Buildings.DHC.Networks.Pipes

Package containing pipe models used within district network modeling

Information

This package contains pipe models specific for distribution networks.

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

Package Content

Name	Description
PipeAutosize	Pipe model parameterized with pressure drop per pipe length
PipeStandard	Pipe model parameterized with hydraulic diameter
Validation	Validation models for Pipes

Buildings.DHC.Networks.Pipes.PipeAutosize

Pipe model parameterized with pressure drop per pipe length

Buildings.DHC.Networks.Pipes.PipeAutosize

Information

This model is similar to Buildings.Fluid.FixedResistances.HydraulicDiameter except for the modifications below which allow to use this model for computing the hydraulic diameter at initialization, based on the pressure drop per pipe length at nominal flow rate.

The parameter v_nominal is computed based on the nominal flow rate.
The equation dp_nominal = fac*dpStraightPipe_nominal is solved at initialization for the hydraulic diameter dh.
The parameter dp_nominal is assigned a value that does not need to be computed at initialization. This is required per Modelica specification because the structural parameter computeFlowResistance depends on dp_nominal and must be evaluated at compile time.

Extends from Buildings.Fluid.FixedResistances.PressureDrop (Fixed flow resistance with dp and m_flow as parameter).

Parameters

Type	Name	Default	Description
replaceable package Medium		PartialMedium	Medium in the component
Length	dh		Hydraulic diameter (assuming a round cross section area) [m]
Real	dp_length_nominal	250	Pressure drop per pipe length at nominal flow rate [Pa/m]
Length	length		Length of the pipe [m]
Real	ReC	4000	Reynolds number where transition to turbulence starts
Length	roughness	2.5e-5	Absolute roughness of pipe, with a default for a smooth steel pipe (PE100: 7E-6) [m]
Real	fac	2	Factor to take into account resistance of bends etc., fac=dp_nominal/dpStraightPipe_nominal
Nominal condition
MassFlowRate	m_flow_nominal		Nominal mass flow rate [kg/s]
PressureDifference	dp_nominal	dp_length_nominal*length	Pressure drop at nominal mass flow rate [Pa]
Transition to laminar
Real	deltaM	eta_defaultdh/4Modelica.Co...	Fraction of nominal mass flow rate where transition to turbulent occurs
Assumptions
Boolean	allowFlowReversal	true	= false to simplify equations, assuming, but not enforcing, no flow reversal
Advanced
Diagnostics
Boolean	show_T	false	= true, if actual temperature at port is computed
Boolean	from_dp	false	= true, use m_flow = f(dp) else dp = f(m_flow)
Boolean	linearized	false	= true, use linear relation between m_flow and dp for any flow rate

Connectors

Type	Name	Description
FluidPort_a	port_a	Fluid connector a (positive design flow direction is from port_a to port_b)
FluidPort_b	port_b	Fluid connector b (positive design flow direction is from port_a to port_b)

