Buildings.Fluid.Sources

Package with boundary condition models

Information

Package Sources contains generic sources for fluid connectors to define fixed or prescribed ambient conditions.

Extends from Modelica.Icons.SourcesPackage (Icon for packages containing sources).

Package Content

Name	Description
Boundary_pT	Boundary with prescribed pressure, temperature, composition and trace substances
Boundary_ph	Boundary with prescribed pressure, specific enthalpy, composition and trace substances
MassFlowSource_T	Ideal flow source that produces a prescribed mass flow with prescribed temperature, composition and trace substances
MassFlowSource_WeatherData	Ideal flow source that produces a prescribed mass flow with prescribed trace substances, outside specific enthalpy and mass fraction
MassFlowSource_h	Ideal flow source that produces a prescribed mass flow with prescribed specific enthalpy, composition and trace substances
Outside	Boundary that takes weather data, and optionally trace substances, as an input
Outside_Cp	Boundary that takes weather data, and optionally the wind pressure coefficient and trace substances, as an input
Outside_CpData	Boundary that takes weather data as an input and computes the wind pressure from a given wind pressure profile
Outside_CpLowRise	Boundary that takes weather data as an input and computes the wind pressure for low-rise buildings based on the equation from Swami and Chandra (1987)
PropertySource_T	Model for overriding fluid properties that flow through the component, using temperature input
PropertySource_h	Model for overriding fluid properties that flow through the component, using specific enthalpy input
TraceSubstancesFlowSource	Source with mass flow that does not take part in medium mass balance (such as CO2)
Examples	Collection of models that illustrate model use and test models
Validation	Collection of validation models
BaseClasses	Package with base classes for Buildings.Fluid.Sources

Buildings.Fluid.Sources.Boundary_pT

Boundary with prescribed pressure, temperature, composition and trace substances

Information

Defines prescribed values for boundary conditions:

• Prescribed boundary pressure.
• Prescribed boundary temperature.
• Boundary composition (only for multi-substance or trace-substance flow).

Typical use and important parameters

If use_p_in is false (default option), the p parameter is used as boundary pressure, and the p_in input connector is disabled; if use_p_in is true, then the p parameter is ignored, and the value provided by the input connector is used instead.

The same applies to the temperature T, composition X_i or X and trace substances C.

Options

Instead of using Xi_in (the independent composition fractions), the advanced tab provides an option for setting all composition fractions using X_in. use_X_in and use_Xi_in cannot be used at the same time.

Parameter verifyInputs can be set to true to enable a check that verifies the validity of the used temperatures and pressures. This removes the corresponding overhead from the model, which is a substantial part of the overhead of this model. See #882 for more information.

Note, that boundary temperature, mass fractions and trace substances have only an effect if the mass flow is from the boundary into the port. If mass is flowing from the port into the boundary, the boundary definitions, with exception of boundary pressure, do not have an effect.

Extends from Buildings.Fluid.Sources.BaseClasses.PartialSource_Xi_C (Partial component source with parameter definitions for Xi and C).

Parameters

Connectors

Modelica definition

Buildings.Fluid.Sources.Boundary_ph

Boundary with prescribed pressure, specific enthalpy, composition and trace substances

Information

Defines prescribed values for boundary conditions:

• Prescribed boundary pressure.
• Prescribed boundary specific enthalpy.
• Boundary composition (only for multi-substance or trace-substance flow).

Typical use and important parameters

If use_p_in is false (default option), the p parameter is used as boundary pressure, and the p_in input connector is disabled; if use_p_in is true, then the p parameter is ignored, and the value provided by the input connector is used instead.

The same applies to the specific enthalpy h, composition X_i or X and trace substances C.

Options

Instead of using Xi_in (the independent composition fractions), the advanced tab provides an option for setting all composition fractions using X_in. use_X_in and use_Xi_in cannot be used at the same time.

Parameter verifyInputs can be set to true to enable a check that verifies the validity of the used specific enthalpy and pressures. This removes the corresponding overhead from the model, which is a substantial part of the overhead of this model. See #882 for more information.

Note, that boundary specific enthalpy, mass fractions and trace substances have only an effect if the mass flow is from the boundary into the port. If mass is flowing from the port into the boundary, the boundary definitions, with exception of boundary pressure, do not have an effect.

Extends from Buildings.Fluid.Sources.BaseClasses.PartialSource_Xi_C (Partial component source with parameter definitions for Xi and C).

