modelOutside_CpLowRise
Extends from Buildings.Fluid.Sources.BaseClasses.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. 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 Cp0 = 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 Cp
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 = pw + Cp 1 ⁄ 2 v2 ρ,
where pw 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 Cp,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.
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| Integer | nPorts (from PartialAirSource) | 0 | Number of ports |
| Boolean | use_C_in (from Outside) | false | Get the trace substances from the input connector |
| Medium.ExtraProperty[Medium.nC] | C (from Outside) | fill(0, Medium.nC) | Fixed values of trace substances |
| Real | Cp0 | 0.6 | Wind pressure coefficient for wind normal to wall |
| Real | s | Side ratio, s=length of this wall/length of adjacent wall | |
| Modelica.Units.SI.Angle | azi | Surface azimuth (South:0, West:pi/2) | |
| Advanced | |||
| Boolean | verifyInputs (from PartialAirSource) | false | Set to true to stop the simulation with an error if the medium temperature is outside its allowable range |
Connectors
| Type | Name | Default | Description |
|---|---|---|---|
| Modelica.Fluid.Interfaces.FluidPorts_b[nPorts] | ports (from PartialAirSource) | Fluid ports | |
| Modelica.Blocks.Interfaces.RealInput[Medium.nC] | C_in (from Outside) | Prescribed boundary trace substances | |
| Buildings.BoundaryConditions.WeatherData.Bus | weaBus (from Outside) | Bus with weather data |
Components
| Type | Name | Default | Description |
|---|---|---|---|
| Modelica.Units.SI.Angle | alpha | winDir - surOut | Wind incidence angle (0: normal to wall) |
| Real | CpAct | Buildings.Airflow.Multizone.BaseClasses.windPressureLowRise(Cp0 = Cp0, alpha = alpha, G = G) | Actual wind pressure coefficient |
| Modelica.Units.SI.Pressure | pWin | 0.5*CpAct*d*vWin*vWin | Change in pressure due to wind force |
Revisions
-
April 4, 2023, by Michael Wetter:
Removed use of non-existent parameter in annotation.
This is for IBPSA, #1724. -
February 2, 2022, by Michael Wetter:
Revised implementation.
This is for IBPSA, #1436. -
Jun 28, 2021, by Klaas De Jonge:
Documentation changes to explain the difference with Buildings.Fluid.Sources.Outside_CpData. -
January 26, 2016, by Michael Wetter:
Addedunitandquantityattributes. -
October 26, 2011 by Michael Wetter:
First implementation.