Re: [EnergyPlus_Support] Space humidity fluctuation

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

Christian:

For your application, the MTF is best applied to the paper as 
internal mass and not the envelope.  The interior of the room would 
stay at much more constant temperature and humidity ratio conditions 
and thus extend the time that the material properties would be in 
range.  Be sure to read the section on Moisture Transfer Material 
Properties in the Engineering Document, starting on p. 23.

Also, remember that MTF models moisture transfer through the envelope 
as well as moisture capacitance.  This may explain why adding the 
envelope MTFs caused the conditions to change more rapidly.

Another option is to use the EMPD simulation on the internal mass and 
the building envelope.  The EMPD solution only models moisture 
capacitance, no moisture transfer through the envelope.

Regarding the results with MTF vs. CTF, remember that the absorption 
or release of moisture in the surfaces will alter the heat transfer 
at the surfaces.

Mike




On 7 Feb 2003, at 17:51, Christian Struck wrote:

> Linda,
> 
> many thanks for your quick reply to the simulation output! 
> 
> My question now is a of different nature. 
> I use the MTF algorithm to evaluate the influence of paper materials
> on the room humidity after plant failure. The space contains shelves
> filled with tons of paper. I used the internal mass facility to define
> the papers surface area and properties. I also applied MTF properties
> to the building fabric since I taught it is necessary to follow the
> MTF approach throughout the model.
> 
> When comparing results for a model with MTF properties applied to the
> paper only and a model with MTF properties applied to paper and
> building fabric I noticed the environment is more stable for the paper
> only option. Could you please advice whether it is necessary to apply
> MTF properties to the building fabric and I how does the MTF
> formulation treats the building fabric in case no MTF properties were
> applied. 
> 
> Another issue I noticed is, when comparing MTF and CTF results for the
> 24h plant failure the resulting mean air temperatures in the space
> decrease using CTF and increase using MTF independent on the external
> temperature. I do not have an explanation for that behaviour!  Please
> provide me with some keypoints I can use to get my understanding up to
> speed.
> 
> many thanks!
> 
> Christian
> 
> 
> 
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