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RE: [EnergyPlus_Support] Energy storage into a wall

I did this analysis in another way.

I modeled the same cell test with internal insulation, intermediate insulation and external insulation (changing the insulation layer position) then i reported monthly and annual Heating and cooling energy demand.

For Barcelona (Spain) there is only a very low difference (below 1%)

I did the same analysis changing the internal thermal inertia (adding or eliminating a very high insulation layer on adiabatic internal walls) and there is a high influence on energy demand about 11%

Conclusion thermal inertia on external wall has not influence but in internal walls they have a higher influence.

 

 

 

Josep Solé
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De: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] En nombre de Michela
Enviado el: viernes, 08 de febrero de 2008 10:37
Para: EnergyPlus_Support@xxxxxxxxxxxxxxx
Asunto: [EnergyPlus_Support] Energy storage into a wall

 

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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