.BuildSysPro.BaseClasses.HeatTransfer.Components.ExtLWR

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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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).