribbed inner wall which ensures turbulent flow in the system, even at lower flow rates. At a location in Zagreb, classical and extended thermal response test was conducted on three different heat exchanger configurations in the same geological environment. With classic TRT test, thermogeological properties of the ground and thermal resistance of the borehole were determined for each smooth or turbulator pipe configuration. Extended Steady-State Thermal Response Step Test (TRST) was implemented, which incorporate series of power steps to determine borehole extraction rate at the define steady-state heat transfer conditions of 0/-3°C. Results show that heat exchangers with ribbed inner pipe wall have advantages over classic double-loop smooth pipe design, in terms of greater steady state heat extraction rate and more favorable hydraulic conditions.

show abstract

Validation of borehole heat exchanger models against multi-flow rate thermal response tests

Cited by 16 publications

References 19 publications

FY20 Third Milestone Report for Advanced Techno-Economic Modeling for Geothermal Heat Pump Applications in Residential, Commercial, and Industry Buildings

FY20 Third Milestone Report for Advanced Techno-Economic Modeling for Geothermal Heat Pump Applications in Residential, Commercial, and Industry Buildings

Investigation of Steady-State Heat Extraction Rates for Different Borehole Heat Exchanger Configurations from the Aspect of Implementation of New TurboCollector™ Pipe System Design

Investigation of Steady-State Heat Extraction Rates for Different Borehole Heat Exchanger Configuration from the Aspect of Implementation of New TurboCollectorTM Pipe System Design

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