[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [EnergyPlus_Support] Re: Humidity control in an Autosized AHU

To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] Re: Humidity control in an Autosized AHU
From: "Michael J. Witte" <mjwitte@xxxxxxxx>
Date: Wed, 05 Jul 2006 15:13:03 -0500
Comment: DomainKeys? See http://antispam.yahoo.com/domainkeys
Delivered-to: linda:lawrie.com@xxxxxxxxxxxxxxx
Delivered-to: mailing list EnergyPlus_Support@xxxxxxxxxxxxxxx
Domainkey-signature: a=rsa-sha1; q=dns; c=nofws; s=lima; d=yahoogroups.com; b=E79bzd8CKpQ2c5VQV3z3V6X1bQjkymKHVDIqnXPnLdpBGKjsrK4WLxWRBHDTZGeyR/njnYW2G2s4YjSXaBKi/E18BZYdv2qh8c5LzxZxNSbAcjUdm9W3fCuEDId8SG2G;
In-reply-to: <44ABCC11.2070507@fsec.ucf.edu>
List-id: <EnergyPlus_Support.yahoogroups.com>
List-unsubscribe: <mailto:EnergyPlus_Support-unsubscribe@yahoogroups.com>
Mailing-list: list EnergyPlus_Support@xxxxxxxxxxxxxxx; contact EnergyPlus_Support-owner@xxxxxxxxxxxxxxx
Organization: GARD Analytics
Priority: normal
References: <e8e4fb+lbr2@eGroups.com>
Reply-to: EnergyPlus_Support@xxxxxxxxxxxxxxx
Sender: EnergyPlus_Support@xxxxxxxxxxxxxxx

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@xxxxxxxx





------------------------ Yahoo! Groups Sponsor --------------------~--> 
See what's inside the new Yahoo! Groups email.
http://us.click.yahoo.com/2pRQfA/bOaOAA/yQLSAA/dkFolB/TM
--------------------------------------------------------------------~-> 

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

<*> To visit your group on the web, go to:
    http://groups.yahoo.com/group/EnergyPlus_Support/

<*> To unsubscribe from this group, send an email to:
    EnergyPlus_Support-unsubscribe@xxxxxxxxxxxxxxx

<*> Your use of Yahoo! Groups is subject to:
    http://docs.yahoo.com/info/terms/

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

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

Prev by Date: Re: [EnergyPlus_Support] Errors of autosizing the fan coil unit and the air-to-air heat pump at one time
Next by Date: [EnergyPlus_Support] Re: Lost Messages - convertESOMTR
Previous by thread: Re: [EnergyPlus_Support] Re: Humidity control in an Autosized AHU
Next by thread: [EnergyPlus_Support] Re: Humidity control in an Autosized AHU
Index(es):
- Date
- Thread