modelHexInternalElement

Internal part of a borehole

Extends from Buildings.Fluid.Interfaces.FourPortHeatMassExchanger.

Information

Model for the heat transfer between the fluid and within the borehole filling. This model computes the dynamic response of the fluid in the tubes, the heat transfer between the fluid and the borehole filling, and the heat storage within the fluid and the borehole filling.

This model computes the different thermal resistances present in a single-U-tube borehole using the method of Bauer et al. (2011) and computing explicitly the fluid-to-ground thermal resistance R_b and the grout-to-grout resistance R_a as defined by Hellstroem (1991) using the multipole method. The multipole method is implemented in Buildings.Fluid.Geothermal.Boreholes.BaseClasses.singleUTubeResistances. The convection resistance is calculated using the Dittus-Boelter correlation as implemented in Buildings.Fluid.Geothermal.Boreholes.BaseClasses.convectionResistance.

The figure below shows the thermal network set up by Bauer et al. (2010).

References

G. Hellström. Ground heat storage: thermal analyses of duct storage systems (Theory). Dept. of Mathematical Physics, University of Lund, Sweden, 1991.

D. Bauer, W. Heidemann, H. Müller-Steinhagen, and H.-J. G. Diersch. Thermal resistance and capacity models for borehole heat exchangers . International Journal Of Energy Research, 35:312–320, 2011.

Parameters

Type	Name	Default	Description
Modelica.Units.SI.ThermalConductivity	kSoi		Thermal conductivity of the soil used for the calculation of the internal interference resistance
Modelica.Units.SI.Height	hSeg		Height of the element
Modelica.Units.SI.Radius	rBor		Radius of the borehole
Modelica.Units.SI.Length	xC	0.05	Shank spacing, defined as half the center-to-center distance between the two pipes
Filling material
Buildings.HeatTransfer.Data.BoreholeFillings.Generic	matFil		Thermal properties of the filling material
Modelica.Units.SI.Temperature	TFil_start	283.15	Initial temperature of the filling material
Soil
Buildings.HeatTransfer.Data.Soil.Generic	matSoi		Thermal properties of soil
Pipes
Modelica.Units.SI.Radius	rTub	0.02	Radius of the tubes
Modelica.Units.SI.ThermalConductivity	kTub	0.5	Thermal conductivity of the tubes
Modelica.Units.SI.Length	eTub	0.002	Thickness of the tubes

Components

Type	Name	Description
Modelica.Thermal.HeatTransfer.Interfaces.HeatPort_a	port	Heat port that connects to filling material
Modelica.Thermal.HeatTransfer.Components.HeatCapacitor	capFil1	Heat capacity of the filling material
Modelica.Thermal.HeatTransfer.Components.HeatCapacitor	capFil2	Heat capacity of the filling material

Name	Description
Medium	Medium in the component

Revisions

May 6, 2015, by Michael Wetter:
Removed assignement of vol.allowFlowReversal as this is done in the base class.
June 18, 2014, by Michael Wetter:
Added initialization for temperatures and derivatives of capFil1 and capFil2 to avoid a warning during translation.
February 14, 2014, by Michael Wetter:
Removed unused parameters B0 and B1.
January 24, 2014, by Michael Wetter:
Revised implementation, added comments, replaced HeatTransfer.Windows.BaseClasses.ThermalConductor with resistance models from the Modelica Standard Library.
January 23, 2014, by Damien Picard:
First implementation.