An improved thermal response test for U-tube ground heat exchanger based on optical fiber thermometers

Fujii, Hikari; Okubo, Hiroaki; Nishi, Keita; Itoi, Ryuichi; Ohyama, Kunio; Shibata, Kazuo

doi:10.1016/j.geothermics.2009.06.002

Cited by 184 publications

(80 citation statements)

References 5 publications

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“…Such configuration enables distributed temperature measurements along the depth of the borehole. In other studies authors used fiber optic cables placed inside the U-pipe [13], based on works of Acuna [2] and Fujii [14].…”

Section: Experimental Rigmentioning

confidence: 99%

Ground Thermal Response and Recovery after Heat Injection: Experimental Investigation

Boban

Soldo

Stošić

et al. 2018

TFAMENA

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SummaryMonitoring the ground thermal response to a constant heat flux input is common method for determination of effective ground properties needed for sizing the ground coupled heat pumps. In this work, the experimental procedure included two TRT's with different average injection heat fluxes, 4.43 kW and 7.64 kW, applied to the same borehole. Recorded temperatures of fluids, circulated in an experimental borehole heat exchanger U-tube, are used to determine the ground thermal conductivity and the borehole thermal resistance with the infinite line source model (ILS). Additionally, thermocouples placed on the borehole wall up to the depth of 100 m enabled the measurement of temperature profiles of undisturbed ground and during the recovery period between the two TRTs. The results indicate that true undisturbed state after injected heat flux cannot be reached in short time while the use of higher injection heat flux reduces the influence of the ground's inhomogeneity on the results obtained.

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Section: Experimental Rigmentioning

confidence: 99%

Ground Thermal Response and Recovery after Heat Injection: Experimental Investigation

Boban

Soldo

Stošić

et al. 2018

TFAMENA

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“…Measurements of such temperature profile during TRTs were performed by Fujii et al [16] and Acuña et al [17] using fiber optic sensors. Unfortunately, the apparatus to evaluate temperature with optical fiber is expensive.…”

Section: Temperature Measurement At the Bottom Of The Ghementioning

confidence: 99%

“…From these thermal resistance results (Table 3), the expected normalized temperature profile given by Equations (16) and (17) is compared with the measured temperature values ( Figure 7). As noted previously, normalized fluid temperatures are time dependent and the absolute temperatures are given for a specific time.…”

Section: Beier Profilementioning

confidence: 99%

“…One of the advantages of the Beier's profile is that it is not based on a vertically uniform borehole temperature, an assumption that has been the subject of debates [7,8]. However, one of the disadvantages is that the normalized temperature profile found with Equations (16) and (17) is not time independent, even in the steady-flux regime. The short-circuiting effect in the delta equivalent circuit between both legs of the U-tube will follow two possible paths, a direct one through R 12 and an indirect one via the borehole wall temperature T b (Figure 2).…”

Section: Beier Profilementioning

confidence: 99%

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Evaluation of the Internal and Borehole Resistances during Thermal Response Tests and Impact on Ground Heat Exchanger Design

2017

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Abstract:The main parameters evaluated with a conventional thermal response test (TRT) are the subsurface thermal conductivity surrounding the borehole and the effective borehole thermal resistance, when averaging the inlet and outlet temperature of a ground heat exchanger with the arithmetic mean. This effective resistance depends on two resistances: the 2D borehole resistance (R b ) and the 2D internal resistance (R a ) which is associated to the short-circuit effect between pipes in the borehole. This paper presents a field method to evaluate these two components separately. Two approaches are proposed. In the first case, the temperature at the bottom of the borehole is measured at the same time as the inlet and outlet temperatures as done in a conventional TRT. In the second case, different flow rates are used during the experiment to infer the internal resistance. Both approaches assumed a predefined temperature profile inside the borehole. The methods were applied to real experimental tests and compared with numerical simulations. Interesting results were found by comparison with theoretical resistances calculated with the multipole method. The motivation for this work is evidenced by analyzing the impact of the internal resistance on a typical geothermal system design. It is shown to be important to know both resistance components to predict the variation of the effective resistance when the flow rate and the height of the boreholes are changed during the design process.

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“…An optical fiber is unrolled in the underground and it is then possible to obtain an average temperature value at each meter of optical fiber. This technology of temperature measurement has been already used for geothermal energy studies to measure the temperature evolution around borehole heat exchangers by Fujii (Fujii, 2009). …”

Section: Temperature Measurement In the Undergroundmentioning

confidence: 99%

Horizontal Ground Heat Exchangers

Chiasson¹

2016

Geothermal Heat Pump and Heat Engine Systems

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This study aims to present a comparison between temperature measurements relative to horizontal ground heat exchangers with predicted values using thermal response test. A scale 1 test facility of horizontal ground heat exchangers has been implemented in BRGM (Orleans -France) to test performances in real conditions. The heat exchanger is divided in four parts of 100 m² each with different characteristics:a sunny grass -a shaded grass -a sunny car-park -a shaded car-park These different configurations have been chosen to compare the performances of ground heat exchangers in different environments (surface state, boundary conditions). Furthermore, the temperature in the soil is measured continuously at 3 different levels (-0.5 m, -1 m, -1.5 m). To cartography the temperature field at these 3 depths, optical fibers are distributed in the underground and the use of a distributed temperature sensor (DTS) allows to accurately measure the temperature in the soil surrounding the ground heat exchanger.A thermal response is carried out on the horizontal ground heat exchanger. A monitored constant heating power is injected at a constant mass flow. The temperature measurements at the 3 different levels of a threedimensional numerical model of ground heat exchanger.The thermal response test gives in particular the noticeable differences between the 4 different conditions of each part of the ground heat exchanger. The conclusion will give indications on the consequences of uncertainty about soil thermal properties on sizing.

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An improved thermal response test for U-tube ground heat exchanger based on optical fiber thermometers

Cited by 184 publications

References 5 publications

Ground Thermal Response and Recovery after Heat Injection: Experimental Investigation

Ground Thermal Response and Recovery after Heat Injection: Experimental Investigation

Evaluation of the Internal and Borehole Resistances during Thermal Response Tests and Impact on Ground Heat Exchanger Design

Horizontal Ground Heat Exchangers

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