Airflow node errors in VRF system

asked 2015-10-26 02:39:16 -0500

bbrannon4
1715 ●1 ●2 ●15

updated 2015-12-18 17:53:28 -0500

I'm trying to model a VRF system (exceptional calc from model generated in CBECC-Com) using the default objects. Form what I can see, there are only two: the system itself and the terminal units. It seems like the default settings are good for a test run, so I ran everything as it is, but set the control zone to one of the zones in each system and turned heat recovery on. The errors I'm getting from it are all about unassinged airflow nodes. For example:

** Severe  ** IP: IDF line~55232 Error detected in Object=ZONEHVAC:TERMINALUNIT:VARIABLEREFRIGERANTFLOW, name=VRF ZONE TERMINAL 8
**   ~~~   ** Field [Terminal Unit Air Inlet Node Name] is required but was blank
************* IDF Context for following error/warning message:
************* Note -- lines truncated at 300 characters, if necessary...
*************  55229 ZoneHVAC:TerminalUnit:VariableRefrigerantFlow,
************* indicated Name=VRF Zone Terminal 8
************* Only last 4 lines before error line shown.....
*************  55230   VRF Zone Terminal 8,     !- Zone Terminal Unit Name
*************  55231   Always On Discrete 1,    !- Terminal Unit Availability Schedule
*************  55232   ,                        !- Terminal Unit Air Inlet Node Name
*************  55233   ,                        !- Terminal Unit Air Outlet Node Name
** Severe  ** IP: IDF line~55233 Error detected in Object=ZONEHVAC:TERMINALUNIT:VARIABLEREFRIGERANTFLOW, name=VRF ZONE TERMINAL 8
**   ~~~   ** Field [Terminal Unit Air Outlet Node Name] is required but was blank
************* IDF Context for following error/warning message:
************* Note -- lines truncated at 300 characters, if necessary...
*************  55255 Fan:OnOff,
************* indicated Name=VRF Zone Terminal Fan 8
************* Only last 9 lines before error line shown.....
*************  55256   VRF Zone Terminal Fan 8, !- Name
*************  55257   Always On Discrete 15,   !- Availability Schedule Name
*************  55258   0.6,                     !- Fan Total Efficiency
*************  55259   300,                     !- Pressure Rise {Pa}
*************  55260   Autosize,                !- Maximum Flow Rate {m3/s}
*************  55261   0.8,                     !- Motor Efficiency
*************  55262   1,                       !- Motor In Airstream Fraction
*************  55263   VRF Zone Terminal 8 Heating Coil Outlet Node, !- Air Inlet Node Name
*************  55264   ,                        !- Air Outlet Node Name
** Severe  ** IP: IDF line~55264 Error detected in Object=FAN:ONOFF, name=VRF ZONE TERMINAL FAN 8
**   ~~~   ** Field [Air Outlet Node Name] is required but was blank
************* IDF Context for following error/warning message:
************* Note -- lines truncated at 300 characters, if necessary...
*************  55286 OutdoorAir:Mixer,
************* indicated Name=VRF Zone Terminal 8 OA Mixer
************* Only last 5 lines before error line shown.....
*************  55287   VRF Zone Terminal 8 OA Mixer,           !- Name
*************  55288   VRF Zone Terminal 8 Mixer Outlet Node,  !- Mixed Air Node Name
*************  55289   VRF Zone Terminal 8 Outdoor Air Node,  !- Outdoor Air Stream Node Name
*************  55290   VRF Zone Terminal 8 Relief Node Name,  !- Relief Air Stream Node Name
*************  55291   ;                                       !- Return Air Stream Node Name

But I'm not really sure where I'm supposed to set these nodes. It seems like something that OpenStudio would know by default because each system is assigned to a zone and this is purely zonal recirculation (DOAS defined elsewhere). Is there a place I'm missing to put the terminals on an air loop?

Thanks, Ben

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answered 2015-12-18 17:50:36 -0500

rraustad

13599 ●72 ●12 http://www.fsec.ucf.edu/

updated 2015-12-18 17:52:35 -0500

The part of the message that shows IP as part of the message means that the input is being processed by the Input Processor (IP). The IP checks for fields that are required, or that are outside specified limits.

If you look at the first few fields in the IDD file (Energy+.idd), you will see syntax that specifies how an input file should be organized. Notice that the 1st, 3rd, and 4th field shown here are required inputs. Long story short, in addition to specifying the control zone, other inputs also need to be specified to complete a simulation.

ZoneHVAC:TerminalUnit:VariableRefrigerantFlow,
    \memo Zone terminal unit with variable refrigerant flow (VRF) DX cooling and heating coil
    \memo (air-to-air heat pump). The VRF terminal units are served by an
    \memo AirConditioner:VariableRefrigerantFlow system.
    \min-fields 19
A1,  \field Zone Terminal Unit Name
    \required-field
    \type alpha
    \reference ZoneTerminalUnitNames
A2,  \field Terminal Unit Availability Schedule
    \type object-list
    \object-list ScheduleNames
    \note The unit is available the entire simulation if this field is left blank
    \note Schedule values of 0 denote the unit is off.
A3,  \field Terminal Unit Air Inlet Node Name
    \required-field
    \type node
    \note the inlet node to the terminal unit
A4,  \field Terminal Unit Air Outlet Node Name
    \required-field
    \type node
    \note the outlet node of the terminal unit

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Comments

@David Goldwasser or @macumber what other OpenStudio objects would be required to complete the zone node connections for ZoneHVAC equipment?

rraustad ( 2015-12-18 18:28:20 -0500 )edit

I think the necessary connections would be made when calling addToThermalZone. @Kyle Benne or @aparker would be the best to answer this.

macumber ( 2015-12-18 23:49:10 -0500 )edit

Yes this is something that OS should take care of for you, and yes at the API level addToThermalZone is the method that does that. How are you interacting with OS? If from the API, you need a call to that add to zone method. If from the UI, you need to make zone assignments in the VRF drag and drop interface.