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RE: [EnergyPlus_Support] Exterior Radiative Heat Transfer Coefficients




Peter, 
 
I think you have it right.  These are linearized radiation coefficients that are comparable to convection coefficients.
For example the coefficient for sky is calculated using,
 
h_rad = Sigma * Emittance * View_Factor * ((TSurf**4)-(TSky**4))/(TSurf-TSky)
 
Brent
 

-----Original Message-----
From: Peter G. Loutzenhiser [mailto:post@xxxxxxxxxxx]
Sent: Thursday, December 02, 2004 10:03 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Exterior Radiative Heat Transfer Coefficients


Hello all,

I am looking some of the inputs for output variables in EnergyPlus and have 
come across three outputs that I am not exactly certain what they mean.  They 
include 1) Surface Ext Rad to Air Coeff, 2) Surface Ext Rad to Sky Coeff, and 
3) Surface Ext Ground Coeff.  I have looked at the Engineering Manuel which 
explains the calculation method thoroughly,but not the coefficients.  Are these 
coefficients used to calculate the impact of radiation in a form similar to the 
exterior convective heat transfer coefficient?  Is it reasonable to define the 
radiative component of heat transfer as the sum of these values and make the 
following calculation?:

qrad=h_rad*surface_area(T_outside_temp-T_exterior_surface_temp)

Or are the coefficients defined in a different way?

Thank you so much for your help.

Peter





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