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[EnergyPlus_Support] Re: Humidity control in an Autosized AHU

To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Re: Humidity control in an Autosized AHU
From: "Elmer Morrissey" <elmofuddly@xxxxxxxxx>
Date: Tue, 18 Jul 2006 16:37:47 -0000
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Hello all, 

Can anyone help with this problem?

Kind regards

-Elmer

--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Elmer Morrissey"
<elmofuddly@...> wrote:
>
> Hi Mike and Richard,
> 
> I've uploaded the file. I made the changes you suggested but to no
> avail. It is called 	Hum Cont.idf 
> 
> I really appreciate your input
> 
> Kind regards
> 
> -Elmer
> 
> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Michael J. Witte"
> <mjwitte@> wrote:
> >
> > While it is true that EnergyPlus will not technically size for
> latent loads, it 
> > is possible to get fairly close by specifying different cooling
> supply air 
> > temperatures in the ZONE and SYSTEM SIZING objects.
> > 
> > In the ZONE SIZING object, the "Zone cooling design supply air
> temperature" is 
> > used to calculate the supply air volume flow rate to meet the peak
> sensible 
> > cooling load.  This temperature should be set to something like
12-14C. 
> > 
> > In the SYSTEM SIZING object, the airflow rate determined above will
> be used 
> > along with the "Central cooling design supply air temperature" to
> size the 
> > cooling coil.  The SYSTEM SIZING object below specified 5C as the
> "Central 
> > cooling design supply air temperature".  I presume this has been
> selected to be 
> > rather cool in order to provide adequate dehumidification with the
> assumption 
> > that reheat will prevent overcooling.  Note that the PLANT SIZING
> "Design loop 
> > exit temperature" must be at least 2 or 3 C cooler than this in
> order for the 
> > coil to provide this.  And the plant chilled water loop controls
> must be set 
> > this cold as well.
> > 
> > If this combination does not solve the high humidity control
> problem, please 
> > send the input file.
> > 
> > Mike
> > 
> > 
> > On 5 Jul 2006 at 10:26, Richard Raustad wrote:
> > 
> > > You will have to manually size the cooling coil to meet the latent
> load. 
> > > Sizing to meet the latent load is scheduled to be added to
EnergyPlus 
> > > for the next or following release.
> > > 
> > > Elmer Morrissey wrote:
> > > 
> > > > Hi Richard,
> > > >
> > > > I tried what you recommended and it seems I do have a capacity
> > > > problem. However I have used the following system sizing:
> > > >
> > > > SYSTEM SIZING,
> > > > A3:Loop, !- name of an AIR PRIMARY LOOP object
> > > > sensible, !- type of load to size on
> > > > autosize, !- Design (minimum) outside air
> > > > volumetric flow rate {m3/s}
> > > > 1, !- minimum system air flow ratio
> > > > 5, !- Preheat design set temperature {C}
> > > > 5, !- Central cooling design supply air
> > > > temperature {C}
> > > > 16, !- Central heating design supply air
> > > > temperature {C}
> > > > noncoincident, !- Sizing Option
> > > > Yes, !- Cooling 100% Outside Air
> > > > Yes, !- Heating 100% Outside Air
> > > > 0.0025, !- Central cooling design supply
> > > > air humidity ratio {kg-H2O/kg-air}
> > > > 0.008, !- Central heating design supply
> > > > air humidity ratio {kg-H2O/kg-air}
> > > > Design day, !- cooling design air flow method
> > > > , !- cooling design air flow rate {m3/s}
> > > > Design day, !- heating design air flow method
> > > > ; !- heating design air flow rate {m3/s}
> > > >
> > > > I can maintain around 55% RH during peak hours but I can't get
down
> > > > to 50%. The SYSTEM NODE SETPOINT TEMP after the cooling coil
becomes
> > > > as low as -55C during these hours. The `System Node Humidity Ratio
> > > > Max' displays similar swings in setpoint.
> > > >
> > > > During the winter, I able to maintain 50% RH most of the day but 4
> > > > of the hours display values around the 41% range for some unknown
> > > > reason. I checked things like infiltration and I can't seem to
> > > > account for it.
> > > >
> > > > I am using one central AHU for zone control. It supplies and
> > > > extracts air from the room. It contains a mixer, a CC, a HC, a
> > > > humidifier and a supply fan. Finally, it contains a terminal
reheat
> > > > coil.
> > > >
> > > > I appreciate your help.
> > > >
> > > > Kind regards
> > > >
> > > > -Elmer
> > > >
> > > > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx 
> > > > <mailto:EnergyPlus_Support%40yahoogroups.com>, Richard Raustad
> > > > <RRaustad@> wrote:
> > > > >
> > > > > Are you saying you don't have enough capacity to maintain RH, or
> > > > that
> > > > > the system is not actively controlling to the RH set point? I
> > > > assume you
> > > > > already have a humidistat in the control zone. What type of
