modelTwoUTubes
Borefield model containing double U-tube boreholes
Extends from Buildings.Fluid.Geothermal.ZonedBorefields.BaseClasses.PartialStorage (Partial model for borehole thermal energy storage with independent borefield zones).
Information
This model simulates a borehole thermal energy storage system with multiple
zones of double U-tube boreholes. Boreholes within the same zone are connected
in parallel. The borefield configuration and thermal parameters are defined in
the borFieDat record.
Heat transfer to the soil is modeled using only one borehole heat exchanger per zone. The fluid mass flow rate into each borehole is divided to reflect the per-borehole fluid mass flow rate. The borehole model calculates the dynamics within the borehole itself using an axial discretization and a resistance-capacitance network for the internal thermal resistances between the individual pipes and between each pipe and the borehole wall.
The ground thermal response at each borehole segment is evaluated using analytical thermal response factors. Spatial and temporal superposition are used to evaluate the total temperature change at each of the borehole segments.
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| Integer | nPorts (from PartialTwoNPorts) | Number of fluid ports on each side | |
| Modelica.Units.SI.Time | tLoaAgg (from PartialStorage) | 3600.0 | Time resolution of load aggregation |
| Integer | nCel (from PartialStorage) | 5 | Number of cells per aggregation level |
| Integer | nSeg (from PartialStorage) | 10 | Number of segments to use in vertical discretization of the boreholes |
| Buildings.Fluid.Geothermal.ZonedBorefields.Data.Borefield.Template | borFieDat (from PartialStorage) | Borefield data record | |
| Integer | nZon (from PartialStorage) | borFieDat.conDat.nZon | Total number of independent bore field zones |
| Integer | nBorPerZon (from PartialStorage) | borFieDat.conDat.nBorPerZon | Number of boreholes per borefield zone |
| Assumptions | |||
| Boolean | allowFlowReversal (from PartialTwoNPorts) | true | = false to simplify equations, assuming, but not enforcing, no flow reversal |
| Nominal condition | |||
| Modelica.Units.SI.MassFlowRate[nPorts] | m_flow_nominal (from PartialTwoNPortsInterface) | Nominal mass flow rate | |
| Modelica.Units.SI.PressureDifference[nPorts] | dp_nominal (from TwoNPortsFlowResistanceParameters) | Pressure difference | |
| Advanced | |||
| Modelica.Units.SI.MassFlowRate[nPorts] | m_flow_small (from PartialTwoNPortsInterface) | 1E-4*abs(m_flow_nominal) | Small mass flow rate for regularization of zero flow |
| Advanced › Diagnostics | |||
| Boolean | show_T (from PartialTwoNPortsInterface) | false | = true, if actual temperature at port is computed |
| Flow resistance | |||
| Boolean[nPorts] | computeFlowResistance (from TwoNPortsFlowResistanceParameters) | fill(true, nPorts) | =true, compute flow resistance. Set to false to assume no friction |
| Boolean[nPorts] | from_dp (from TwoNPortsFlowResistanceParameters) | fill(false, nPorts) | = true, use m_flow = f(dp) else dp = f(m_flow) |
| Real | n (from TwoNPortsFlowResistanceParameters) | 2 | Flow exponent, n=1 for laminar, n=2 for turbulent |
| Boolean[nPorts] | linearizeFlowResistance (from TwoNPortsFlowResistanceParameters) | fill(false, nPorts) | = true, use linear relation between m_flow and dp for any flow rate |
| Real[nPorts] | deltaM (from TwoNPortsFlowResistanceParameters) | fill(0.1, nPorts) | Fraction of nominal flow rate where flow transitions to laminar |
| Dynamics › Conservation equations | |||
| Modelica.Fluid.Types.Dynamics | energyDynamics (from PartialStorage) | Modelica.Fluid.Types.Dynamics.DynamicFreeInitial | Type of energy balance: dynamic (3 initialization options) or steady state |
| Initialization | |||
| Medium.AbsolutePressure | p_start (from PartialStorage) | Medium.p_default | Start value of pressure |
| Modelica.Units.SI.Temperature[nSeg] | TFlu_start (from PartialStorage) | TGro_start | Start value of fluid temperature |
| Initialization › Soil | |||
| Modelica.Units.SI.Temperature | TExt0_start (from PartialStorage) | 283.15 | Initial far field temperature |
| Modelica.Units.SI.Temperature[nSeg] | TExt_start (from PartialStorage) | {if z[i] >= z0 then TExt0_start + (z[i] - z0)*dT_dz else TExt0_start for i in 1:nSeg} | Temperature of the undisturbed ground |
| Initialization › Filling material | |||
| Modelica.Units.SI.Temperature[nSeg] | TGro_start (from PartialStorage) | TExt_start | Start value of grout temperature |
| Initialization › Temperature profile | |||
| Modelica.Units.SI.Height | z0 (from PartialStorage) | 10 | Depth below which the temperature gradient starts |
| Real | dT_dz (from PartialStorage) | 0.01 | Vertical temperature gradient of the undisturbed soil for h below z0 |
Connectors
| Type | Name | Default | Description |
|---|---|---|---|
| Modelica.Fluid.Interfaces.FluidPort_a[nPorts] | port_a (from PartialTwoNPorts) | Fluid connector a (positive design flow direction is from port_a to port_b) | |
| Modelica.Fluid.Interfaces.FluidPort_b[nPorts] | port_b (from PartialTwoNPorts) | Fluid connector b (positive design flow direction is from port_a to port_b) | |
| Modelica.Blocks.Interfaces.RealOutput[nZon] | TBorAve (from PartialStorage) | Average borehole wall temperature in the borefield | |
| Modelica.Blocks.Interfaces.RealOutput[nZon] | QBorAve (from PartialStorage) | Average (per borehole) heat transfer rate in each zone |
Components
| Type | Name | Default | Description |
|---|---|---|---|
| Modelica.Units.SI.MassFlowRate[nPorts] | m_flow (from PartialTwoNPortsInterface) | port_a[:].m_flow | Mass flow rate from port_a to port_b (m_flow > 0 is design flow direction) |
| Modelica.Units.SI.PressureDifference[nPorts] | dp (from PartialTwoNPortsInterface) | port_a[:].p - port_b[:].p | Pressure difference between port_a and port_b |
| Medium.ThermodynamicState[nPorts] | sta_a (from PartialTwoNPortsInterface) | if allowFlowReversal then Medium.setState_phX(port_a.p, noEvent(actualStream(port_a.h_outflow)), noEvent(actualStream(port_a.Xi_outflow))) else Medium.setState_phX(port_a.p, noEvent(inStream(port_a.h_outflow)), noEvent(inStream(port_a.Xi_outflow))) | Medium properties in port_a |
| Medium.ThermodynamicState[nPorts] | sta_b (from PartialTwoNPortsInterface) | if allowFlowReversal then Medium.setState_phX(port_b.p, noEvent(actualStream(port_b.h_outflow)), noEvent(actualStream(port_b.Xi_outflow))) else Medium.setState_phX(port_b.p, noEvent(port_b.h_outflow), noEvent(port_b.Xi_outflow)) | Medium properties in port_b |
| Buildings.Fluid.Geothermal.Borefields.BaseClasses.Boreholes.BaseClasses.PartialBorehole[nZon] | borHol (from PartialStorage) | ||
| Buildings.Fluid.Geothermal.ZonedBorefields.BaseClasses.HeatTransfer.GroundTemperatureResponse | groTemRes (from PartialStorage) | Ground thermal response |
Revisions
-
February 2024, by Massimo Cimmino:
First implementation.