Parameters

Connectors

Modelica definition

Buildings.Fluid.Sources.MassFlowSource_T

Ideal flow source that produces a prescribed mass flow with prescribed temperature, composition and trace substances

Information

Models an ideal flow source, with prescribed values of flow rate, temperature, composition and trace substances:

• Prescribed mass flow rate.
• Prescribed temperature.
• Boundary composition (only for multi-substance or trace-substance flow).

If use_m_flow_in is false (default option), the m_flow parameter is used as boundary pressure, and the m_flow_in input connector is disabled; if use_m_flow_in is true, then the m_flow parameter is ignored, and the value provided by the input connector is used instead.

The same applies to the temperature T, composition X_i or X and trace substances C.

Options

Instead of using Xi_in (the independent composition fractions), the advanced tab provides an option for setting all composition fractions using X_in. use_X_in and use_Xi_in cannot be used at the same time.

Parameter verifyInputs can be set to true to enable a check that verifies the validity of the used temperature and pressures. This removes the corresponding overhead from the model, which is a substantial part of the overhead of this model. See #882 for more information.

Note, that boundary temperature, mass fractions and trace substances have only an effect if the mass flow is from the boundary into the port. If mass is flowing from the port into the boundary, the boundary definitions, with exception of boundary flow rate, do not have an effect.

Extends from Buildings.Fluid.Sources.BaseClasses.PartialSource_Xi_C (Partial component source with parameter definitions for Xi and C).

Parameters

Connectors

Modelica definition

Buildings.Fluid.Sources.MassFlowSource_WeatherData

Ideal flow source that produces a prescribed mass flow with prescribed trace substances, outside specific enthalpy and mass fraction

Information

Models an ideal flow source, with prescribed values of flow rate and trace substances, with temperature and specific enthalpy from outside:

• Prescribed mass flow rate.
• Boundary composition (trace-substance flow).
• Outside specific enthalpy.
• Multi-substance composition (e.g. water vapor) from outside.

If use_m_flow_in is false (default option), the m_flow parameter is used as boundary flow rate, and the m_flow_in input connector is disabled; if use_m_flow_in is true, then the m_flow parameter is ignored, and the value provided by the input connector is used instead.

The same applies to the trace substances.

The Buildings.Utilities.Psychrometrics.X_pTphi block is used with the input data including pAtm, TDryBul, relHum from weather bus weaBus, to calculate X.

The same applies to the specific enthalpy.

Note, that boundary temperature, mass fractions and trace substances have only an effect if the mass flow is from the boundary into the port. If mass is flowing from the port into the boundary, the boundary definitions, with exception of boundary flow rate, do not have an effect.

Extends from Buildings.Fluid.Sources.BaseClasses.PartialAirSource (Partial component air source with one fluid connector).

Parameters

Connectors

Modelica definition

Buildings.Fluid.Sources.MassFlowSource_h

Ideal flow source that produces a prescribed mass flow with prescribed specific enthalpy, composition and trace substances

Information

Models an ideal flow source, with prescribed values of flow rate, specific enthalpy, composition and trace substances:

• Prescribed mass flow rate.
• Prescribed specific enthalpy.
• Boundary composition (only for multi-substance or trace-substance flow).

If use_m_flow_in is false (default option), the m_flow parameter is used as boundary pressure, and the m_flow_in input connector is disabled; if use_m_flow_in is true, then the m_flow parameter is ignored, and the value provided by the input connector is used instead.

The same applies to the specific enthalpy h, composition X_i or X and trace substances C.

Options

Instead of using Xi_in (the independent composition fractions), the advanced tab provides an option for setting all composition fractions using X_in. use_X_in and use_Xi_in cannot be used at the same time.

Parameter verifyInputs can be set to true to enable a check that verifies the validity of the used specific enthalpy and pressures. This removes the corresponding overhead from the model, which is a substantial part of the overhead of this model. See #882 for more information.

Note, that boundary specific enthalpy, mass fractions and trace substances have only an effect if the mass flow is from the boundary into the port. If mass is flowing from the port into the boundary, the boundary definitions, with exception of boundary flow rate, do not have an effect.

Extends from Buildings.Fluid.Sources.BaseClasses.PartialSource_Xi_C (Partial component source with parameter definitions for Xi and C).

Parameters

Connectors

Modelica definition

Buildings.Fluid.Sources.Outside

Boundary that takes weather data, and optionally trace substances, as an input

Information

This model describes boundary conditions for pressure, enthalpy, and species concentration that can be obtained from weather data.

To use this model, connect weather data from Buildings.BoundaryConditions.WeatherData.ReaderTMY3 to the port weaBus of this model. This will cause the medium of this model to be at the pressure that is obtained from the weather file, and any flow that leaves this model to be at the temperature and humidity that are obtained from the weather data.

