Buildings.Fluid.FixedResistances.BuriedPipes

Package with models for buried pipes

Information

This package contains models for buried pipes, such as those found in district heating and cooling distribution networks.

Extends from Modelica.Icons.VariantsPackage (Icon for package containing variants).

Package Content

Name	Description
GroundCoupling	Thermal coupling between buried pipes and ground
PipeGroundCoupling
Examples	Collection of models that illustrate model use and test models
Validation	Collection of validation models
BaseClasses	Package with base classes for Buildings.Fluid.Geothermal.BuriedPipes

Buildings.Fluid.FixedResistances.BuriedPipes.GroundCoupling

Thermal coupling between buried pipes and ground

Information

This model simulates the heat transfer between multiple buried pipes and the ground, using climate and soil information and the geometry of the pipes network.

The model can take any number of pipes, and can be discretized axially in any number of segments. Currently, the model only allows for pipes that run co-axially and parallel to the ground, and the axial segmentation must be the same for each pipe.

The heat transfer solution is based upon the potential flow theory and obtained by the use of "mirror-image" technique suggested by Eckert (1959). This technique is extended to a network with multiple pipes by Kusuda (1981) in the equation:

where:
L = pipe length [m]
k_s = soil thermal conductivity [W/(m.K)]
P_ij = geometric factor (see Buildings.Fluid.FixedResistances.BuriedPipes.BaseClasses.groundCouplingFactors for more information)
Q_i = net heat transfer from pipe i [W]
T_i = temperature at the exterior surface of pipe i [degC]
T_g = undisturbed ground temperature at the depth of the network. [degC]

This model relies on the following assumptions.

• Heat transfer is in steady state.
• The heat transfer is radial (no axial diffusion).
• The exterior surfaces for each pipe segment are isothermic planes.
• The ground surface is an isothermic plane.
• The soil conductivity is homogeneous and isotropic.

References

Eckert, E. R. G. (1959). Heat and Mass Transfer. McGraw-Hill Book Company.
Kusuda, T. (1981). Heat transfer analysis of underground heat and chilled-water distribution systems. National Bureau of Standards.

Parameters

Connectors

Modelica definition

Buildings.Fluid.FixedResistances.BuriedPipes.PipeGroundCoupling

Information

This model considers the conduction heat transfer between the buried pipe wall and the undisturbed ground temperature by adding a dynamic ground layer. The dynamic ground layer is modeled using the radial heat conduction model through a hollow cylinder Buildings.HeatTransfer.Conduction.SingleLayerCylinder. The undisturbed ground temperature is calculated by the model Buildings.BoundaryConditions.GroundTemperature.UndisturbedSoilTemperature. This model can consider an axial discretization of the pipe. A figure highlighting the main variables and parameters is shown below:

References

Ettore Zanetti, David Blum, Michael Wetter (2023) Control development and sizing analysis for a 5th generation district heating and cooling network using Modelica, In Proceedings of the 15th International Modelica Conference. Aachen, Germany, Oct 9-11, 2023.

Parameters

Connectors

Modelica definition