Re: [EnergyPlus_Support] longwave radiation from the environment

["friedl decock" <friedl.decock@xxxxxxxxx>]

So the report variable ' Surface Ext *Convection* Coeff[W/m2-K](TimeStep)'
for simple convection algorithm means the *total* exterior heat transfer
coefficient (radiant and convective) and is independent from the surface
emissivity.

I tried already all the other convection algorithms (detailed, TARP,
DOE-2...), but I still get zero for the radiant heat coefficients. I also
have the impression that the convective heat transfer coefficient stays the
same as calculated with the simple convection algorithm. Do I need to set
other settings beside the 'outside convection algorithm'?

Thank you for your help,
Friedl

On 9/17/07, Michael J. Witte <mjwitte@xxxxxxxx> wrote:
>
>   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 <EnergyPlus-Support%40gard.com>
>
> 
>


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