modelExtLWR
Information
Calculation of long wavelength radiation exchanges with the sky and the environment
Hypothesis and equations
The solar flux with long wavelength radiation has two sources : the environment and the sky. Different hypothesis have been made :
- The flux from the sky is supposed isotropic.
- The exchanges between the wall, the sky and the environment are supposed to depend only on the tilt and the long wavelength emissivity.
- The sky and the environment are supposed to be isothermal black bodies.
The radiative net fux exchanged between a wall and the outside is calculated with the function below :
Where 
is the Stefan-Boltzmann constant.
Bibliography
TF1 CLIM2000
Instructions for use
Typical values for epsilon (from BodyRadiation model) :
aluminium, polished 0.04 copper, polished 0.04 gold, polished 0.02 paper 0.09 rubber 0.95 silver, polished 0.02 wood 0.85..0.9
It is possible to calculate the long wavelength exchanges with the soil using the boolean backLWR = true.
Known limits / Use precautions
As this model is used in a wall model with convective and radiatives exchanges on its surface, care must be taken to ensure that the outside superficial heat exchange coefficient is a real convective heat exchange coefficient instead of integrating the long wavelength radiation.
Validations
Validated model (analytical verification + verification of the coherence of the exchanged fluxes profile) - Aurélie Kaemmerlen 09/2011
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Licensed by EDF under a 3-clause BSD-license
Copyright © EDF 2009 - 2023
BuildSysPro version 3.6.0
Author : Aurélie KAEMMERLEN, EDF (2011)
Initial model : BodyRadiation, Anton Haumer, Copyright © Modelica Association, Michael Tiller and DLR.
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Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| Boolean | backLWR | false | Model used to calculate exchanges with the soil and the environnement? |
| Boolean | use_incl_in | false | Prescribed or fixed tilt of the surface relative to the horizontal |
| Modelica.Units.SI.Area | S | 1 | Surface |
| Real | eps | 0.5 | Emissivity |
| Real | incl | 30 | Tilt of the surface relative to the horizontal - toward the ground=180°, toward the sky=0°, vertical=90° |
| Boolean | GLO_env | true | Integration of long wavelength radiation (infrared) toward the environment |
| Boolean | GLO_ciel | true | Integration of long wavelength radiation (infrared) toward the sky |
Connectors
| Type | Name | Default | Description |
|---|---|---|---|
| BuildSysPro.BaseClasses.HeatTransfer.Interfaces.HeatPort_a | T_sky | Sky temperature | |
| BuildSysPro.BaseClasses.HeatTransfer.Interfaces.HeatPort_a | T_ext | Outside temperature (of the environment) | |
| BuildSysPro.BaseClasses.HeatTransfer.Interfaces.HeatPort_b | Ts_ext | Outside temperature at the wall surface | |
| Modelica.Blocks.Interfaces.RealInput | incl_in | Tilt of the surface relative to the horizontal - toward the ground=180°, toward the sky=0°, vertical=90° |
Components
| Type | Name | Default | Description |
|---|---|---|---|
| BuildSysPro.BaseClasses.HeatTransfer.Components.BodyRadiation | GLOenv | Long wavelength exchanges with the environment | |
| BuildSysPro.BaseClasses.HeatTransfer.Components.BodyRadiation | GLOciel | Long wavelength exchanges with the sky |
Revisions
Stéphanie Froidurot 07/2019 : Adding the possibility to use fixed (parameter) or prescribed (input) tilt, controlled by a boolean (use_incl_in). Adding the possibility to calculate radiative exchanges with the soil (tilt = 180 - incl), controlled by a boolean (backLWR).