Modelica definition

model PipeAutosize "Pipe model parameterized with pressure drop per pipe length" extends Buildings.Fluid.FixedResistances.PressureDrop( final deltaM = eta_default*dh/4*Modelica.Constants.pi*ReC/m_flow_nominal_pos, final dp_nominal = dp_length_nominal*length); parameter Modelica.Units.SI.Length dh( fixed=false, start=0.01, min=0.001) "Hydraulic diameter (assuming a round cross section area)"; parameter Real dp_length_nominal(final unit="Pa/m") = 250 "Pressure drop per pipe length at nominal flow rate"; parameter Modelica.Units.SI.Length length "Length of the pipe"; parameter Real ReC(min=0) = 4000 "Reynolds number where transition to turbulence starts"; parameter Modelica.Units.SI.Length roughness(min=0) = 2.5e-5 "Absolute roughness of pipe, with a default for a smooth steel pipe (PE100: 7E-6)"; parameter Real fac(min=1) = 2 "Factor to take into account resistance of bends etc., fac=dp_nominal/dpStraightPipe_nominal"; final parameter Modelica.Units.SI.PressureDifference dpStraightPipe_nominal( displayUnit="Pa")=Modelica.Fluid.Pipes.BaseClasses.WallFriction.Detailed.pressureLoss_m_flow( m_flow=m_flow_nominal, rho_a=rho_default, rho_b=rho_default, mu_a=mu_default, mu_b=mu_default, length=length, diameter=dh, roughness=roughness, m_flow_small=m_flow_small) "Pressure loss of a straight pipe at m_flow_nominal"; Modelica.Units.SI.Velocity v = m_flow/(rho_default*ARound) "Flow velocity (assuming a round cross section area)"; protected parameter Modelica.Units.SI.Area ARound = dh^2*Modelica.Constants.pi/4 "Cross sectional area (assuming a round cross section area)"; parameter Modelica.Units.SI.Velocity v_nominal = m_flow_nominal/(rho_default* ARound) "Velocity at m_flow_nominal (used to compute default value for hydraulic diameter dh)"; parameter Medium.ThermodynamicState state_default= Medium.setState_pTX( T=Medium.T_default, p=Medium.p_default, X=Medium.X_default[1:Medium.nXi]) "Default state"; parameter Modelica.Units.SI.Density rho_default=Medium.density(state_default) "Density at nominal condition"; parameter Modelica.Units.SI.DynamicViscosity mu_default = Medium.dynamicViscosity(state_default) "Dynamic viscosity at nominal condition"; initial equation dp_nominal = fac*dpStraightPipe_nominal; end PipeAutosize;

Buildings.DHC.Networks.Pipes.PipeStandard

Pipe model parameterized with hydraulic diameter

Buildings.DHC.Networks.Pipes.PipeStandard

Information

This model is similar to Buildings.Fluid.FixedResistances.HydraulicDiameter except that a binding equation is provided to compute the nominal fluid velocity from the hydraulic diameter (as opposed to the hydraulic diameter being computed from the nominal fluid velocity in the original model).

Extends from Buildings.Fluid.FixedResistances.HydraulicDiameter (Fixed flow resistance with hydraulic diameter and m_flow as parameter).

Parameters

Type	Name	Default	Description
replaceable package Medium		PartialMedium	Medium in the component
Length	dh	sqrt(4*m_flow_nominal/rho_de...	Hydraulic diameter (assuming a round cross section area) [m]
Length	length		Length of the pipe [m]
Real	ReC	4000	Reynolds number where transition to turbulence starts
Length	roughness	2.5e-5	Absolute roughness of pipe, with a default for a smooth steel pipe (dummy if use_roughness = false) [m]
Real	fac	2	Factor to take into account resistance of bends etc., fac=dp_nominal/dpStraightPipe_nominal
Nominal condition
MassFlowRate	m_flow_nominal		Nominal mass flow rate [kg/s]
Velocity	v_nominal	m_flow_nominal*4/(rho_defaul...	Velocity at m_flow_nominal (used to compute default value for hydraulic diameter dh) [m/s]
Assumptions
Boolean	allowFlowReversal	true	= false to simplify equations, assuming, but not enforcing, no flow reversal
Advanced
Diagnostics
Boolean	show_T	false	= true, if actual temperature at port is computed
Boolean	from_dp	false	= true, use m_flow = f(dp) else dp = f(m_flow)
Boolean	linearized	false	= true, use linear relation between m_flow and dp for any flow rate

Connectors

Type	Name	Description
FluidPort_a	port_a	Fluid connector a (positive design flow direction is from port_a to port_b)
FluidPort_b	port_b	Fluid connector b (positive design flow direction is from port_a to port_b)

Modelica definition

model PipeStandard "Pipe model parameterized with hydraulic diameter" extends Buildings.Fluid.FixedResistances.HydraulicDiameter( dp(nominal = 1E5), final linearized = false, final v_nominal = m_flow_nominal*4/(rho_default * dh^2 * Modelica.Constants.pi)); end PipeStandard;