Relative humidity control using chilled water coils

asked 2020-05-18 11:56:09 -0600

updated 2020-05-18 15:54:53 -0600

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.

image description

image description

image description

edit retag flag offensive close merge delete


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

rraustad gravatar image rraustad  ( 2020-05-18 12:08:05 -0600 )edit

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

Eric Ringold gravatar image Eric Ringold  ( 2020-05-18 12:34:39 -0600 )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 image Jim Dirkes  ( 2020-05-18 14:40:50 -0600 )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 image rraustad  ( 2020-05-18 15:39:24 -0600 )edit