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Re: [EnergyPlus_Support] Re: variable specific heat
Roberto:
There are multiple nodes developed within each layer based on some stability properties. E+ will handle the development of these nodes automatically. It will be difficult to determine how many nodes are within the PCM material layer. You can probably just watch the nodal temperature in the wall. If you plot this temperature at a given point of the year, you should see distinct sections that belong to each layer. If you output the Nodal temperature for ALL nodes of ALL walls, you will have a huge results file (probably too big to view in Excel). If you haven't already, I would only output the specific nodes you want to see; for example:
Report Variable,
Bedroom3Wall1 Nodal Temperature #1,
CondFD Nodal Temperature,
hourly;
Report Variable,
Bedroom3Wall1 Nodal Temperature #2,
CondFD Nodal Temperature,
hourly;
-------
Report Variable,
Bedroom3Wall1 Nodal Temperature #10,
CondFD Nodal Temperature,
hourly;
(I'm writing that from memory, so the format/syntax/keywords may be slightly off)
When you calculate the Cp from the enthalpy routine, make sure you don't use H/T directly. You will want to use DeltaH / DeltaT. Yes, you will want to use the H(T) data that you entered into E+. You entered H(T) for a certain range of Temperature. Make sure if you are outside of this range, that you use the constant Cp from the Material:Regular definition.
Edwin
----- Original Message ----
From: roblollini <r.lollini@xxxxxxxxxx>
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Sent: Wednesday, January 2, 2008 2:42:26 PM
Subject: [EnergyPlus_Support] Re: variable specific heat
Thank you very much for your answer. I would have two other
questions:
Why in the report there are always 10 nodes even if there are only 3
layers?
Do you mean calculate Cp of the PCM layer as a ratio: h(T)/T with h
(T) the enthalpy vs temperature function introduced
in "MaterialProperty: TemperatureDep: CondFD"? Which node I have to
consider?
Thank you again.
Roberto
--- In EnergyPlus_Support@ yahoogroups. com, Edwin Lee <leeed2001@. ..>
wrote:
>
> As far as I know, there is not a report variable for Cp in the
finite difference model. You can, however, report the nodal
temperatures, and from this, you can use your h vs. T data to
produce a Cp. I'm not completely sure why the Cp is not reported,
but if it were, there would be multiple Cp values for the layer (one
for each finite difference node within the PCM).
>
> Good luck,
> Edwin
>
> ----- Original Message ----
> From: roblollini <r.lollini@. ..>
> To: EnergyPlus_Support@ yahoogroups. com
> Sent: Wednesday, January 2, 2008 9:11:34 AM
> Subject: [EnergyPlus_ Support] variable specific heat
>
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> I am simulating a building with a PCM layer in the
external wall. I
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> would like to know if there was an EnergyPlus report for the
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> variable: "specific heat" or "thermal mass", calculated by condFD
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> algorithm. I need such values to define monthly average thermal
mass
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> of a construction that have to be input in a non-dynamic monthly
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> energy balance calculation.
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> Thank you very much for any suggestion.
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> Roberto
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