BHE Editor

This dialog provides the means to define and edit the properties of Borehole Heat Exchangers. In can be opened via a double-click on the Borehole heat exchanger entry in the input box of the Editor toolbar.

For the entire workflow of input and editing of borehole heat exchangers, please refer to the related workflow page.

The inflow boundary of a borehole heat exchanger is defined by a Flow Rate and information about the inflow temperature. The latter can be defined in four different ways:

 

Parameter	Description	Unit	Default
Inlet Temperature	Defined temperature of inflow	[Θ]	0 °C
Heat Input Rate	Defined difference in energy per time with respect to refrigerant at Reference Temperature	[E/T]	0 J/d
Temperature Difference	Temperature difference between inlet and outlet of the BHE, i.e. positive values correspond to a heating of the refrigerant	[Θ]	0 K / 0 °C
Power	Difference in thermal energy per time between inlet and outlet of the BHE, i.e. positive values correspond to a heating of the refrigerant	[E/T]	0 MJ/d
Energy	Energy E in kilowatt-hours (kWh) equals Power P in kilowatts (kW) times period of usage. Please, be aware that FEFLOW default time unit for usage in BHE Editor is days. The user will have to convert hours to days, when necessary.	[E]	0 MJ

 

The application of differences is based on the outlet temperature of the last calculated time step (non-iterative). In case of very dynamic changes it is recommended to choose short time steps, if necessary by limiting the time step size.

 

The parameter Heat Input Rate is no longer used in the current FEFLOW, it only exists in older versions of FEFLOW. For backward compatibility reasons, we have kept this parameter so that it is not lost when you open very old FEFLOW models.

 

The parameter Energy can be defined by means of Time Series. In this case, each Value in the Time Series should be equal to the Power expected multiplied times the correspondent timestep length of the Time Series. For example: Energy daily values in [KWh] should be equal to Power [kW] * 24 [h]

 

Both Flow Rate and the respective parameter defining the inflow temperature can be set either constant in time or time-varying. The input mode for these two options can be switched by left- or right click on the icon in the input box. In case of temporally varying properties the Time Series to be used have to be defined in advance to be available in the input box.

Vertical Extent

The extent of the borehole heat exchanger along the z axis (typically vertical) is defined here. Three options are available:

 

Vertical Extend	Description
From Selected Join Edges	Defines the extent of the Multilayer well according to the selected edges.
From Top and Bottom Elevation	Top and Bottom of BHE can be set and refer to the elevation of the screen.
From Depth to Top and Bottom	Depth to Top or Bottom of BHE define the position of the borehole heat exchanger related to the elevation of slice 1, which usually refers to the ground surface.

 

Borehole heat exchangers always extend across entire layers. If top or bottom of the well screen are defined within a layer, the layer is included if more than half of the layer thickness is penetrated by the BHE. As a means of quick checking the sketch on the right of the dialog shows the defined screen in black and the resulting BHE top, bottom and covered slices in between via boundary condition symbols.

BHE Dataset

BHE Datasets define prototype type, geometry and calculation method configurations for BHE. Using the combo-box an existing dataset can be chosen to be used for the BHE to be defined. The properties of the chosen dataset are shown in the table on the bottom, and the BHE geometry defined in the dataset is shown as a cross-section through the BHE on the lower right of the dialog.

The Edit borehole heat exchanger datasets button on the right of the combo box can be pressed to edit existing datasets or define new datasets in the BHE Dataset Editor.

Location Selection

In case that Edges at different X-Y locations are selected, the arrow buttons can be used to switch between the different locations. Thus BHE at different locations can be defined or edited without having to close the BHE Editor and open it again for each single location.

BHE Coordinates are shown to identify the current location.