Output Variable for Coil Inlet Air Temperature in EnergyPlus Refrigeration Systems (AirChiller)

asked 2024-12-11 04:07:30 -0600

922 ●7 ●8

updated 2024-12-11 06:33:48 -0600

Hello everyone,

I am working on modeling a refrigeration system in EnergyPlus, specifically focusing on air chillers. According to the European Standard rating system, the actual cooling capacity of the air chiller is defined as a function of the dry-bulb air temperature entering the coil (Tcoil,inlet) and the average refrigerant evaporating temperature (Tevap). The formula for the total cooling capacity is as follows:

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where image description

My question is: Does EnergyPlus provide an output variable for the dry-bulb air temperature entering the coil (Tcoil,inlet)?

Thank you for your insights!

IDF file : https://drive.google.com/IDF_File

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answered 2024-12-11 06:05:25 -0600

Denis Bourgeois
2981 ●111 ●8 http://www.rd2.ca

updated 2024-12-11 07:46:45 -0600

Not a definitive answer - too long for a comment.

@Zakaria, I had initially posted a generic answer on how to output coil air inlet node temperatures (see below). But refrigeration systems are a bit different. For instance, based on the system described here, a ZoneHVAC:RefrigerationChillerSet's air inlet node name is unused:

Not used, reserved for future use. Current version exchanges energy directly with the zone, external of any air system.

This boils down to the zone air node. Check the .rdd file for related output variables. Hope this helps.

Initial, generic solution for coils. Coils have both inlet and outlet air nodes.

check the .rdd file for Output:Variable,*,System Node Temperature,hourly; !- HVAC Average [C]
replace the * with the coil "Field: Air Inlet Node Name"
change the reporting frequency if needed, e.g. "Timestep"

EDIT: Follow-up based on shared IDF. The AirChiller.idf file has the following entry:

Output:Variable,
    NODE_4,                  !- Key Value
    System Node Temp,        !- Variable Name
    Timestep;                !- Reporting Frequency

The .err file reports an issue with this. It should be System Node Temperature:

Output:Variable,
    NODE_4,                  !- Key Value
    System Node Temperature, !- Variable Name
    Timestep;                !- Reporting Frequency

Once fixed, the .eso files tracks the requested node temperature. I then replaced NODE_4 with *. There are only 5 node temperature time series being tracked (from the .eso file):

7,1,ZN,Zone Outdoor Air Drybulb Temperature [C] !TimeStep
195,1,ZN,Zone Air Temperature [C] !TimeStep
307,1,NODE_4,System Node Temperature [C] !TimeStep
308,1,NODE_5,System Node Temperature [C] !TimeStep
309,1,CONDENSER OUTDOOR AIR NODE,System Node Temperature [C] !TimeStep

Spot checked a dozen periods over the year:

variables 7 & 309 always match (expected)
variables 195, 307 & 308 always match (expected)

... e.g.:

2,1, 8,10, 0,13,50.00,51.00,Thursday
7,31.445974999562816
195,-18.17873918169955
307,-18.17873918169955
308,-18.17874294489641
309,31.445

I have to defer to more knowledge people when it comes to refrigeration units, but I suspect (from what I'm reading) that one cannot isolate coil air inlet vs outlet temperatures. Good news:

can output time series of all node temperatures
space is refrigerated at a constant -18.18 C all year.

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Comments

@Denis Bourgeois, thank you for your Not a definitive answer - too long for a comment.

In my case, the Air Inlet Node is not defined in the ZoneHVAC:EquipmentConnections object. My model may have been defined incorrectly.

I have attached the IDF file to provide more context and would greatly appreciate your insights.

https://drive.google.com/drive/IDF_File

Zakaria ( 2024-12-11 06:42:35 -0600 )edit

ZoneHVAC:EquipmentConnections,

    ZN,                      !- Zone Name

    Walk-in HVAC Equipment,  !- Zone Conditioning Equipment List Name

    ,                        !- Zone Air Inlet Node or NodeList Name

    ,                        !- Zone Air Exhaust Node or NodeList Name

    NODE_4,                  !- Zone Air Node Name

    NODE_5;                  !- Zone Return Air Node or NodeList Name

Zakaria ( 2024-12-11 06:45:48 -0600 )edit

@Zakaria, I edited my initial answer. The NODE_4 output variable request needed fixing.