modelOutside_CpData
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 ports ports.
The pressure p at the fluid ports is computed as:
p = pw + Cp,act Cs v2 ρ ⁄ 2,
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.
The wind pressure coefficient Cp,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 Cp,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 Cs 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.
| Wind from North: 0 0° | ||
| Wind from West: 3π/2 270° | Wind from East: π/2 90° | |
| Wind from South: π 180° |
For the surface azimuth azi, the specification from
Buildings.Types.Azimuth is
used, which is as shown in the table below.
| Wall facing north: π 180° | ||
| Wall facing West: π/2 90° | Wall facing east: 3π/2 270° | |
| Wall facing South: 0; 0° |
Related model
This model differs from Buildings.Fluid.Sources.Outside_CpLowRise by the calculation of the wind pressure coefficient Cp,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.
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 |
| Modelica.Units.SI.Angle | azi | Surface azimuth (South:0, West:pi/2) | |
| Modelica.Units.SI.Angle[:] | incAngSurNor | Wind incidence angles, relative to the surface normal (normal=0), first point must be 0, last smaller than 2 pi(=360 deg) | |
| Real[:] | Cp | Cp values at the corresponding incAngSurNor | |
| Real | Cs | 1 | Wind speed modifier |
| 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.Pressure | pWin | Cs*0.5*CpAct*d*vWin*vWin | Change in pressure due to wind force |
| Real | CpAct | Buildings.Airflow.Multizone.BaseClasses.windPressureProfile(alpha = alpha, incAngTab = incAngExt, CpTab = CpExt, d = deri) | Actual wind pressure coefficient |
| Modelica.Units.SI.Angle | alpha | winDir - surOut | Wind incidence angle (0: normal to wall) |
Revisions
-
February 2, 2022, by Michael Wetter:
Revised implementation.
This is for IBPSA, #1436. -
Apr 6, 2021, by Klaas De Jonge:
First implementation.