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Humidifier:Steam:Gas option "VariableInletWaterTemperature" not working (EnergyPlus)

asked 2024-04-10 04:03:13 -0500

PmP's avatar

updated 2024-04-10 14:22:22 -0500

Good day to anyone reading this post.

I am working with an HVAC system with humidification and when checking the input-output reference I saw that there is an option for the Gas-Fired humidifier to extract water from an storage tank. And this could be used for thermal storage which I'm interested in simulating.

The last variable of the input object "Humidifier:Steam:Gas" can be "FixedInletWaterTemperature" or "VariableInletWaterTemperature", defaulting to fixed. This variable is supposed to either do calculations with water always fixed at 20oC or do calculations with real water temperature.

However when using the "Variable" option and changing the temperature schedule of the storage tank the gas consumption of the humidifier is constant, therefore not seeing any difference regarding water temperature.

I have tried different temperature schedules for the storage tank as well as the mains, checked that the source code uses the exact string "VariableInletWaterTemperature" as an input for the last field of the humidifier object (If any other than that or fixed is inputted, the simulation stops anyways), I have changed from variable to fixed and it also doesn't change the consumption and I have checked the calculations of the source code "" and I can't see an easy to identify issue.

I tested this on the example file for the Humidifer:Gas so that I know the issue isn't in a different place. I use EP 9.4 but I also tested on the latest EP 24.1.0 ad the issue remains. Here is a dropbox link for the EP 9.4 version of the example files, one unchanged and one with the changes in the humidifier and addition of a water storage tank and temperature schedule.

The full text changes of the input files are from lines 2643 to 2685:

    Main Gas Humidifier,     !- Name
    ALWAYS_ON,               !- Availability Schedule Name
    autosize,                !- Rated Capacity {m3/s}
    autosize,                !- Rated Gas Use Rate {W}
    0.80,                    !- Thermal Efficiency {dimensionless}
    ThermalEfficiencyFPLR,   !- Thermal Efficiency Modifier Curve Name
    0,                       !- Rated Fan Power {W}
    0,                       !- Auxiliary Electric Power {W}
    Mixed Air Node 1,        !- Air Inlet Node Name
    Main Humidifier Outlet Node,  !- Air Outlet Node Name
    Tanque_Humidificador, !- Water Storage Tank Name

    Tanque_Humidificador,     !- Name
    ,                        !- Water Quality Subcategory
    1,                        !- Maximum Capacity {m3}
    0,                        !- Initial Volume {m3}
    0.5,                        !- Design In Flow Rate {m3/s}
    0.1,                        !- Design Out Flow Rate {m3/s}
    ,                        !- Overflow Destination
    Mains,                        !- Type of Supply Controlled by Float Valve
    0.25,                        !- Float Valve On Capacity {m3}
    1,                        !- Float Valve Off Capacity {m3}
    0.1,                        !- Backup Mains Capacity {m3}
    ,                        !- Other Tank Name
    ScheduledTemperature,                        !- Water Thermal Mode
    Domestic hot water setpoint temperature: Always 55.00  !- Water Temperature Schedule Name
     , !- Ambient Temperature Indicator
 , !- Ambient Temperature Schedule Name
 , !- Zone Name
 , !- Tank Surface Area {m2}
 , !- Tank U Value {W/m2-K}
 ; !- Tank Outside Surface Material Name

For the UNMET HOURS post, the last 6 fields of the storage tank are according to the guide unused and left for possible future ... (more)

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answered 2024-04-10 11:59:52 -0500

I ran your file and found that it's a bug in EnergyPlus. Indeed the Humidifier:Steam:Gas model will always use "FixedInletWaterTemperature" regardless of the input.

I have proposed a bugfix here. Unfortunately, there is no way for you to workaround the issue with the current EnergyPlus releases.

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Thank you for the answer and bugfix proposal. I wanted to use this issue as a starting point for trying to modify and rebuild the source code (for personal use only and at a really simple level) so the fix really helps as I was going to force it to always run the calculations for variable temperature.

PmP's avatar PmP  ( 2024-04-10 12:23:29 -0500 )edit

If you haven't seen it, there are good build instructions on the Wiki.

shorowit's avatar shorowit  ( 2024-04-10 12:32:05 -0500 )edit

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Asked: 2024-04-10 04:03:13 -0500

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Last updated: Apr 10