Dimensionless Maps for the Validity of Analytical Ground Heat Transfer Models for GSHP Applications

Conti, Paolo

doi:10.3390/en9110890

Cited by 21 publications

(15 citation statements)

References 24 publications

(38 reference statements)

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“…A reversed semi-log graph has to be used, and Tavg is plotted vs. (tp + Δt)/Δt, as shown by Figure 6c. Effective ground thermal conductivity is then derived from Equation (17) by knowing the log slope m, just like in the case for a standard TRT period. When the temperature recovery line is extended until (tp + Δt)/Δt = 1, initial conditions-i.e., undisturbed ground temperature-are reached.…”

Section: Resultsmentioning

confidence: 99%

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Applying Petroleum the Pressure Buildup Well Test Procedure on Thermal Response Test—A Novel Method for Analyzing Temperature Recovery Period

2018

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Abstract:The theory of Thermal Response Testing (TRT) is a well-known part of the sizing process of the geothermal exchange system. Multiple parameters influence the accuracy of effective ground thermal conductivity measurement; like testing time, variable power, climate interferences, groundwater effect, etc. To improve the accuracy of the TRT, we introduced a procedure to additionally analyze falloff temperature decline after the power test. The method is based on a premise of analogy between TRT and petroleum well testing, since the origin of both procedures lies in the diffusivity equation with solutions for heat conduction or pressure analysis during radial flow. Applying pressure build-up test interpretation techniques to borehole heat exchanger testing, greater accuracy could be achieved since ground conductivity could be obtained from this period. Analysis was conducted on a coaxial exchanger with five different power steps, and with both direct and reverse flow regimes. Each test was set with 96 h of classical TRT, followed by 96 h of temperature decline, making for almost 2000 h of cumulative borehole testing. Results showed that the ground conductivity value could vary by as much as 25%, depending on test time, seasonal period and power fluctuations, while the thermal conductivity obtained from the falloff period provided more stable values, with only a 10% value variation.

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Section: Resultsmentioning

confidence: 99%

“…In thermogeology, the currently most-used method for determining the beginning of semi-steady heat flow is by using the following formula [13,[16][17][18]:…”

Section: Application Of Petroleum Engineering Derivation Curves In Trmentioning

confidence: 99%

Applying Petroleum the Pressure Buildup Well Test Procedure on Thermal Response Test—A Novel Method for Analyzing Temperature Recovery Period

2018

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“…The heat flux transferred between the working fluid and the ground, referred to the length of the pipe, is equal to q l . A dependence, known as the linear source model [22,23], is valid for a single pipe:…”

Section: Mathematical Modelmentioning

confidence: 99%

Study of Ground Heat Exchangers in the Form of Parallel Horizontal Pipes Embedded in the Ground

2018

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Abstract:In order to predict long-term changes in the temperature of the ground in which a horizontal ground heat exchanger has been installed, it is beneficial to implement simplified mathematical models of heat transfer. The possibility of using a one-dimensional equation of heat conduction while modelling heat transfer in a ground heat exchanger with horizontal pipes has been demonstrated in the work. A theoretical analysis based on the linear heat source model as well as experimental research works have been carried out. It has been concluded that the temperature profiles of the ground in which parallel pipes of the heat exchanger are placed do not significantly differ from the profiles for the heat exchanger in the form of a plate; in particular, this refers to large distances from the level in which the pipes are positioned, small distances between pipes axes and the long duration of the process. Discrepancies between the calculated temperature increases for pipe and plate exchangers varied significantly in the individual time intervals, and were approx. 20-30%. The conducted experiments have demonstrated that the temperature field around parallel pipes of the heat exchanger may be described by the linear heat source model. The compatibility of temperature maps that were determined theoretically and experimentally was satisfactory with a good degree of accuracy.

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“…For example, Beier maintained that the calculation method of fluid temperature evolution should be consistent in both the test analysis and the design approach [15]; otherwise, significant errors will be introduced to the design. Although there are relevant studies dealing with the comparison of TRT interpretation models [16][17][18], few have concentrated on the influence of TRTPE models on the BHE system design. Are the heat transfer model used in TRT data interpretation and the underlying model in the design calculation based on a consistent assumption?…”

Section: Introductionmentioning

confidence: 99%

Comparison of Four Methods for Borehole Heat Exchanger Sizing Subject to Thermal Response Test Parameter Estimation

Zhang

et al. 2019

Energies

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The impact of different parameter estimation results on the design length of a borehole heat exchanger has received very little attention. This paper provides an in-depth investigation of this problem, together with a full presentation of six data interpretation models and a comprehensive comparison of four representative sizing methods and their inter models. Six heat transfer models were employed to interpret the same thermal response test data set. It was found that the estimated parameters varied with the data interpretation model. The relative difference in borehole thermal resistance reached 34.4%, and this value was 11.9% for soil thermal conductivity. The resulting parameter estimation results were used to simulate mean fluid temperature for a single borehole and then to determine the borehole length for a large bore field. The variations in these two correlated parameters caused about 15% and 5% relative difference in mean fluid temperature in the beginning and at the end of the simulation period, respectively. For computing the borehole design length, software-based methods were more sensitive to the influence of parameter estimation results than simple equation-based methods. It is expected that these comparisons will be beneficial to anyone involved in the design of ground-coupled heat pump systems.

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Dimensionless Maps for the Validity of Analytical Ground Heat Transfer Models for GSHP Applications

Cited by 21 publications

References 24 publications

Applying Petroleum the Pressure Buildup Well Test Procedure on Thermal Response Test—A Novel Method for Analyzing Temperature Recovery Period

Applying Petroleum the Pressure Buildup Well Test Procedure on Thermal Response Test—A Novel Method for Analyzing Temperature Recovery Period

Study of Ground Heat Exchangers in the Form of Parallel Horizontal Pipes Embedded in the Ground

Comparison of Four Methods for Borehole Heat Exchanger Sizing Subject to Thermal Response Test Parameter Estimation

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