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Re: [EnergyPlus_Support] Tight RH control problem
1. Note that EnergyPlus autosizing is not generally sensitve to humidity
controls. The autosizing will not determine the minimum supply air temperature
required to meet humidity control requirements and size the cooling coil
accordingly. The cooling coil will be sized based on the total load seen at
the coil when supplying the cooling supply air temperature specified in the
SYSTEM SIZING object. You may have to do some trial and error or do a side
calculation to determine this value.
2. In the case of System Node Humidity Ratio Max, a value of zero indicates
the set point manager is not requesting any special dehumidification. The
controller treats zero as a special value and controls based on temperature
only.
3. There is no temperature setpoint on "AHU3 Fan Outlet Node". For the
controller to work with TEMPandHUMRAT, there must be both a humidity and
temperatur setpoint on the same node. Use SET POINT MANAGER:SCHEDULED or
WARMEST or SINGLE ZONE COOLING to place a temperature setpoint on this node.
Mike
On 15 May 2006 at 9:49, Elmer Morrissey wrote:
> 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
>
>
>
>
>
>
>
>
>
> The primary EnergyPlus web site is found at:
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>
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>
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>
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>
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>
>
>
>
>
>
>
>
========================================================
Michael J. Witte, GARD Analytics, Inc.
EnergyPlus Testing and Support
EnergyPlus-Support@xxxxxxxx
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