If the parameter use_C_in is false (default option), the C parameter is used as the trace substance for flow that leaves the component, and the C_in input connector is disabled; if use_C_in is true, then the C parameter is ignored, and the value provided by the input connector is used instead.

Note that boundary temperature, mass fractions and trace substances have only an effect if the mass flow is from the boundary into the port. If mass is flowing from the port into the boundary, the boundary definitions, with exception of boundary pressure, do not have an effect.

Extends from Buildings.Fluid.Sources.BaseClasses.Outside (Boundary that takes weather data, and optionally trace substances, as an input).

Parameters

Connectors

Modelica definition

Buildings.Fluid.Sources.Outside_Cp

Boundary that takes weather data, and optionally the wind pressure coefficient and trace substances, as an input

Information

This model describes boundary conditions for pressure, enthalpy, and species concentration that can be obtained from weather data. The model is identical to Buildings.Fluid.Sources.Outside, except that it allows adding the wind pressure to the pressure at the fluid port ports.

The pressure p at the port ports is computed as

p = p_w + C_p 1 ⁄ 2 v² ρ

where p_w is the atmospheric pressure from the weather bus, C_p is the wind pressure coefficient, v is the wind speed from the weather bus, and ρ is the fluid density. If use_Cp_in=true, then the wind pressure coefficient is obtained from the input connector Cp_in. Otherwise, it is set to the parameter Cp.

Extends from Buildings.Fluid.Sources.BaseClasses.Outside (Boundary that takes weather data, and optionally trace substances, as an input).

Parameters

Connectors

Modelica definition

Buildings.Fluid.Sources.Outside_CpData

Boundary that takes weather data as an input and computes the wind pressure from a given wind pressure profile

Information

This model describes boundary conditions for pressure, enthalpy, and species concentration that can be obtained from weather data. The model is identical to Buildings.Fluid.Sources.Outside, except that it adds the wind pressure to the pressure at the fluid ports ports.

The pressure p at the fluid ports is computed as:

p = p_w + C_p,act C_s v² ρ ⁄ 2,

where p_w is the atmospheric pressure from the weather bus, v is the wind speed from the weather bus, and ρ is the fluid density.

The wind pressure coefficient C_p,act is a function of the surface wind incidence angle and is defined relative to the surface azimuth (normal to the surface is 0). The wind incidence angle incAng is computed from the wind direction obtained from the weather file with the surface azimuth azi as the base of the angle. The relation between the wind pressure coefficient C_p,act and the incidence angle incAng is defined by a cubic hermite interpolation of the users table input. Typical table values can be obtained from the "AIVC guide to energy efficient ventilation", appendix 2 (1996). The default table is appendix 2, table 2.2, face 1.

The wind speed modifier C_s can be used to incorporate the effect of the surroundings on the local wind speed.

Definition of angles

The angles incAngSurNor for the wind incidence angle relative to the surface normal are measured counter-clock wise. The figure below shows an example entry, which is also used in the model Buildings.Fluid.Sources.Examples.Outside_CpData_Specification.

The wind incidence angle and surface azimuths are defined as follows: The wind indicience angle is obtained directly from the weather data bus weaBus.winDir. This variable contains the data from the weather data file that was read, such as a TMY3 file. In accordance to TMY3, the data is as shown in the table below.

For the surface azimuth azi, the specification from Buildings.Types.Azimuth is used, which is as shown in the table below.

Related model

This model differs from Buildings.Fluid.Sources.Outside_CpLowRise by the calculation of the wind pressure coefficient C_p,act. The wind pressure coefficient is defined by a user-defined table instead of a generalized equation such that it can be used for all building sizes and situations, for shielded buildings, and for buildings with non-rectangular shapes.

References

• M. W. Liddament, 1996, A guide to energy efficient ventilation. AIVC Annex V.

Extends from Buildings.Fluid.Sources.BaseClasses.Outside (Boundary that takes weather data, and optionally trace substances, as an input).

Parameters

Connectors

Modelica definition

Buildings.Fluid.Sources.Outside_CpLowRise

Boundary that takes weather data as an input and computes the wind pressure for low-rise buildings based on the equation from Swami and Chandra (1987)

Information

This model describes boundary conditions for pressure, enthalpy, and species concentration that can be obtained from weather data. The model is identical to Buildings.Fluid.Sources.Outside, except that it adds the wind pressure to the pressure at the fluid port ports. The correlation that is used to compute the wind pressure is based on Swami and Chandra (1987) and valid for low-rise buildings with rectangular shape. The same correlation is also implemented in CONTAM (Persily and Ivy, 2001). For other buildings, the model Buildings.Fluid.Sources.Outside_CpData or Buildings.Fluid.Sources.Outside_Cp should be used that takes the wind pressure coefficient as a parameter or an input.

