Re: [EnergyPlus_Support] Surface heat flux interpretation

[Edwin Lee <leeed2001@xxxxxxxxx>]

I believe the R-Value material still has some effective mass built in to ensure program stability.  This would cause variation.  Plot the E+ results with your steady state results for one day and see if there is a nice shift.  If the shift is there, the diff is probably the mass, if the shift is not the difference then there is something else going on.

To have better control of the mass, you could consider using a regular material and specifying smaller and smaller specific heats until the program gives you something close to the steady state answer you are requesting.  However, stability issues may again come into play.

Edwin

On Wed, Apr 22, 2009 at 5:02 AM, laurentvidal50 <laurent.vidal@xxxxxxxxx> wrote:

Hello,

Looking to a surface heat transfer I can't understand how heat flux is computed.

In Winter Design Day calc (T out = -3.1°C, T int = 22°C).
The U value surface-to-surface is 1 (one layer with a R=1 material only). My wall is 82.07 m2.

Convection algorithms are Simple for interior and exterior. I set no wind so that U convection int and out are those expected (Uc int = 3.076, Uc out = 8.23). At surface level output show me these values.

Now if I try to manually calculated heat transfer using convection given by outputs I can't get the Heat loss calculated by E+.
E+ give me 1194 W when I find 1434 W.

Where am I wrong?
May be this formula is not complete, does E+ uses another equation?
Heat = U-value-with-film x Surface x (T int - T out)

Thanks for any tip

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