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openstudio dehumidifying with humidistat shows no effect

asked 2018-01-11 14:13:23 -0500

Prinz Qwert gravatar image

Hello everyone! I am trying to make an HVAC system that keeps a relative humidity at 60%. The building is in a very humid climate therefore I need dehumidifying. I tried to proceed as described in link However when I simulate it, the humidity is still at 90-100%

I proceeded like this:

  1. I created a scedule set to a constant value 60, with 'scedule type' set to 'percent'
  2. I created a 'Setpoint Manager Single Zone Humidity Maximum' at the outlet node of the cooling coil
  3. I set the control variable in the cooling coil to 'Temperature and Humidity Ratio'

What am I doing wrong?

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answered 2018-01-11 14:27:36 -0500

For the humidity control to work, you need to set the actuator node name to the inlet water node to the chilled water coil.

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Thank you for your answer, I set the actuater node nome to the inlet node, but it still doesn't work...

Prinz Qwert gravatar imagePrinz Qwert ( 2018-01-11 14:57:05 -0500 )edit

Maybe you need a cooling and heating setpoint schedule?

TaylorRoberts gravatar imageTaylorRoberts ( 2018-01-11 15:00:06 -0500 )edit

When the zone RH> 60%, is the cooling coil water flow rate already maxed out? If so, there will be no additional dehumidification available. Are you autosizing the coil capacity? If so, the coil size is based on the zone sensible load, not the additional latent load (i.e., total load). What HVAC system type are you using? Is that model able to dehumidify?

rraustad gravatar imagerraustad ( 2018-01-11 15:44:42 -0500 )edit

Doesn't the air system require a sensible load from the zone in order to operate, @rraustad? In which case cooling and heating setpoint schedules would be required, as @TaylorRoberts said.

Eric Ringold gravatar imageEric Ringold ( 2018-01-11 15:58:08 -0500 )edit

The water coil controller should turn the coil on if humrat > SP node humrat max. I would report the coil control node humrat and humratmax set point to see what's happening.

if ( ( Node( SensedNode ).HumRatMax > 0 ) && ( Node( SensedNode ).HumRat > Node( SensedNode ).HumRatMax ) ) {
rraustad gravatar imagerraustad ( 2018-01-12 08:03:49 -0500 )edit

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Asked: 2018-01-11 14:13:23 -0500

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Last updated: Jan 11