The wind pressure coefficient is computed based on the side ratio of the walls, which is defined as

s = x ⁄ y

where x is the length of the wall that will be connected to this model, and y is the length of the adjacent wall. The wind direction is computed relative to the azimuth of this surface, which is equal to the parameter azi. The surface azimuth is defined in Buildings.Types.Azimuth. For example, if an exterior wall is South oriented, i.e., its outside-facing surface is towards South, use Buildings.Types.Azimuth.S.

Based on the surface azimuth, the wind direction and the side ratio of the walls, the model computes how much the wind pressure is attenuated compared to the reference wind pressure Cp0. The reference wind pressure Cp0 is a user-defined parameter, and must be equal to the wind pressure at zero wind incidence angle. Swami and Chandra (1987) recommend C_p0 = 0.6 for all low-rise buildings as this represents the average of various values reported in the literature. The computation of the actual wind pressure coefficient C_p is explained in the function Buildings.Airflow.Multizone.BaseClasses.windPressureLowRise that is called by this model.

The pressure p at the port ports is computed as

p = p_w + C_p 1 ⁄ 2 v² ρ,

where p_w is the atmospheric pressure from the weather bus, v is the wind speed from the weather bus, and ρ is the fluid density.

This model differs from Buildings.Fluid.Sources.Outside_CpData by the calculation of the wind pressure coefficient C_p,act. The wind pressure coefficient is defined by an equation in stead of a user-defined table. This model is only suited for low-rise rectangular buildings.

References

• Muthusamy V. Swami and Subrato Chandra. Procedures for Calculating Natural Ventilation Airflow Rates in Buildings. Florida Solar Energy Center, FSEC-CR-163-86. March, 1987. Cape Canaveral, Florida.
• Andrew K. Persily and Elizabeth M. Ivy. Input Data for Multizone Airflow and IAQ Analysis. NIST, NISTIR 6585. January, 2001. Gaithersburg, MD.

Extends from Buildings.Fluid.Sources.BaseClasses.Outside (Boundary that takes weather data, and optionally trace substances, as an input).

Parameters

Connectors

Modelica definition

Buildings.Fluid.Sources.PropertySource_T

Model for overriding fluid properties that flow through the component, using temperature input

Information

Model that changes the properties, but not the mass flow rate, of the fluid that passes through it.

If allowFlowReversal=true, then the properties are changed for both flow directions, i.e., from port_a to port_b and from port_b to port_a.

Typical use and important parameters

The fluid properties h, Xi and C are only modified when the corresponding boolean parameter use_T_in, use_Xi_in or use_C_in is set to true.

Dynamics

This model has no dynamics.

Extends from Buildings.Fluid.Sources.BaseClasses.PartialPropertySource (Partial model for overriding fluid properties that flow through the component).

Parameters

Connectors

Modelica definition

Buildings.Fluid.Sources.PropertySource_h

Model for overriding fluid properties that flow through the component, using specific enthalpy input

Information

Model that changes the properties, but not the mass flow rate, of the fluid that passes through it.

If allowFlowReversal=true, then the properties are changed for both flow directions, i.e., from port_a to port_b and from port_b to port_a.

Typical use and important parameters

The fluid properties h, Xi and C are only modified when the corresponding boolean parameter use_h_in, use_Xi_in or use_C_in is set to true.

Dynamics

This model has no dynamics.

Extends from Buildings.Fluid.Sources.BaseClasses.PartialPropertySource (Partial model for overriding fluid properties that flow through the component).

Parameters

Connectors

Modelica definition

Buildings.Fluid.Sources.TraceSubstancesFlowSource

Source with mass flow that does not take part in medium mass balance (such as CO2)

Information

This model can be used to inject trace substances into a system. The model adds a mass flow rate to its port with a trace substance concentration of 1.

Typical use and important parameters

A typical use of this model is to add carbon dioxide to room air, since the carbon dioxide concentration is typically so small that it need not be added to the room mass balance, and since the mass flow rate can be made small compared to the room volume if the medium that leaves this component has a carbon dioxide concentration of 1. The parameter substanceName must be set to the name of the substance that is injected into the fluid.

Note however that mixing volumes from the package Buildings.Fluid.MixingVolumes allow to directly add a trace substance mass flow rate, which is more efficient than using this model.

Parameters

Connectors

Modelica definition