[EnergyPlus_Support] Tight RH control problem

["Elmer Morrissey" <elmofuddly@xxxxxxxxx>]

Hello all,

I would greatly appreciate any input with a system that requires 
tight RH control. I am having difficulty with an AHU which is 
comprised of 

Mixing box -> Coiling Coil -> Humidifier -> Fan ->-------------------
-reheat units -> zone

I am trying to undertake a simulation for an Art Gallery. 
Accordingly, I required tight RH control. At this stage in the 
simulation, I would like to fully autosize the system.

I need the AHU to control moisture ratios only (as the terminal 
reheat boxes will take care of temperature). Unfortunately, I am 
experiencing the cooling coil always being turned on along with the 
humidifier. Therefore, during the winter months, I have the cooling 
coil being turned on for no reason. 
	
The one thing I have noticed that the when I look at the `System 
Node Humidity Ratio Max' for the cooling coil's control node, the 
values are set to `0' during the winter months. I think this may be 
causing the cooling coil to attempt to strip 100% of the moisture 
from the air. I may be wrong, but I can't think of any other reason 
for this. Under normal circumstances, I would turn off the cooling 
coil in the winter months, however, due to the tight RH control, I 
need to keep it on for the year-round simulations.

I've uploaded the file (called 'Tight RH Control Problem') but I've 
also included the objects that may be of relevance. Once again, I 
would really appreciate people's input.

SET POINT MANAGER:SINGLE ZONE MIN HUM,
    zThirdCloseControl Min Hum Manager,  !- Name
    ,                        !- Control variable
    ,                        !- Schedule name
    AHU3 Humidifier Outlet Node,  !- Name of the set point Node or 
Node List
    zThirdCloseControl Node; !- Name of a Node List (or Node)


SET POINT MANAGER:SINGLE ZONE MAX HUM,
    zThirdMediaRoom Max Hum Manager,  !- Name
    ,                        !- Control variable
    ,                        !- Schedule name
    AHU3 CC Outlet Node,     !- Name of the set point Node or Node 
List
    zThirdCloseControl Node; !- Control zone air node name


CONTROLLER:SIMPLE,
    AHU3 Cooling Coil Controller,  !- Name
    TEMPandHUMRAT,           !- Control variable
    REVERSE,                 !- Action
    FLOW,                    !- Actuator variable
    AHU3 CC Outlet Node,     !- Control_Node
    AHU3 CC Water Inlet Node,!- Actuator_Node
    0.001,                   !- Controller Convergence Tolerance: 
delta temp from setpoint temp {deltaC}
    autosize,                !- Max Actuated Flow {m3/s}
    0;                       !- Min Actuated Flow {m3/s}

ZONE SIZING,
    zThirdMediaRoom,         !- Name of a zone
    18,                      !- Zone cooling design supply air 
temperature {C}
    28,                      !- Zone heating design supply air 
temperature {C}
    0.00777,                 !- Zone cooling design supply air 
humidity ratio {kg-H2O/kg-air}
    0.0083,                 !- Zone heating design supply air 
humidity ratio {kg-H2O/kg-air}
    flow/person,             !- outside air method
    0.00944,                 !- outside air flow per person {m3/s}
    ,                        !- outside air flow per zone {m3/s}
    1.2,                     !- zone sizing factor
    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}


SYSTEM SIZING,
    AHU3 Air Loop,           !- name of an AIR PRIMARY LOOP object
    total,                   !- type of load to size on
    autosize,                !- Design (minimum) outside air 
volumetric flow rate {m3/s}
    1,                       !- minimum system air flow ratio
    3,                       !- Preheat design set temperature {C}
    9,                       !- Central cooling design supply air 
temperature {C}
    16,                       !- Central heating design supply air 
temperature {C}
    noncoincident,           !- Sizing Option
    no,                      !- Cooling 100% Outside Air
    no,                      !- Heating 100% Outside Air
    0.00777,                 !- Central cooling design supply air 
humidity ratio {kg-H2O/kg-air}
    0.00783,                 !- 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}

Kind regards

-Elmer








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