Improved AirflowNetwork Flow Linkage Controls

design/FY2021/NFP-AFN-Linkage-Control.md

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+# Improved AirflowNetwork Flow Linkage Controls #
+
+Jason DeGraw, Prateek Shrestha
+
+Oak Ridge National Laboratory
+
+Original Date: March 31, 2021
+
+## Justification for New Feature ##
+AirflowNetwork does not currently distinguish between a control factor and a multiplier for flow linkages. One input signal is allowed that is limited to [0,1],
+which precludes many use cases, including variable crack lengths, per area leakage elements, and multiple windows represented by a single path. Futhermore, it
+is no longer possible to modify the IDD to allow for other uses.
+
+## Overview ##
+A multiplier factor enables an independent control of the size of a flow linkage without having to adjust the flow characteristics of the linkage component(s).
+Once the user defines such a linkage characteristics, changing merely the multiplier in one location will enable the user to change the number of leakage path
+openings connecting different nodes and can make the model set-up task faster and easier for the user.
+
+## Approach ##
+Previous work has added the necessary parameters to the function signatures to allow separate control and multiplier inputs.
+
+* Add the necessary input fields 
+* Separate the usage of the two values internal to AirflowNetwork 
+* Add schedulability and EMS control (budget permitting) 
+* Create unit tests and documentation
+
+## Testing/Validation/Data Sources ##
+Unit tests will be implemented to ensure numerical values are calculated properly.
+
+## Input Output Reference Documentation
+Additions will be made to the Input Output Reference for the multiplier associated with the flow linkage.
+
+## Input Description ##
+The current distribution linkage object will be modified to include the multiplier, control, and control schedule fields:
+
+```
+AirflowNetwork:Distribution:Linkage,
+      \min-fields 4
+      \memo This object defines the connection between two nodes and a component.
+ A1 , \field Name
+      \required-field
+      \type alpha
+      \note Enter a unique name for this object.
+ A2 , \field Node 1 Name
+      \required-field
+      \type object-list
+      \object-list AirflowNetworkNodeAndZoneNames
+      \note Enter the name of zone or AirflowNetwork Node.
+ A3 , \field Node 2 Name
+      \required-field
+      \type object-list
+      \object-list AirflowNetworkNodeAndZoneNames
+      \note Enter the name of zone or AirflowNetwork Node.
+ A4 , \field Component Name
+      \required-field
+      \type object-list
+      \object-list AirflowNetworkComponentNames
+      \object-list FansCVandOnOffandVAV
+      \object-list AFNCoilNames
+      \object-list AFNHeatExchangerNames
+      \object-list AFNTerminalUnitNames
+      \note Enter the name of an AirflowNetwork component. A component is one of the
+      \note following AirflowNetwork:Distribution:Component objects: Leak, LeakageRatio,
+      \note Duct, ConstantVolumeFan, Coil, TerminalUnit, ConstantPressureDrop, or HeatExchanger.
+ A5 , \field Thermal Zone Name
+      \type object-list
+      \object-list ZoneNames
+      \note Only used if component = AirflowNetwork:Distribution:Component:Duct
+      \note The zone name is where AirflowNetwork:Distribution:Component:Duct is exposed.
+N1 ,  \field Multiplier
+      \type real
+      \note 
+N2 ,  \field Control Value
+      \type real
+      \note 
+A6 ;  \field Control Schedule Name
+      \type object-list
+      \object-list ScheduleNames
+```
+
+A new object will be added for multizone linkages:
+
+```
+AirflowNetwork:MultiZone:Linkage,
+      \min-fields 4
+      \memo This object defines the connection between two nodes and a component.
+ A1 , \field Name
+      \required-field
+      \type alpha
+      \note Enter a unique name for this object.
+ A2 , \field Node 1 Name
+      \required-field
+      \type object-list
+      \object-list AirflowNetworkNodeAndZoneNames
+      \note Enter the name of zone or AirflowNetwork Node.
+ A3 , \field Node 2 Name
+      \required-field
+      \type object-list
+      \object-list AirflowNetworkNodeAndZoneNames
+      \note Enter the name of zone or AirflowNetwork Node.
+ A2 , \field Surface Name
+      \required-field
+      \type object-list
+      \object-list SurfAndSubSurfNames
+      \note Enter the name of a heat transfer surface.
+ A3 , \field Leakage Component Name
+      \required-field
+      \type object-list
+      \object-list SurfaceAirflowLeakageNames
+      \note Enter the name of an Airflow Network leakage component. A leakage component is
+      \note one of the following AirflowNetwork:Multizone objects:
+      \note AirflowNetwork:MultiZone:Component:DetailedOpening,
+      \note AirflowNetwork:MultiZone:Component:SimpleOpening,
+      \note AirflowNetwork:MultiZone:Surface:Crack,
+      \note AirflowNetwork:MultiZone:Surface:EffectiveLeakageArea,
+      \note AirflowNetwork:MultiZone:Component:HorizontalOpening, or
+      \note AirflowNetwork:MultiZone:Component:ZoneExhaustFan.
+      \note When the zone exhaust fan name is entered, any surface control fields below A3 are
+      \note ignored when the zone exhaust fan turns on.
+N1 ,  \field Multiplier
+      \type real
+      \note 
+N2 ,  \field Control Value
+      \type real
+      \note 
+A4 ;  \field Control Schedule Name
+      \type object-list
+      \object-list ScheduleNames
+```
+
+The planned modifications do not include the `AirflowNetwork:MultiZone:Surface` object. It will continue to work as-is. The intrazonal links object may also need to be
+modified, this will be discussed with the development team.
+
+## Outputs Description ##
+No new output variables will be implemented with this work as existing variables are sufficient to gather relevant airflow information.
+
+## Engineering Reference ##
+N/A
+
+## Example File and Transition Changes ##
+Suitable example file will be generated. Since the multiplier will be incorporated within existing framework of flow linages, no transition rules are anticipated.
+
+## References ##
+N/A