Re: [EnergyPlus_Support] Condensation Problem

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

Comments from the radiant system expert . . .  Mike

It looks like this is really two separate issues--one regarding thermal 
mass and one regarding splitting zones.  With respect to the thermal mass 
addition, the best thing to do would be to have Zhen check his internal 
mass description (thickness and exposed area).  If the mass is too large, 
there is at least the potential for a variety of different effects, several of
which could conceivably cause a condensation problem.  Improper definition of
internal mass is something I've seen first-hand in another project and the
results can be somewhat strange.

As far as splitting things up goes, it sounds like in the second case the 
loads caused by outside conditions are concentrated into a smaller area 
with less tubing--the likely result if nothing is changed is that you will get
higher temperatures, how high depends on a lot of other variables.  In
counteracting that, Zhen increased the flow rate--but that is going to
ultimately drop the temperature of the slab which could then result in
condensation problems.  I'm not sure what he means by "it doesn't work"--does
that mean he gets more condensation warnings?  That would be logical from a
physical standpoint.

I don't know if this helps or not.  Condensation is a difficult thing to 
overcome in a radiant cooling system.  Sometimes, the condensation warning are
really telling the user that he needs to consider an alternative system.


On 31 Dec 2004, at 12:39, zhen tian wrote:

> 
> Hi, all:
> 
> I have a question during my simulation of combined
> radiant cooling and VAV system. I simulate a floor
> with 
> a core zone and 4 perimeter zones. Each perimeter zone
> has a perimeter office and a corridor between core
> zone and perimeter office.  The perimeter zone (office
> and corridor) is served by the same radiant slab
> cooling system and that is why I set it up as the same
> zone.
> 
> Everything is going well until I add internal mass
> into this perimeter zone, the condensation waring
> appeared. The interesting thing is that the simulated
> result of heating and cooling energy uses with
> internal mass increased.  Could somebody tell me what
> happened?
> 
> To test my simulation result, I compare the simulation
> result with measured temperatures.  For the measured
> office temperature in summer,with solar radiation, the
> mean radiant temperature vaires between 21 to 28C, and
> air temperature varies between 21 to 25.5C.  The
> corridor temperature constantly be kept at 22-23C.  As
> I set the office and corridor as one zone (each has
> the same area), the mean radian temperature is varied
> between 21 to 26.6 and air temperature varied 21 to
> 24.5C. Do you think this is reasonable as the mixed
> temperature for the whole zone? 
> 
> To get the different spaces temperatures according to
> the measured reslts, I tried to separate the office
> and corridor into 2 zones since there are big
> temperature differences between these two spaces
> (internal loads are separated into two zones, but
> outside solar gain is applied to the office, this is
> the real situation). But   this time the simulated
> mean radiant temperature of the office is much higher
> than measured (about 32C).  To decrease the MRT, I
> increase the chilled water flow (water temperature 16
> C) to the office zone, but this causes about 20
> condensation warnings appeared.  I increase the supply
> flow rate, but it does not work.  Could somebody tell
> me how to avoid these condensation warnings?
> 
> Thanks a lot.
> 
> Wish you all the best 2005.
> 
> Regards,
> 
> Zhen
> 
> 
> 
> 
> 
> 
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