Re: [EnergyPlus_Support] Question About Modeling Moisture

["Michael J. Witte" <mjwitte@xxxxxxxx>]

The problem in this file is that moisture properties have been specified only
for some of the surfaces in the conditioned space.  The EMPD model is supposed
to accomodate this situation, but apparently it is not.  I added concrete
moisture properties for the slab floor and the summer conditioned space RH
(with Chicago weather) moves into the 40% range, peaking over 50%.  I would
recommend that you make sure there are moisture properties defined for the
inside material layer for all surfaces and sub-surfaces (except windows) which
are present in the conditioned zone.  A change request will be submitted to
investigate if partial specification of moisture properties should be allowed
and if so, if the model is handling this properly.

Mike


On 14 Apr 2005, at 13:12, bartlettbmw wrote:

>
>
> I am trying to model the effects of different HVAC system designs on
> indoor humidity levels in a residential home.  Using the CTF solver,
> the loads seem about right, but the indoor relative humidity varies
> much more than would be expected.  Looking into the EP
> documentation, it appears that there are two options, EPDM and MTF,
> availible to improve the model and more accurately account for
> moisture loads.  Since I am interested in running an annual
> simulation, the MTF solution probably will not work because the
> documentation warns of problems for annual simulations due to non-
> linearities in material properties with temperature.  This leaves
> the EPDM method.  Since the biggest moisture sink for the building
> will probably be the drywall, I imported the Gypsum EPDM properties
> from the included datasets.  When I run the simulation with these
> properties the results are given relative humidity values that are
> way too low (20% during the summer).  I tried adjusting the values
> for other materials with much lower moisture capacity, but the
> result is about the same.  I was wondering if anyone has used the
> EPDM model to achieve a resonable approximation to internal moisture
> loads, or if there is another way to model the loads that would be
> more accurate.
>
>
>
>
>
> 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 area of the Support Web Site.
>
> Yahoo! Groups Links
>
>
>
>
>
>
>
>
>



========================================================
Michael J. Witte, GARD Analytics, Inc.
EnergyPlus Testing and Support
EnergyPlus-Support@xxxxxxxx




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