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RE: [EnergyPlus_Support] Simple Transient Model

To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: RE: [EnergyPlus_Support] Simple Transient Model
From: "Michael J. Witte" <mjwitte@xxxxxxxx>
Date: Fri, 08 Dec 2006 14:39:52 -0600
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Please post your file in the yahoo group files area or send zipped to 
energyplus-support@xxxxxxxx

Mike


On 6 Dec 2006 at 11:15, Elizabeth Ricker wrote:

> Brent,
>       I tried setting my h values very high, to 1000, as you suggested. This
> still gave me very strange results.  The only way that I have got results that
> even remotely match what I would expect are when I use hin = .1 and hout = 10.
> Any other suggestions as to why I might be having issues?  Perhaps it is
> something with the loads convergence that the program is not detecting an
> error for?  
>    
>   Thanks,
>   Betsy
> 
> "Griffith, Brent" <brent_griffith@xxxxxxxx> wrote:
>           Betsy
> 
> You say below you are using a rather low surface convection coefficient
> of 1.0 W/m2-K. The overall surface conductivity from air to air
> includes this coefficient and yours will introduce a lot of thermal
> resistance. It sounds like you want to use a much higher value -- like
> maybe 1000.0 W/m2-K 
> 
> ________________________________
> 
> From: EnergyPlus_Support@xxxxxxxxxxxxxxx
> [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Elizabeth
> Ricker
> Sent: Tuesday, December 05, 2006 7:37 PM
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> Subject: Re: [EnergyPlus_Support] Simple Transient Model
> 
> Mike,
> 
> I took a look at the files for the ASHREA documentation, but that did
> not solve my problem. The primary issue is that I am trying to examine
> the temperature response in a system with NO thermal mass (i.e. the
> walls, floor, and roof all have very low densities ~.0001 and Cp values
> ~.0001). The only thermal mass that should be present is in the air
> within the room. Given these conditions I should be seeing a response
> that is very fast in letting the air in the room cool from 26C to the
> outdoor temperature of 0C. What I am actually seeing is a response on
> the order of 35 hours for air to cool with all walls adiabatic except
> for a single conducting wall. I am currently setting my adiabatic walls
> by giving them very low conductivites. Is there an alternative way of
> defining adabatic walls with no thermal mass? Any ideas on why the
> response time would be so long? Are there any other forms of thermal
> mass other than the air that might be residual in the simulation and
> giving me longer time constants than expected? 
> 
> Thank you for your help,
> 
> Betsy
> 
> "Michael J. Witte" <mjwitte@xxxxxxxx <mailto:mjwitte%40gard.com> >
> wrote:
> It is hard to say what the problem may be. Did you zero out all of the
> solar 
> in the weather file, or set all of the surfaces to "NoSun"?
> 
> A similar test is reported in "EnergyPlus Testing with ASHRAE 1052-RP
> Toolkit - 
> Building Fabric Analytical Tests". Perhaps comparing your test inputs
> and 
> results with tests TC1-TC3 will help you find the problem. This report
> is 
> available at:
> 
> http://www.eere.energy.gov/buildings/energyplus/testing.html
> <http://www.eere.energy.gov/buildings/energyplus/testing.html> 
> 
> Follow the link for "ASHRAE Research Project 1052"
> 
> Mike
> 
> On 2 Dec 2006 at 17:49, elizabeth.ricker wrote:
> 
> > Hi All,
> > I am currently looking at a simple transient model in 
> > EnergyPlus. I would like to heat a room (1 zone) to 26C for a 
> > period, then allow it to cool to the outdoor temperature (0C) and 
> > analyze the time response of the system. I am looking at the 
> > reponse given that heat is only leaving through one wall, there is 
> > no thermal mass in that wall, and the remainder of the walls are 
> > super insulating. The convection coefficients on each wall are set 
> > to 1 W/m2K and the conductivity of the single conducting wall is 
> > very high (k = 1000, L = .1). Given these conditions the only 
> > thermal mass in my model should be that of the air in the room. 
> > Also, I am running a modified weather file with T = 26C for the 
> > first month, and then going to 0C for the remainder of the year. The 
> > results that I am showing are presenting a much longer time reponse 
> > than I would expect, and do not necessarily show an exponential time 
> > decay. Any suggestions on what might be going wrong in my model? 
> > 
> > Thank you,
> > 
> > Betsy Ricker
> > 
> > 
> > 
> > 
> > The primary EnergyPlus web site is found at:
> > http://www.energyplus.gov <http://www.energyplus.gov> 
> > 
> > The group web site is:
> > http://groups.yahoo.com/group/EnergyPlus_Support/
> <http://groups.yahoo.com/group/EnergyPlus_Support/> 
> > 
> > Attachments are not allowed -- please post any files to the
> appropriate folder
> > in the Files area of the Support Web Site.
> > 
> > EnergyPlus Documentation is searchable. Open EPlusMainMenu.idf and
> press the
> > "search" button.
> > 
> > Yahoo! Groups Links
> > 
> > 
> > 
> > 
> > 
> 
> ========================================================
> Michael J. Witte, GARD Analytics, Inc.
> EnergyPlus Testing and Support 
> EnergyPlus-Support@xxxxxxxx <mailto:EnergyPlus-Support%40gard.com> 
> 
> ---------------------------------
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> The group web site is:
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> 
> Attachments are not allowed -- please post any files to the appropriate folder
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> 
> EnergyPlus Documentation is searchable.  Open EPlusMainMenu.idf and press the
> "search" button.
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> Yahoo! Groups Links
> 
> 
> 
> 
> 






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References:
- RE: [EnergyPlus_Support] Simple Transient Model
  - From: Griffith, Brent
- RE: [EnergyPlus_Support] Simple Transient Model
  - From: Elizabeth Ricker

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