The data are interpolated along a piece-wise linear relationship, it is not a ?staircase? as you describe. Intermediate points that don?t change the linear function are superfluous, but here your (a) and (b) are totally different between 0 and 26C. In the case of (a) there is a gradual increase from 0 to 26C, but in case (b) all the increase occurs between 24 and 26C.
From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Niraj Poudel
Sent: Thursday, August 16, 2012 3:47 PM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Discrepancy in PCM Results
Dear all,
I have defined a PCM (26 degree melt, 230 KJ/Kg enthalpy) using the Enthalpy-Temp curve two different ways using the object Materialproperty:phase change and applied it to the interior face of the east wall.
a) Gypsum Board PCM:
Temp - 0
Enthalpy - 0
Temp-26
Enthalpy-230000
Temp-100
Enthalpy-230000
b) Gypsum Board PCM1
Temp-0
Enthalpy-0
Temp-20
Enthalpy-0
Temp-24
Enthalpy-0
Temp-26
Enthalpy-230000
Temp-28
Enthalpy-230000
Temp-30
Enthalpy-230000
Temp-40
Enthalpy-23000
Temp-100
Enthalpy-23000
As you can see both "hypothetical PCMs" melt at 26 degrees and have the same energy storage capability.But when I use PCM -a versus PCM-b for the same IDF file. I get two different results in heating and cooling energy loads? A long time ago I was told that the enthalpy stays the same until you define a different temp/enthalpy pair.
For instance, if you define:
Temp-0
enthalpy-0
it stays enthalpy-0 even at temp 25. until you add another temp enthalpy pair such as
Temp-26
Enthalpy-230000.
So my question is why am I getting two different results?
I would appreciate any insight regarding this issue.
Sincerely yours'
Niraj
--
Niraj Poudel, Architectural Engineer.
PhD student, PDBE Program.
Clemson University, Clemson, SC.
--Niraj Poudel, Architectural Engineer.PhD student, PDBE Program.Clemson University, Clemson, SC.
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