openstudio dehumidifying with humidistat shows no effect

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

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:

I created a scedule set to a constant value 60, with 'scedule type' set to 'percent'
I created a 'Setpoint Manager Single Zone Humidity Maximum' at the outlet node of the cooling coil
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

TaylorRoberts

2903 ●1 ●2 ●13 http://www.group14eng.com/

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 ( 2018-01-11 14:57:05 -0500 )edit

Maybe you need a cooling and heating setpoint schedule?

TaylorRoberts ( 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 ( 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.

ericringold ( 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.

InitController
if ( ( Node( SensedNode ).HumRatMax > 0 ) && ( Node( SensedNode ).HumRat > Node( SensedNode ).HumRatMax ) ) {

rraustad ( 2018-01-12 08:03:49 -0500 )edit

@Prinz Qwert For me it works Without cooling and heating setpoint schedule. Could you post your model?

Avi ( 2018-01-12 15:31:21 -0500 )edit

Hello everyone! Thank you for your answers. I still wasn't able to solve the problem. I uploaded ny model here: link

Prinz Qwert ( 2018-01-13 07:00:06 -0500 )edit

@Prinz Qwert I wasn't able to get the dehumidification work in your model. It is something to do with sizing of the system, but I don't know enough about that to solve it.

Avi ( 2018-01-13 14:00:24 -0500 )edit

You win, I've never seen a coil this large (22GW): Component Sizing Information, Coil:Cooling:Water, COIL COOLING WATER 1, Design Size Design Coil Load [W], 22175304673.2975

and operating at over 350,000,000 CFM.

The controller is working, except that the air flow is soooo large that the requested delta w needed to dehumidify is very small. However, I don't see a delta w across the water cooling coil. Not sure why.

rraustad ( 2018-01-13 15:31:10 -0500 )edit

Thank you for your help! I will try to fix the size of the cooling coil then!

Prinz Qwert ( 2018-01-16 07:46:19 -0500 )edit

This and the "link" described in the question taught me how to control humidity in my model which happens to be in Houston. Thank y'all!!!