system
> > > > are
> > > > > you using? If you are using a chilled water coil, the simple
> > > > > controller's control variable should be set to TEMPandHUMRAT
and a
> > > > > single zone max hum set point manager is required to place
the set
> > > > point
> > > > > at the cooling coil outlet node. Report out the temperature set
> > > > point
> > > > > after the cooling coil, when the RH rises above the set
point, the
> > > > > temperature set point should start to drop. The higher the
> > > > humidity
> > > > > rises above the set point, the lower the temperature set point
> > > > after the
> > > > > cooling coil. If this happens, the system is actively
controlling
> > > > to the
> > > > > RH set point and it is a capacity issue. If you are using DX
> > > > > System:AirLoop object, the Run on Latent Load field should
be set
> > > > to YES
> > > > > and the dehumidification control type field should be set to
> > > > COOLREHEAT.
> > > > > A single zone max hum set point manager is also required to
place
> > > > the
> > > > > humidity set point at the cooling coil outlet node. If you are
> > > > using a
> > > > > Furnace or Unitary System, all that is required is setting the
> > > > high
> > > > > humidity control field to YES in the furnace or unitary system
> > > > object.
> > > > >
> > > > > Elmer Morrissey wrote:
> > > > >
> > > > > > Hello all,
> > > > > >
> > > > > > I am having major difficulty maintaining 50% RH in a
single zone
> > > > > > supplied by a simple AHU.
> > > > > >
> > > > > > Fresh air- -> Fan -> CC -> HC -> Hum -> -----------TRH ->
> Zone->-
> > > > ----
> > > > > > ------exhaust
> > > > > >
> > > > > > The max humidity ratio is assigned after the cooling coil
while
> > > > the
> > > > > > minimum humidity ratio is set after the humidifier. I am
looking
> > > > at
> > > > > > a typical design day in a British climate and it should not be
> > > > > > overtaxing.
> > > > > >
> > > > > > Unfortunately, the RH is not maintained during the summer
months
> > > > > > (even though I oversized the system sizing object). The
average
> > > > RH
> > > > > > is around 57%. During the winter, RH values slip around
mid-day
> > > > for
> > > > > > a four hour period that I cannot explain.
> > > > > >
> > > > > > I've taken a look at the setpoint output from the CSV file for
> > > > the
> > > > > > max and min humidity ratios and it seems to me like they
> just are
> > > > > > not be applied within the model. I am aware that humidity
> > > > control is
> > > > > > not the strongest area in E+ but is there any way of
creating a
> > > > file
> > > > > > that would work for an autosized run?
> > > > > >
> > > > > > Can anyone help or point out some things I may have
overlooked?
> > > > > >
> > > > > > Kind regards
> > > > > >
> > > > > > -Elmer
> > > > > >
> > > > > >
> > > > >
> > > > >
> > > > > --
> > > > > Richard A. Raustad
> > > > > Senior Research Engineer
> > > > > Florida Solar Energy Center
> > > > > University of Central Florida
> > > > > 1679 Clearlake Road
> > > > > Cocoa, FL 32922-5703
> > > > > Phone: (321) 638-1454
> > > > > Fax: (321) 638-1439 or 1010
> > > > > Visit our web site at: http://www.fsec.ucf.edu
> <http://www.fsec.ucf.edu>
> > > > >
> > > > > UCF - From Promise to Prominence: Celebrating 40 Years
> > > > >
> > > > >
> > > > >
> > > > > [Non-text portions of this message have been removed]
> > > > >
> > > >
> > > >  
> > > 
> > > 
> > > -- 
> > > Richard A. Raustad
> > > Senior Research Engineer
> > > Florida Solar Energy Center
> > > University of Central Florida
> > > 1679 Clearlake Road
> > > Cocoa, FL  32922-5703
> > > Phone:   (321) 638-1454
> > > Fax:     (321) 638-1439 or 1010
> > > Visit our web site at: http://www.fsec.ucf.edu
> > > 
> > > UCF - From Promise to Prominence: Celebrating 40 Years
> > > 
> > > 
> > > 
> > > [Non-text portions of this message have been removed]
> > > 
> > > 
> > > 
> > > The primary EnergyPlus web site is found at:
> > > http://www.energyplus.gov
> > > 
> > > The group web site is:
> > > http://groups.yahoo.com/group/EnergyPlus_Support/
> > > 
> > > Attachments are not allowed -- please post any files to the
> appropriate folder
> > > in the Files area of the Support Web Site.
> > > 
> > > EnergyPlus Documentation is searchable.  Open EPlusMainMenu.idf
> and press the
> > > "search" button.
> > >  
> > > Yahoo! Groups Links
> > > 
> > > 
> > > 
> > >  
> > > 
> > > 
> > > 
> > > 
> > > 
> > 
> > 
> > ========================================================
> > Michael J. Witte, GARD Analytics, Inc.
> > EnergyPlus Testing and Support      
> > EnergyPlus-Support@
> >
>






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References:
- [EnergyPlus_Support] Re: Humidity control in an Autosized AHU
  - From: Elmer Morrissey

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