Can the AirFlowNetwork handle two AirLoops serving the same zone?

asked 2020-02-19 16:48:09 -0500

mldichter
2555 ●2 ●10

I am modeling some multifamily housing with a common attic and all ducts running through the attic. Each individual unit is served by its own heatpump, but there's a DOAS system with ERV that is common to all the units. So for every residence, there is one AirLoop that delivers hot or cold air, and for all the residences there is one AirLoop that delivers outdoor air running continuously.

I've started implementing one heatpump AirLoop and the DOAS AirLoop serving only one zone. I think I've set up the AirLoops and AFNs correctly but I'm getting an error.

   ** Severe  ** ValidateDistributionSystem: Primary Air Loop Node is not found in AIRFLOWNETWORK:DISTRIBUTION:NODE = AFN UNIT3 DOAS ZONE SPLITTER
   ** Severe  ** ValidateDistributionSystem: Primary Air Loop Node is not found in AIRFLOWNETWORK:DISTRIBUTION:NODE = AFN UNIT3 DOAS ZONE MIXER
   ** Severe  ** The AirLoopNum defined in both AIRFLOWNETWORK:DISTRIBUTION:NODE objects in AFN UNIT3 DOAS ZONE INLET ZONE NODE LINKAGE are not the same. Please make sure both nodes should be listed in the same AirLoop as a valid linkage.
   **   ~~~   ** AirLoop defined in AFN UNIT3_ZONE DOAS SUPPLY INLET is UNIT3 DOAS, and AirLoop defined in UNIT3_ZONE is SYS UNIT3_ZONE GROUP
   ** Severe  ** The AirLoopNum defined in both AIRFLOWNETWORK:DISTRIBUTION:NODE objects in AFN UNIT3 DOAS ZONE NODE ZONE RETURN LINKAGE are not the same. Please make sure both nodes should be listed in the same AirLoop as a valid linkage.
   **   ~~~   ** AirLoop defined in UNIT3_ZONE is SYS UNIT3_ZONE GROUP, and AirLoop defined in AFN UNIT3_ZONE DOAS RETURN AIR NODE is UNIT3 DOAS

My best guess, based on the nodes being referenced in the errors and the "AirLoopNum" variable, for the cause of the error is the heapump and DOAS Airloop nodes merging at the inlet and outlet of the zone in the ZoneHVAC:EquipmentConnections Nodelist inputs.

ZoneHVAC:EquipmentConnections,
    Unit3_Zone,              !- Zone Name
    Unit3_Zone Equipment,    !- Zone Conditioning Equipment List Name
    Unit3_Zone Air Inlet NodeList,  !- Zone Air Inlet Node or NodeList Name
    ,                        !- Zone Air Exhaust Node or NodeList Name
    Unit3_Zone Air Node,     !- Zone Air Node Name
    Unit3_Zone Return Air NodeList;  !- Zone Return Air Node or NodeList Name

NodeList,
    Unit3_Zone Air Inlet NodeList,  !- Name
    Unit3_Zone Inlet Node,   !- Node 1 Name
    Unit3_Zone DOAS Supply Inlet;  !- Node 2 Name

NodeList,
    Unit3_Zone Return Air NodeList,  !- Name
    Unit3_Zone Return Air Node,  !- Node 1 Name
    Unit3_Zone DOAS Return Air Node;  !- Node 2 Name

This made me question whether or not the AirFlowNetwork can handle more than one AirLoop serving the same zone. I'm not asking anyone to fix my model, just a yes or no if the AirFlowNetwork can handle what I'm trying to do. If yes, is there an example file demonstrating?

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answered 2020-02-28 11:55:18 -0500

mldichter
2555 ●2 ●10

The answer appears to be no. With no responses I did a little test by trying to add a ZoneHVAC:UnitHeater to the AirflowNetwork_Attic_Duct.idf example file. The ZoneHVAC:UnitHeater is made of a fan and heating coil. The nodes are a zone air inlet and exhaust node. Energyplus started complaining once I added the exhaust node to the ZoneHVAC:EquipmentConnections object. Looks like the AFN in energyplus can only handle a single inlet and outlet per zone.

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Can you use a single DOAS ERV Airloop and add a ZoneHVAC:PackagedTerminalHeatPump to each zone? The DOAS could be used for supply and exhaust. If you want to add a separate exhaust fan for electrical usage, you can zero out the exhaust energy from the DOAS and add a dummy exhaust fan to each zone that doesn't move any air but adds electrical usage.

sspielman ( 2020-03-02 12:33:04 -0500 )edit

@sspielman I don't think I can add any ZoneHVAC:* objects to condition a zone since the ZoneHVAC:* objects require the "Zone Air Exhaust Node or NodeList Name" field in the ZoneHVAC:EquipmentConnections for that zone, and adding a Zone Air Exhaust Node in the same zone as the DOAS causes an error.