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
FixedBoundary	Boundary source component
MassFlowSource_T	Ideal flow source that produces a prescribed mass flow with prescribed temperature, mass fraction and trace substances
MassFlowSource_h	Ideal flow source that produces a prescribed mass flow with prescribed specific enthalpy, mass fraction 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_CpLowRise	Boundary that takes weather data as an input and computes wind pressure for low-rise buildings
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
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).

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, composition and trace substances.

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 Modelica.Fluid.Sources.BaseClasses.PartialSource (Partial component source with one fluid connector).

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

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, composition and trace substances.

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 Modelica.Fluid.Sources.BaseClasses.PartialSource (Partial component source with one fluid connector).

Parameters

Connectors

Modelica definition

Buildings.Fluid.Sources.FixedBoundary

Boundary source component

Information

This model defines constant values for boundary conditions:

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

Note, that boundary temperature, density, 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 Modelica.Fluid.Sources.BaseClasses.PartialSource (Partial component source with one fluid connector).

Parameters

Connectors

Modelica definition

Buildings.Fluid.Sources.MassFlowSource_T

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

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 Modelica.Fluid.Sources.BaseClasses.PartialSource (Partial component 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, mass fraction and trace substances

Information

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

• 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 temperature, composition and trace substances.

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 Modelica.Fluid.Sources.BaseClasses.PartialSource (Partial component source with one fluid connector).

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_CpLowRise

Boundary that takes weather data as an input and computes wind pressure for low-rise buildings

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_Cp should be used that takes the wind pressure coefficient as an input or parameter.

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.

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.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.

Extends from Modelica.Fluid.Sources.BaseClasses.PartialSource (Partial component source with one fluid connector).

Parameters

Connectors

Modelica definition