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Re: [EnergyPlus_Support] Venting Wall Cavities



Rich,

Good description!

Fred W

"Richard J. Liesen" wrote:

> >Note also that moisture transfer
> >estimates for this (or any) construction in EnergyPlus are not as
> >refined as those calculated by a program such as WUFI.  When the brick
> >is wet by rain and then the sun shines on it, there is a very strong
> >water vapor flow toward both the inside and outside.  Also probably
> >significant energy dissipation in evaporation.  EnergyPlus does not
> >calculate how wet the brick may get for this transfer process because
> >the necessary calculation detail would likely dramatically slow down a
> >calculation process for building energy use.  Just one on the
> >compromises of life until the next generation of PC's duplicate super
> >computer power for everyone.
>
> Hello,
> I wanted to update some folks on the current and the near future moisture
> capabilities of EnergyPlus.  The current capabilities of moisture modeling
> in EnergyPlus are first and foremost the moisture interactions inside the
> zone.  Using the EMPD model option in EnergyPlus will allow a user to have
> the interior surface of the wall element interact with moisture for
> adsorption/desorption ie. night venting.  Another current capability of
> EnergyPlus is the MTF or Moisture Transfer Function.  The MTF option will
> allow for a first order approximation of the linear material property
> moisture effects for both adsorption/desorption and transmission of
> moisture through the wall element.  The key words are "first order
> approximation" and "linear material properties" as the limitations for the
> evaporation-condensation theory.
>
> As Ned Lyon was pointing out there have been limitations when a user wanted
> to simulate a whole building due to execution time for these large
> problems.  Programs like WUFI and MOIST from NIST do a much more detailed
> analysis, but are usually limited to a wall element or a zone.
>
> In the next release there will be a couple of solution algorithms included
> which will use a Finite Difference solution technique.  This implementation
> will be classified as unsupported due to the fact that future development
> is necessary to make it robust enough for general usage.  It will be
> available for researchers and for stout-hearted users to look at who have
> an understanding of Finite Difference and the stability requirements
> necessary.  Not every wall element will run for the next release due to
> lack of stability and the solution technique.  But we are starting to
> bridge the gap to detailed high computation type of solution techniques.
>
> In the development of the newer solution techniques, my guess is proving
> out correctly that the MoistFD (Moisture Finite Difference) with non-linear
> properties runs faster or about the same as the MTF.  So for non-linear
> properties this appears to be the most appropriate implementation
> method.  Not only does it provide non-linear moisture properties for the
> simulation it does so with a quicker simulation time then the MTF
> solution.  It also provides the ability to look at Temp and Moisture
> profiles through the building surface.  As a by product the Conduction
> Finite Difference (CondFD) algorithms are a trivial addition.  Some timings
> are shown below for this implementation.
>
> Timings for a annual one zone model with 7 surfaces (including one ground
> connected surface) using an auto sized purchased air using the Chicago, IL
> weather file are:
>      CTF             30secs
>      CondFD      59secs
>      MoistFD     3min 27secs
>      MTF             7min 32secs
>
> Future time and effort in development will be necessary to make this more
> robust and a general solution technique option for all user.  At the same
> time we all hope as Ned does that computers continue growing faster and faster.
>
> Thanks
> Dr. Richard J. Liesen  Ph.D. M.E.
> Associate Director, Building Systems Laboratory
> Department of Mechanical and Industrial Engineering
> University of Illinois at Urbana-Champaign
> www.bso.uiuc.edu
> * * * * * * * * * * * * * * * * * * * * * * *
>
> The primary EnergyPlus web site is found at:
> http://www.energyplus.gov
>
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>
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>
>  -- please post any files to the appropriate folder in the Files are of the Support Web Site.
>
>
>
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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 not allowed -- please post any files to the appropriate folder in the Files are of the Support Web Site.




 -- please post any files to the appropriate folder in the Files are of the Support Web Site.




 

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