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Re: [EnergyPlus_Support] About the zone air relative humidity for a zone with windoow air conditioner



Also check to make sure that the ventilation is operating as desired. 
 There could be a problem with the control specifications on 
ventilation.

On 26 Jun 2003, at 8:30, Edward Lyon wrote:

> Relative humidity is temperature dependent.  If your zone temperature
> is higher than outside due to solar gains, there will be a depression
> in interior RH even though the moisture levels of interior and
> exterior air are the same.  Try looking at dew point temperatures to
> see if the interior is getting the outside moisture.  At 12 ACH with
> no AC the interior and exterior dew point temperatures should be
> essentially equal.  The DX AC window air conditioner can also give you
> some poor results for RH control also.  An over-sized unit that runs
> short cycles will typically dehumidify better in the model than a load
> matched system that runs full time.  In reality, the short cycle
> operation would produce almost no dehumidification.  Finally, if the
> moisture models do work properly, you may need to model several days
> to see the results you want.  In a recent test I performed we
> simulated occupancy moisture loads in two apartments, one with good
> ventilation and one with poor ventilation.  The data indicated that
> the poorly ventilated unit took about 3 days to "store up" moisture in
> the interior finishes before it reached a cyclical equilibrium with
> the induced load.  Since you can not be completely certain where the
> wall moisture storage starts after model warmup, you must run the
> simulation several days to reach your actual induced conditions,
> longer if you have high storage systems like masonry.  In fact, a
> precast concrete or concrete masonry unit wall system may take a year
> or more to equalize with its surroundings.  I'm not sure that the
> transfer function method implemented for moisture storage in
> EnergyPlus is as accurate for heavy weight construction as it could be
> for light weight stud wall systems which respond faster to ambient RH
> changes.  
> 
> Ned Lyon
> 
> Senior Staff Engineer
> Simpson Gumpertz & Heger Inc.
> 
> 41 Seyon Street
> Building #1, Suite 500
> Waltham, MA  02453
> 
> Phone:  781-907-9000
> Fax:  781-907-9009
> 
> 
> >>> zplin99@xxxxxxxxxxx 06/26/03 12:02AM >>>
> 
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