[EnergyPlus_Support] Re: Maximum humidity control

["donbshireyiii" <shirey@xxxxxxxxxxxx>]

Sam:

I see a few problems with the input data file:

1)  You have 2 temperature setpoint managers trying to control the
cooling coil air outlet node: SET POINT MANAGER:SCHEDULED [Supply Air
Temp Manager] and SET POINT MANAGER:SINGLE ZONE REHEAT.  You should
eliminate the SET POINT MANAGER:SINGLE ZONE REHEAT.  The way you had
it configured, the set point temperature for air leaving the cooling
coil was initially set at 13C (in summer), and then the 2nd set point
manager was resetting it based on the sensible load in the zone being
controlled.  Assuming you want this to be an air-reheat system, you
should eliminate the Single Zone Reheat setpoint manager. The SINGLE
DUCT:CONST VOLUME:REHEAT air distribution unit that you have defined
will take care of the air reheating that you need.

2)  For high humidity control, you are currently telling SET POINT
MANAGER:SINGLE ZONE MAX HUM that the set point node is the air loop
outlet node (Air Loop Outlet Node).  You need to change this to be the
cooling coil outlet node (Cooling Coil Air Outlet Node).  When zone
humidity exceeds your setpoint of 52% RH, then this manager will reset
the cooling coil outlet air temperature setpoint to a lower value to
improve dehumidification.

3)  You might want to consider changing the coefficients for your
variable speed pumps.  Currently you have them at 1,0,0,0: this mean
the Rated Power is consumed regardless of PLR.  You might want to
consider using 0,1,0,0 so that pump power varies with PLR.

Once you make changes #1 and #2 above, the controls work properly but
the cooling coil isn't able to reduce the supply air temperature to
13C (or lower if high humidity is detected) for certain hours. You'll
need to look at the cooling plant and determine why this is happening.
Maybe the cooling coil, chiller, or cooling towers are undersized.

Also, is there a particular reason why you are specifying all PLANT
OPERATION SCHEMES with control scheme "Uncontrolled Loop Operation"?

Don


--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "donbshireyiii"
<shirey@f...> wrote:
> Sam:
> 
> I just ran the example file "5zoneWaterCooled_HighRHControl.idf"
with
> the latest version of EnergyPlus (1.2.2).
> 
> The relative humidity setpoint of 50% RH is maintained in SPACE2-1
> (which is the zone referenced by ZONE CONTROL:HUMIDISTAT) for the
> summer day simulation (July 7) during the daytime hours when the
> cooling system is scheduled to operate (except for the first hour
that
> the system is operating since the system is pulling down to the
> setpoint). Clearly the 50% RH setpoint will not be held during hours
> when the HVAC system is scheduled off.  If you want the example file
> to maintain humidity at the 50% RH setpoint during all hours of the
> day, then the cooling system schedules and setpoints need to be
> extended appropriately.
> 
> When the HVAC system is turned off, the RH level rises significantly
> for this example input file.  A quick look at the IDF shows that
high
> occupancy levels extend well past the time when the HVAC system is
> turned off at hour 17, which wouldn't normally happen. If you
realign
> the occupancy schedule with the HVAC operating schedules, then you
> don't see this large increase in indoor RH levels during overnight
> hours when the HVAC system is scheduled OFF.
> 
> I'll now look at the file you posted and see if I can help determine
> why you aren't able to maintain your high humidity setpoint.
> 
> Don
> 
> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Sam Roose <sam@e...>
wrote:
> > I have just uploaded a file to the support groups in Problem
> Submittals
> > under "Sam Roose" called "15_humid_control". In this case I am
> trying to get
> > minimum and maximum humidity setpoints going in the same file (the
> min.
> > setpoint being 45%, the max setpoint 59%) or at least get maximum
> humidity
> > working, which as yet I have not been able to do. Maximum humidity
> needs to
> > be controlled by the cooling coil.
> > 
> > The example file that looks closest to what I am after is
> > "5zoneWaterCooled_HighRHControl.idf". This supposedly contorls
> maximum
> > humidity to 50%, although the results for this file show that
> humidity is
> > still getting to 90%. My file is showing max humidity as 80%. I
have
> tried
> > taking the humidifier out, using TempHumrat as the control
variable
> on the
> > cooling coil and cranking up my cooling capacity - so far no luck.
> > 
> > So my questions are:
> > 
> > 1) Is there an example file with a plant loop and using a cooling
> coil to
> > dehumidify that successfully controls maximum humidity to a
certain
> > percentage?
> > 
> > 2) Is there a node out of place which is causing problems with
> controlling
> > maximum humidity in my file?
> > 
> > 3) Is it possible to create a maximum humidity deadband in
> EnergyPlus now or
> > in future?
> > 
> > My file runs in Version 1.2.1
> > 
> > Thanks in advance
> > 
> > Sam Roose




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