"Node connections in branch are not consistent with object nodes" when modeling a ChillerHeater:Absorption:DirectFired

asked 2022-07-01 18:58:46 -0600

updated 2022-07-01 20:15:54 -0600

I'm attempting to model a ChillerHeater:Absorption:DirectFired and I get this error:

* Severe  * SimGasAbsorber: Invalid call to Gas Absorbtion Chiller-Heater GAHP
*   ~~~   * Node connections in branch are not consistent with object nodes.
*  Fatal  * Preceding conditions cause termination.
...Summary of Errors that led to program termination:
..... Reference severe error count=1
..... Last severe error=SimGasAbsorber: Invalid call to Gas Absorbtion Chiller-Heater GAHP

Here is my ChillerHeater:Absorption:DirectFired object:

ChillerHeater:Absorption:DirectFired,
  GAHP,               !- Name
  autosize,           !- Nominal Cooling Capacity {W}
  0.8,                !- Heating to Cooling Capacity Ratio
  0.97,               !- Fuel Input to Cooling Output Ratio
  1.25,               !- Fuel Input to Heating Output Ratio
  0.01,               !- Electric Input to Cooling Output Ratio
  ,                   !- Electric Input to Heating Output Ratio
  GAHP ChW Inlet,     !- Chilled Water Inlet Node Name
  GAHP ChW Outlet,    !- Chilled Water Outlet Node Name
  GAHP Cnd Inlet,     !- Condenser Inlet Node Name
  GAHP Cnd Outlet,    !- Condenser Outlet Node Name
  GAHP HW Inlet,      !- Hot Water Inlet Node Name
  GAHP HW Outlet,     !- Hot Water Outlet Node Name
  0.1,                !- Minimum Part Load Ratio
  1,                  !- Maximum Part Load Ratio
  1,                  !- Optimum Part Load Ratio
  29,                 !- Design Entering Condenser Water Temperature {C}
  7,                  !- Design Leaving Chilled Water Temperature {C}
  autosize,           !- Design Chilled Water Flow Rate {m3/s}
  autosize,           !- Design Condenser Water Flow Rate {m3/s}
  autosize,           !- Design Hot Water Flow Rate {m3/s}
  GasAbsFlatBiQuad,   !- Cooling Capacity Function of Temperature Curve Name
  GasAbsFlatBiQuad,   !- Fuel Input to Cooling Output Ratio Function of Temperature Curve Name
  GasAbsLinearQuad,   !- Fuel Input to Cooling Output Ratio Function of Part Load Ratio Curve Name
  GasAbsFlatBiQuad,   !- Electric Input to Cooling Output Ratio Function of Temperature Curve Name
  GasAbsFlatQuad,     !- Electric Input to Cooling Output Ratio Function of Part Load Ratio Curve Name
  GasAbsInvLinearQuad,!- Heating Capacity Function of Cooling Capacity Curve Name
  GasAbsLinearQuad,   !- Fuel Input to Heat Output Ratio During Heating Only Operation Curve Name
  EnteringCondenser,  !- Temperature Curve Input Variable
  AirCooled,          !- Condenser Type
  2,                 !- Chilled Water Temperature Lower Limit {C}
  ,                   !- Fuel Higher Heating Value {kJ/kg}
  NaturalGas,         !- Fuel Type
  1;                  !- Sizing Factor

I have double-checked all my nodes in other classes and they seem correct. Before I inserted the ChillerHeater, my model had an air-cooled chiller and 2 boilers and it ran fine. I have an SVG file for the prior model and some screenshots are below. In anticipation of replacing them, I named both the chiller and the first boiler "GAHP". The demand side is not shown for brevity, but the chilled water loop serves one dummy fan coil without any load. The heating hot water loop serves numerous heating hot water coils with load on them.

image description

In my current model that will not run due to the error, the ChillerHeater replaced the chiller and the first of two boilers. Please assist with any troubleshooting ideas. I'm using EnergyPlus 22.1.0 exclusively.

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answered 2022-07-04 11:29:45 -0600

Aaron Boranian

14155 ●83 ●24 http://bigladdersoftware.com/

It looks like your condenser inputs are incorrect. The condenser inlet node is used for BOTH air-cooled and water-cooled setups, but the condenser outlet node is ONLY required for water-cooled setups. You've set names for both condenser nodes, but near the end of your chiller heater object, it looks like you have set the condenser type input to "AirCooled".

If you want to keep an air-cooled setup, try leaving the condenser outlet node blank and make sure that the GAHP Cnd Inlet node is the name of an OutdoorAir:Node object (chiller heaters use outdoor air for condenser inlet).

If you instead want to use a water-cooled setup, change the condenser type to "WaterCooled" and make sure the condenser inlet/outlet nodes are on the demand side of a condenser loop.

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I get the same error after removing the condenser outlet node name and making sure the condenser inlet node name is the name of an OutdoorAir:Node object. Here is a link to an excerpt of my idf file including the pertinent objects from the relevant classes.

Bo White ( 2022-07-05 14:45:53 -0600 )edit

After some trial and error, I determined that the problem is on the heating side. If I remove "Boiler 2" and only have one pump in the hot water loop, then the error disappears. However, I consider this a partial solution because I would prefer to retain "Boiler 2" and its dedicated pump.

Bo White ( 2022-07-06 14:10:42 -0600 )edit

Hmmm... have you tried using a single hot water pump before the splitter and keeping the GAHP and "Boiler 2" on parallel branches after the splitter? "Boiler 2" wouldn't have a dedicated pump, but it would be part of the HVAC system. This is assuming that somehow the severe error is caused by having two separate pumps and not two separate water heating components.