A Perspective Model for Borehole Thermal Resistance Prediction of a Vertical U-Tube in Geothermal Heat Source

Tarrad, Ali H.

doi:10.30958/ajte.7-2-1

Cited by 5 publications

(21 citation statements)

References 8 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The one-dimensional heat transfer process is usually considered for the operation of the ground heat exchangers because the borehole depth is much larger than its diameter. Many correlations are available in the open literature to predict the thermal resistance of the single and double U-tube ground heat exchangers, [16][17][18][19][20][21][22][23][24][25][26][27].…”

Section: Current Approaches In Science and Technology Research Vol 13 A Brief Review And Evaluation Of Available 1-dimensional Models Formentioning

confidence: 99%

“…The correlations of Shonder and Beck [21], Tarrad [25], and Remund [19] predicted the thermal resistance independently of the U-tube spacing. Hence, they produced constant values regardless of the geometry factor for each borehole configuration.…”

Section: Comparison Of the Single Loop Borehole Thermal Resistance Expressions For G2 Configuration At A Variety Of The Geometry Factormentioning

confidence: 99%

“…Tarrad [25] presented a correlation for the borehole thermal resistance based on the equivalent tube diameter technique. He has stated that the equivalent concentric tube has the expression:…”

mentioning

confidence: 99%

“…Tarrad [25] has also emphasized that the shape of the expression in Eq. (5.a) could be utilized for the case when the U-tube composes of different leg sizes which are the usual geometry considered for condensers and evaporators.…”

mentioning

confidence: 99%

See 3 more Smart Citations

A Brief Review and Evaluation of Available 1-Dimensional Models for the Borehole Thermal Performance Prediction in a Ground-Coupled Heat Pump System

Tarrad

2021

Current Approaches in Science and Technology Research Vol. 13

Self Cite

View full text Add to dashboard Cite

The borehole thermal performance prediction is critical in the performance assessment and economical utilization of the ground source heat pump (GSHP). Hence, it is inevitable to evaluate these correlations and reveal their accuracy limits before adapting to the thermal design of the ground heat exchangers. The present article launches an evaluation for the available correlations of the borehole thermal resistance predictions in the direct ground exchange (DX) condenser when it circulates R-410A refrigerant. Eleven elected correlations in the open literature were examined to predict the thermal resistance of vertical single and double U-tube heat exchangers for various geometry configurations. A hypothetical (3.5) kW cooling unit of (3.6) COP was employed to investigate the borehole thermal resistance and depth of the ground copper tubing DX condenser in a single and two-loops design. A large scatter was evident for the borehole thermal resistance and depth as predicted by these correlations. It was as much as double for the examined single and double U-tube geometries. The principal outcome of the present study proved that the utilization of these correlations is only in the preliminary thermal design of the ground source heat pumps (GSHPs). They cannot be adopted for a finalized thermal structure of the borehole without being supported by experimental data due to their predictions' wide range of variations. Many correlations showed good interaction with the borehole configuration, tube diameter (do), tube center-center spacing (Sp), and borehole size (DB). All of the examined models showed that increasing the grout thermal conductivity enhances the thermal performance of the borehole and minimizes the depth for given operating conditions.

show abstract

Section: Current Approaches In Science and Technology Research Vol 13 A Brief Review And Evaluation Of Available 1-dimensional Models Formentioning

confidence: 99%

Section: Comparison Of the Single Loop Borehole Thermal Resistance Expressions For G2 Configuration At A Variety Of The Geometry Factormentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

See 2 more Smart Citations

A Brief Review and Evaluation of Available 1-Dimensional Models for the Borehole Thermal Performance Prediction in a Ground-Coupled Heat Pump System

Tarrad

2021

Current Approaches in Science and Technology Research Vol. 13

Self Cite

View full text Add to dashboard Cite

show abstract

“…Tarrad [17] reported a simple correlation for the prediction of a borehole thermal resistance in a vertical single U-tube ground heat exchanger incorporates the following expression of the equivalent diameter: The correlation showed an acceptable agreement with previously available ones in the open literature. More recently, Tarrad [18] developed a correlation to predict the borehole thermal resistance in which the equivalent tube was derived as:…”

Section: Groutmentioning

confidence: 99%

Development of Analytical Model for a Vertical Single U-Tube Ground-Coupled Heat Pump System

Tarrad¹

2020

GJRE

Self Cite

View full text Add to dashboard Cite

An analytical model was built to study the thermal design of a single vertical U-tube coupled heat pump under steady-state conditions. It was based on the philosophy of U-tube replacement by an equivalent thermal resistance situated between the heat transfer medium that flows inside the tube and the borehole boundary. An obstruction factor was introduced to account for the reduction of heat flow from or to a tube in the borehole due to the presence of the second leg of the U-tube. Two Copper U-tubes with wall factors of (12.5) and (14.29) were implemented to comprise several borehole configurations to verify the present work. The shank spacing was ranged between (2) and (4) times the U-tube outside diameter producing shank spacing to borehole diameter ratio range of (0.29-0.59). The model was utilized for the assessment of DX ground heat exchangers works as a condenser for cooling purposes. Reducing of the tube spacing to tube outside diameter ratio from (3.3) to (2) for both tube wall factors showed a rise for the borehole thermal resistance in the range of (22-54)% and (26.5-28)% predicted at wall factors of (12.5) and (14.29) respectively.

show abstract

Borehole Thermal Analysis for a Closed Loop Vertical U-Tube DX Ground Heat Exchanger

Tarrad¹

2021

MMEP

Self Cite

View full text Add to dashboard Cite

The borehole geometry configuration and its sizing represent great challenges to the thermal equipment designer in the field of geothermal energy source. The present work represents a piece in that direction to avoid elaborate mathematical and computation schemes constraints for the preliminary design of the U-tube ground heat exchanger operates under a steady-state condition. A correlation was built for the prediction of the borehole thermal resistance. The U-tube diameter, leg spacing, borehole diameter, and the offset configuration with respect to the center of the borehole were introduced in the present correlation. An equivalent tube formula and borehole configuration were postulated to possess the same grout volume as the original loop. A variety of geometrical configurations were tested at different U-tube and borehole sizes. The predicted total thermal resistance of the borehole was implemented into the thermal design of the (DX) ground condenser to sizing the borehole U-tube heat exchanger. A hypothetical cooling unit of (1) ton of refrigeration that circulates R410A refrigerant was chosen for the verification of the present model outcomes. The predicted thermal resistance revealed an excellent agreement with other previously published work in this category.

show abstract

A Perspective Model for Borehole Thermal Resistance Prediction of a Vertical U-Tube in Geothermal Heat Source

Cited by 5 publications

References 8 publications

A Brief Review and Evaluation of Available 1-Dimensional Models for the Borehole Thermal Performance Prediction in a Ground-Coupled Heat Pump System

A Brief Review and Evaluation of Available 1-Dimensional Models for the Borehole Thermal Performance Prediction in a Ground-Coupled Heat Pump System

Development of Analytical Model for a Vertical Single U-Tube Ground-Coupled Heat Pump System

Borehole Thermal Analysis for a Closed Loop Vertical U-Tube DX Ground Heat Exchanger

Contact Info

Product

Resources

About