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