Cooling coil energy is very high even during a summer setback period

asked 2021-08-18 11:52:36 -0600

Biraj
77 ●1 ●5

updated 2022-02-18 16:59:48 -0600

__AmirRoth__

4446 ●5 ●17 http://bleedinggreenna...

Hi there,

I have a schedule for July and August setback at 85 deg F, however, the cooling coil energy is showing very high magnitude during that period. Can anyone help how I can find out what's trigerring the cooling coil ?

The system is package RTU with a electric heating coil.

I would appreciate any help.

https://estesmcclure01-my.sharepoint....

Thanks, Biraj

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Can you share the IDF?

bonnema ( 2021-08-21 15:27:31 -0600 )edit

Hi bonnema, I have uploaded the idf file here:

https://estesmcclure01-my.sharepoint....

Thank you

Biraj ( 2021-08-30 08:34:51 -0600 )edit

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answered 2021-08-30 08:50:36 -0600

rraustad

13814 ●79 ●12 http://www.fsec.ucf.edu/

The CoilSystem object is set point controlled. When a scheduled set point manager is used, the set point is not affected by the thermostat temperature. You could use a SetpointManager:SingleZone:Cooling object to control the coil where the thermostat would be used.

SetpointManager:Scheduled,
  Scheduled Deck Temp 121,                !- Name
  Temperature,                            !- Control Variable
  Deck Temperature,                       !- Schedule Name
  Node 1590;                              !- Setpoint Node or NodeList Name

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Thank you rraustad ! I changed the setpoint manager as you mentioned, but now I am getting few severe errors during the simulation. Can you please recommend/suggest any checks that I should do to avoid those errors of convergence ?

Error file: https://estesmcclure01-my.sharepoint....

Updated IDF file: https://estesmcclure01-my.sharepoint....

Appreciate your time and help !

Regards, Biraj

Biraj ( 2021-08-30 10:34:39 -0600 )edit

The low temperatures causing the severe warnings are usually caused in zones where the temperature is not maintained. I did not have Dallas weather so I used Phoenix and it ran through the year. I would check some zone temperatures to see if the thermostat set points are met. I see you are providing the coil sizes and those values may not be able to meet the load. Check all warnings in the err file and fix as many as you can. Also, you should upgrade to the latest version since bugs are fixed and if this is a bug could have already been corrected.

rraustad ( 2021-08-30 14:39:10 -0600 )edit

If you don't mind, could you please see if the model will run on dallas file ? I am still running issues on a different weather file.

[Here is the link:] (https://energyplus.net/weather-locati...)

Thank you very much !

Biraj ( 2021-08-30 17:05:09 -0600 )edit

Well, I did run using the Dallas weather and it stops with the same low temp warnings. I also notice you mix autosizing with hard sized coil inputs.

Autosize, !- Low Speed Gross Rated Total Cooling Capacity {W} 0.51914218752, !- Low Speed Rated Air Flow Rate {m3/s}

This results in a very low air flow per capacity (cfm/ton) and can lead to very cold coil outlet temps. Not sure if that is was is causing this error or not. Continued in next comment...

rraustad ( 2021-09-01 12:51:12 -0600 )edit

0.51914 / 4522.61121 = 1.14788E-4, oh, this flow ratio is too high for DX coils. I suggest autosizing all autosizable input.

Component Sizing Information, Coil:Cooling:DX:TwoSpeed, 2 SPD DX CLG COIL 121, User-Specified Low Speed Rated Air Flow Rate [m3/s], 0.51914
Component Sizing Information, Coil:Cooling:DX:TwoSpeed, 2 SPD DX CLG COIL 121, Design Size Low Speed Gross Rated Total Cooling Capacity [W], 4522.61121

rraustad ( 2021-09-01 12:52:38 -0600 )edit

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Cooling coil energy is very high even during a summer setback period

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Cooling coil energy is very high even during a summer setback period