Relative humidity control using chilled water coils

asked 2020-05-18 11:56:09 -0500

Jim Dirkes gravatar image

updated 2020-05-18 15:54:53 -0500

I'm having difficulty making the zone relative humidity control properly with a chilled water system. I'll admit that I have a lot less experience with chilled water coils than with DX... Background:

  • The chiller is providing water at the correct setpoint temperature
  • Airflow is as specified
  • Zone temperature is at the proper setpoint
  • I tested 3 scenarios as shown below and hope that I've condesned the main details so you can comment without an IDF.

The short version of this question is this: Why is humidity NOT controlled (very well) with the simplest approach (:SingleZone:Humidity:Maximum)? That works very well for DX, so it's surprising and confusing (not to mention annoying) that chilled water coils don't work as well.

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Comments

You might want to review work on chilled water humidity control here

rraustad gravatar imagerraustad ( 2020-05-18 12:08:05 -0500 )edit

Do you have the coil's Controller:WaterCoil's Control Variable set to TemperatureAndHumidityRatio?

Eric Ringold gravatar imageEric Ringold ( 2020-05-18 12:34:39 -0500 )edit

Richard, I am not very versed in looking at GitHub issues, but it appears the the minimum plant iterations affect things adversely if the value was too low. I changed my model to 10 minimum with zero impact. Eric, Yes, I'm using the Temp&Humidity Ratio control variable.

Jim Dirkes gravatar imageJim Dirkes ( 2020-05-18 14:40:50 -0500 )edit

Then I would suggest reporting the coil outlet T and W and Tsetpoint and Wsetpoint and coil water flow rate (to see if water flow is maxing out) and then look at a point in time where RH is not controlled well.

rraustad gravatar imagerraustad ( 2020-05-18 15:39:24 -0500 )edit