RE: [EnergyPlus_Support] Discrepancy in PCM Results

If you plot the two curves, they looked quite different.

The 24° point is not in the first curve. Brent has pointed out that.

The falling off at 40 and 100 could be typing errors.

Dr. Li

To: EnergyPlus_Support@xxxxxxxxxxxxxxx
From: nirajpdl@xxxxxxxxx
Date: Thu, 16 Aug 2012 18:32:53 -0400
Subject: Re: [EnergyPlus_Support] Discrepancy in PCM Results

Dear Brent,

Thank you for clarifying this issue and for taking the time to look into this for me.

Sincerely yours'

Niraj

On Thu, Aug 16, 2012 at 6:10 PM, Griffith, Brent <brent.griffith@xxxxxxxx> wrote:

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.

__._,_.___

Primary EnergyPlus support is found at: http://energyplus.helpserve.com or send a message to energyplus-support@xxxxxxxx The primary EnergyPlus web site is found at: http://www.energyplus.gov The group web site is: http://groups.yahoo.com/group/EnergyPlus_Support/ Attachments are currently allowed but be mindful that not everyone has a high speed connection. Limit attachments to small files. EnergyPlus Documentation is searchable. Open EPlusMainMenu.pdf under the Documentation link and press the "search" button.

Your email settings: Individual Email|Traditional
Change settings via the Web (Yahoo! ID required)
Change settings via email: Switch delivery to Daily Digest | Switch to Fully Featured
Visit Your Group | Yahoo! Groups Terms of Use | Unsubscribe

__,_._,___