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