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[EnergyPlus_Support] Re: Humidity control in an Autosized AHU
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, 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
>
> UCF - From Promise to Prominence: Celebrating 40 Years
>
>
>
> [Non-text portions of this message have been removed]
>
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