Re: [EnergyPlus_Support] longwave radiation from the environment

["Michael J. Witte" <mjwitte@xxxxxxxx>]

The exterior radiant coefficients will be zero when OUTSIDE CONVECTION is set 
to "simple".  The "simple" convection algorithms use a combined convection-
radiation coefficient and additional radiant transfer is not modeled.  

To see values in these variables, use the "Detailed" OUTSIDE CONVECTION option. 
 These are the "simple" and "detailed" methods referred to in the TARP manual, 
however, the coefficients may be slightly different than what is found in the 
TARP manual.  The detailed convection model is based on ASHRAE equations.

Mike


On 17 Sep 2007 at 10:58, friedl decock wrote:

> I'm trying to get the different heat fluxes through a wall out of a
> simulation.
> Everything seems to be fine for the interior surface heat balance. But I
> encounter some problems with the outside surface heat balance, especially
> with the longwave radiation from the environment.
> 
> 1. If I try to calculate qLWR with the formulas on p.36 (in the engineering
> reference document) and with the output from a simulation (surface temperatures,
> sky temperature, outside air temperature), there is a big difference between the
> 'calculated qLWR' and the flux out of the simulation ( = [Surface Inside Face
> Conduction] - [qSOL] - [qconv,exterior]). (There is no thermal storage (density
> = specific heat = 0)).
> 
> 2. If I'm asking for the report variables: Surface Ext Rad to Air Coeff,
> Surface Ext Rad to Sky Coeff, Surface Ext Rad to Ground Coeff, they are
> always zero. Do you need to do something special to get those report
> variables?
> 
> 3. In the engineering reference document p.60 basic heat balance:
> "TARP includes four possible representations for the basic outside surface
> heat balance. The first two depend on which of the optimal surface
> conductance algorithms the user selects. The simple outside surface
> conductance that includes both the convective and thermal interchange
> between the surface and the environment in a single coefficient, " ... " The
> detailed outside surface conductance model considers convection and radiation
> interchange with the sky and with the ground as seperate factors."
> 
> 3a. How can you chose the optimal surface conductance algorithm?
> 3b. What's the value of the single coefficient? Does it take the emissivity of
> the surface into account? 3c. The detailed outside surface conductance seems to
> be almost the same as mentioned on p.35, accept that I don't see the radiative
> heat transfer coeff to the air in figure 28 on p.62. (HA = outside convection
> coefficient) (Or is HA a single value for radiation and convection?)


========================================================
Michael J. Witte, GARD Analytics, Inc.
EnergyPlus Testing and Support      
EnergyPlus-Support@xxxxxxxx





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