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Re: [EnergyPlus_Support] Problems in maintaining humidity control
In addition, a supply air temperature set point of 17.5 C in summer may
not be adequate for a large dehumidification load in the zone. Check the
supply air outlet temperature and compare it with your summer supply air
set point temperature of 17.5 (as if you had no humidistat that changes
the set point). Is it well below this value, my guess is it is not. A
zone temperature/humidity set point of 21C/50% will require a supply air
outlet temperature no greater than 10C during times when humidity is
above the set point. If the temperature is below 10C, your CW coil does
not have enough latent capacity (moisture removal ability) to properly
dehumidify. You may need to reduce the chilled water temperature set
point to properly dehumidify the space (currently set at 6C but the
supply air temperature will be higher than this value) or increase the
size of the CW coil to provide more latent capacity. The low supply air
temperature set point indicates that a very large dehumidification load
is present, your current HVAC system is unable to handle this load.
Michael J. Witte wrote:
> When using humidity control on the central chilled water coil, the
> controller
> changes the chilled water setpoint to provide the required humidity ratio
> needed to meet the humidistat setpoint. The varying setpoint values
> reflect
> the adjusted setpoints for humidity control. Given the low numbers
> being seen,
> it appears that the airflow rates are not adequate to meet the
> humidity loads?
>
> Mike
>
>
> On 18 Feb 2005, at 8:25, Elmer Morrissey wrote:
>
> >
> >
> > Hello all,
> >
> >
> >
> > I am wondering if anyone has any experience in modelling VAV systems
> that
> > maintain strict control over temperature AND humidity in a zone.
> >
> >
> >
> > I am modelling an AHU that provides air to two interior zones in an
> art gallery.
> > I cannot seem to force the system to maintain control over the zones
> over a 24hr
> > period as required by the Art Gallery.
> >
> >
> >
> > One of my major problems that I have found is a floating setpoint on
> my VAV
> > system outlet node. During the winter, the setpoint output on the
> csv emulates
> > the idf input, however during the summer design day, the csv output
> for the
> > setpoint value floats from -57oC to 3oC. I cannot seem to locate the
> source of
> > this error as I have no errors or warning. It is scheduled to a set
> value of
> > 17.5oC during the summer and 16oC during the winter. I also have trouble
> > stipulating the flow using the sizing objects, they seem to be
> ignored but I am
> > guess this is due to an error elsewhere in the idf.
> >
> >
> >
> > I have uploaded the file to the yahoo page...
> AHU3_AirLoop_PurchasedPlant_V1.idf
> >
> >
> >
> > I would appreciate anyone's experience or advice with this matter.
> >
> >
> >
> > Kind regards
> >
> >
> >
> > -Elmer Morrissey
> >
> >
> > PhD Researcher, IRUSE, NUIC, Ireland.
> >
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--
Richard A. Raustad
Senior Research Engineer
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University of Central Florida
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