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Re: [EnergyPlus_Support] RE: MTF: output variable meaning & few more doubts.

To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] RE: MTF: output variable meaning & few more doubts.
From: "Michael J. Witte" <mjwitte@xxxxxxxx>
Date: Tue, 15 Jul 2003 16:04:15 -0500
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EMPD models moisture storage and release, but not moisture transfer 
through the wall.

On 15 Jul 2003, at 16:30, habaza11@xxxxxx wrote:

> Mike;
> Does the EMPD account for materials moisture storage?. or it just
> calculates moisture transfer?. Thank you. Hussein Abaza  "Michael J.
> Witte" <mjwitte@xxxxxxxx> wrote:
> 
> >Miguel:
> >
> >The MTF algorithms are currently being reworked to deal with the
> >nonlinear property data to make it suitable for longer term
> >simulations.  Since the wall can store mositure, it is certainly
> >possible for moisture flux to be into the surface from both sides at
> >the same time.  One would expect this to stop at some point as the
> >material becomes saturated.  If you are unable to produce reasonable
> >results at this point, it may be best for you to use the EMPD model
> >until the MTF model is updated.
> >
> >Mike
> >
> >
> >On 3 Jul 2003, at 14:08, Miguel Angel Pascual wrote:
> >
> >> Thank you for your fast answer, but  I think that the variable
> >> "Layer Rel Humidity" should be expressed in % (per hundred instead
> >> of per one). The other relative humidity variables like
> >> "Environment:Outdoor Relative Humidity" and "Zone Air Relative
> >> Humidity" are expressed in units per hundred. This is not very
> >> important but as far as I know it isn't said anywhere in the
> >> manuals. But I have a few more doubts:
> >>
> >> - I have made several simulations under winter conditions, and I
> >> always get 0% relative humidity in Layer 2. The same problem occurs
> >> in "MTFTermReheat.idf" example under a winter design day (Dry Temp:
> >> 5ºC and Wet Temp: 3ºC). I think that this is not correct, but I
> >> don't know what am I doing wrong.
> >>
> >> - In my model I use a Unit Heater to maintain a 20ºC indoor
> >> constant temperature, but although there is no moisture source or
> >> sink, the humidity rate inside is lower than outside
> >> (Environment:Outdoor Humidity Ratio: 0.039 kgWater/kgAir and Zone
> >> Air Humidity Ratio: 0.034 kgWater/kgAir). I don't understand the
> >> reason for this difference. If I run this model with the CTF
> >> algorithm both variables are the same. Anyway, I was expecting a
> >> Zone Air Humidity Ratio about 0.043 kgWater/kgAir (inside air is
> >> coming from the outside through infiltration, so it should have the
> >> same humidity ratio increased by the difference in the air
> >> densities). The vapor pressures for this conditions will imply a
> >> moisture flux from the outside to the inside, so how is possible to
> >> have a moisture inside lower rate if moisture is coming from the
> >> outside through the wall?
> >>
> >> - About the "Outside/Inside Surface Mass Flux[kg/s/m2]" variables,
> >> I would like to know the meaning of the sign. I am also surprised
> >> about their magnitude. I am getting values around  -0.00015 kg/s/m2
> >> for the inside surface mass flux. I think it is a very big value,
> >> my wall is 30 m2: -0.00015 kg/s/m2 x 30 m2 x 3600 s/hour = 16.2 kgs
> >> of water per hour?!?!?!?!? You can get a similar value in the
> >> "MTFTermReheat.idf" example with a winter day.
> >>
> >>
> >> Thanks for your patience,
> >>
> >> Miguel Angel Pascual
> >>
> >>   -----Mensaje original-----
> >>   De: Richard J. Liesen [mailto:rliesen@xxxxxxxx]
> >>   Enviado el: miércoles, 02 de julio de 2003 15:34
> >>   Para: EnergyPlus_Support@xxxxxxxxxxxxxxx
> >>   Asunto: Re: [EnergyPlus_Support] MTF: output variable meaning
> >>
> >>
> >>
> >>   >Can anybody explain me the meaning of the output variables:   >
> >>   >- Layer Rel Humidity[]. Units?
> >>
> >>   This is the Relative Humidity inside the construction at each
> >> layer   interface.  Relative Humidity is explained in just about
> >> every   Thermodynamic text book, ASHRAE Handbook of fundamentals,
> >> and any   Psychrometric book.  It is unitless and runs normally
> >> between 0 and   1, where anything greater than 1.0 there would be
> >> condensation.   This value can be reported along with the humidity
> >> ratio to help the   user determine if   there was or could be
> >> condensation in the wall construction.
> >>
> >>
> >>   >- Outside Surface Mass Flux[kg/s/m2].
> >>
> >>   The Surface Mass Flux would be the amount [kg] of moisture that  
> >> would enter   or leave that material at the outside face.
> >>
> >>
> >>   Thanks Richard Liesen
> >>
> >>   >Thanks in advance,
> >>   >
> >>   >
> >>   >Miguel Ángel Pascual
> >>   >Dtor. Ingeniería
> >>   >MIYABI
> >>   >mapascual@xxxxxxxxxxxx
> >>   >948 203 644
> >>   >
> >>   >
> >>   >
> >>   >[Non-text portions of this message have been removed]
> >>   >
> >>   >
> >>   >
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- Re: [EnergyPlus_Support] RE: MTF: output variable meaning & few more doubts.
  - From: habaza11

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