Re: [EnergyPlus_Support] Energy storage into a wall

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

Have you tried a steady-state design-day case to make sure that everything 
balances as expected?  Perhaps there is a missing term in your formulation of 
the exterior surface heat balance.

Mike


On 8 Feb 2008 at 10:37, Michela wrote:

> Hello!
> I?m trying to evaluate the role of thermal 
> inertia of an exterior wall of a very simple 
> building in purchased air simulation. The idea is 
> to calculate the energy stored into and released by the wall, say DE.
> 
> For this I use ?conduction into the wall, qko? 
> and ?conduction from outside, qki?, like defined 
> in the manual Engineering Reference page 35 and 48 respectively.
> 
> I calculate qko by summing the energy flows at 
> the exterior surface as it is described on page 
> 35 of the Engineering Reference:
> qasol + qLWR + qconv ? qko = 0
> 
> Instead I obtain qki from the Energy Plus 
> outputs: ?Opaque Surface Inside Face Conduction 
> Gain[W](Hourly)? and ?Opaque Surface Inside Face Conduction Loss[W](Hourly)?.
> 
> I assume the following sign convention:
> qko >0 if the flow enters into the wall
> qki >0 if the flow enters into the internal zone.
> 
> Then the internal energy variation of the wall in a time step is calculated as:
> DE = (qko ? qki) Dt
> 
> It should be that if DE < 0 the wall is loosing 
> energy, while if DE > 0 the wall is storing energy.
> Then I expected to find that DE changes its sign 
> during the day, showing the heat storage and 
> realease. But on the contrary during the summer 
> period I observed that the wall always has a 
> negative energy variation. The wall has more loss 
> then gain. But, looking at the outside and inside 
> surface temperatures of the wall, they are not constantly decreasing.
> 
> How do you feel with this result? Did anybody 
> ever try a similar analysis? May you suggest any 
> other way to study the energy storage into the wall?
> 
> Thanks a lot for any help!
> 
> Michela
> 
> 
> 
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> 
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> 
> 
> 
> 
> 


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





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