BHE Dataset Editor
BHE Datasets define prototype type, geometry and calculation method configurations of Borehole Heat Exchangers (BHE). they are used for the definition of BHE in the model. A toolbar provides options to manage the datasets:
| Symbol | Description |
|---|---|
 |
Add new borehole heat exchanger dataset. |
 |
Delete current borehole heat exchanger dataset. |
 |
Load borehole heat exchanger dataset file (s). |
 |
Save current borehole heat exchanger dataset. |
 |
Save all borehole heat exchanger datasets. |
The
Save and
Load options can be used to transfer
borehole heat exchanger datasets between different models. the *.xml
format is used for this purpose. The actual properties of the BHE prototype
described in the following are edited in the table in the center of the
dialog.
Geometry
Four different Geometries of BHE are supported:
The geometric parameters depend on the geometry of BHE, and their respective meaning is explained in the graphics in the lower part of the dialog. the drawing reflects the currently set properties, so that geometrical mismatches can be easily detected.
Single or Double U-shape
| Parameter | Unit | Default |
|---|---|---|
| Borehole Diameter (D) | [L] | 0.15 m |
| Pipe Distance (w) | [L] | 0.04 m |
| Inlet Pipe Diameter (d-in) | [L] | 0.032 m |
| Inlet Pipe Wall thickness (b-in) | [L] | 0.0029 m |
| Outlet Pipe Diameter (d-out) | [L] | 0.032 m |
| Outlet Pipe Wall thickness (b-out) | [L] | 0.0029 m |
Coaxial (annular inlet)
| Parameter | Unit | Default |
|---|---|---|
| Borehole Diameter (D) | [L] |
0.15 m |
| Inlet Pipe Diameter (d-in) | [L] | 0.06 m |
| Inlet Pipe Wall thickness (b-in) | [L] | 0.0029 m |
| Outlet Pipe Diameter (d-out) | [L] | 0.032 m |
| Outlet Pipe Wall thickness (b-out) | [L] | 0.0029 m |
Coaxial (centered inlet)
| Parameter | Unit | Default |
|---|---|---|
| Borehole Diameter (D) | [L] |
0.15 m |
| Inlet Pipe Diameter (d-in) | [L] | 0.032 m |
| Inlet Pipe Wall thickness (b-in) | [L] | 0.0029 m |
| Outlet Pipe Diameter (d-out) | [L] | 0.06 m |
| Outlet Pipe Wall thickness (b-out) | [L] | 0.0029 m |
Computational method
The fully transient (Al-Khoury et al.) method provides higher accuracy for short-term predictions in time ranges smaller than hours, especially in conditions with quickly changing inflow temperature.
In case of more long-term simulations with less frequent and less steep inflow temperature changes the quasi-stationary (Eskilson & Claesson) method provides a reasonable accuracy at lower computational cost. the analytical solution assumes a local thermal equilibrium between all the elements of the BHE (pipes, grout, ground) at any time of the simulation.
Heat-transfer coefficients the heat transfer coefficients used for the analytical or numerical simulation of the heat transfer between the elements of the borehole heat exchanger and the ground can be input in three different ways:
Computed
With this option, the heat-transfer coefficients are calculated from the geometrical information and the thermal conductivities of the different BHE parts:
| Parameter | Unit | Default |
|---|---|---|
| Inlet-pipe thermal conductivity (tc-in) | [E/L/S/K] |
0 J/m/s/K |
| Inlet-pipe thermal conductivity (tc-out) | [E/L/S/K] | 0 J/m/s/K |
| Grout thermal conductivity (tc-grout) | [E/L/S/K] | 0 J/m/s/K |
The computed heat-transfer coefficients are shown in the parameter list, but without the possibility to change them directly.
Hellstroem
With this option, the heat-transfer coefficients are calculated from thermal resistances that are typically derived from thermal response testing:
| Parameter | Unit | Default |
|---|---|---|
| Borehole thermal resistance (Rb) | [L*T*θ/E] |
0.08 msK/J |
| Internal borehole thermal resistance (Ra) | [L*T*θ/E] | 0.3 msK/J |
The computed heat-transfer coefficients are shown in the parameter list, but without the possibility to change them directly.
|
|
White Paper Vol. V, Chapter 1.7. |
User-defined
With this option, the heat-transfer coefficients can be input directly:
| Parameter | Unit | Default |
|---|---|---|
| Grout volumetric heat capacity (numerical method only) | [E/m³/K] | 2.5*106 J/m³/K |
| Pipes-in to grout | [L*T*θ/E] |
1.608*10-8 msK/J |
| Pipes-out to grout | [L*T*θ/E] | 1.608*10-8 msK/J |
| Grout to grout (1) | [L*T*θ/E] | 1.34*10-5 msK/J |
| Grout to grout (2) | [L*T*θ/E] | 1.34*10-5 msK/J |
| Grout to soil | [L*T*θ/E] | 2.679*10-9 msK/J |
Refrigerant Properties
| Parameter | Unit | Default |
|---|---|---|
| Refrigerant volumetric heat capacity | [E/L³/θ] |
4*106 J/m³/K |
| Refrigerant thermal conductivity | [E/L/T/θ] | 0.48 J/m/s/K |
| Refrigerant dynamic viscosity | [M/L/T] | 0.52*10-3 kg/m/s |
| Refrigerant density | [M/L³] | 1.052*10³ kg/m³ |