[EnergyPlus_Support] Re: Indoor humidity

["donbshireyiii" <shirey@xxxxxxxxxxxx>]

Chaoqin:

I'm posting my response to the yahoogroups list so everyone
understands what we already found.......




You have defined SOLUTION ALGORITHM as EMPD, but you haven't defined
any MATERIALPROPERTY:MOISTURE:EMPD objects.

You need to add MATERIALPROPERTY:MOISTURE:EMPD objects for the
interior surface materials which are used in your CONSTRUCTIONS, which
are then referenced by Surface:HeatTransfer objects. Currently, you
must do this for all interior surfaces for your zones (except Window,
GlassDoor and TDD:Diffuser subsurfaces) for the EMPD solution to work
properly.  Look at the example file EMPDTermReheat.idf and the file
MoistureMaterials.idf (in  the DataSets folder) for
MaterialProperty:Moisture:EMPD properties for various materials.

Alternately, you can change to Solution Algorithm CTF. When I changed
to CTF, things looked much more reasonable.

We will add Error messages in the next release to trap for these
situations, and also give the user more flexibility in assigning EMPD
properties to only a portion of the interior heat transfer surfaces. 

--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Chaoqin Zhai
<chaoqinz@a...> wrote:
> Thanks for your reply. Actually I have no doubt about the little
latent 
> cooling load. What really confuses me is the supply air humidity and
indoor 
> humidity ratio. Why would the supply humidity ratio lower than the
indoor? 
> And it is continuously lower.
> 
> Thanks again,
> Chaoqin
> 
> --On Wednesday, October 27, 2004 4:24 PM +0000 donbshireyiii 
> <shirey@f...> wrote:
> 
> >
> > Depending on the inlet air conditions to the cooling coil, the
outdoor
> > temperature (seen by the air-cooled condenser), the air flow rate
> > across the cooling coil, and the cooling coil characterictics
(SHR,
> > capacity, etc.), you very well may be getting only sensible
cooling
> > from the coil.
> >
> > If the air entering the cooling coil is around 7 g/kg, that's
about
> > 30-35% RH at 27C.  The coil would likely provide mostly sensible
> > cooling with these entering air conditions (maybe 5-10% of the
total
> > capacity would be toward latent removal).
> >
> > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Chaoqin Zhai
> > <chaoqinz@a...> wrote:
> >> Yes, I checked the temperature as well. The indoor temperature is
> > around
> >> 23oC, which is my setpoint. The temperature of the air coming
from
> > the
> >> cooling coil is around 12 oC. There is sensible cooling on the
coil,
> > but
> >> very little latent cooling.
> >>
> >> Thanks,
> >> Chaoqin
> >>
> >> --On Wednesday, October 27, 2004 2:38 PM +0000 donbshireyiii
> >> <shirey@f...> wrote:
> >>
> >> >
> >> > Are you sure that the DX cooling coil is operating during the
time
> >> > when you are seeing these conditions?
> >> >
> >> > From what you describe, it seems like you are mixing about
40-50%
> >> > outdoor air with 50-60% return air from the zone, and this air
is
> >> > being supplied back to the zone (with the cooling coil OFF). 
Did
> > you
> >> > check the temperatures as well?
> >> >
> >> >
> >> > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "zhaicq98"
> > <chaoqinz@a...>
> >> > wrote:
> >> >>
> >> >> Hi,
> >> >>
> >> >> I have a unitary system with DX cooling coil to condition a
> >> > one-zone
> >> >> building. I output the supply air condition as well as the
indoor
> >> > and
> >> >> outdoor air condition and I found something strange. The
supply
> > air
> >> >> humidity ratio is around 7 g/kg dry air, but the indoor
humidity
> >> >> ratio is around 5 g/kg. At that period the outdoor humidity
ratio
> >> > is
> >> >> around 9-10 g/kg. I have some occupants inside the zone. I do
not
> >> >> have infiltration when the HVAC is working. It seems so
confusing
> >> > to
> >> >> me and I would greatly appreciate it if someone can give me
some
> >> >> hints on it.
> >> >>
> >> >> Thanks a lot!
> >> >





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