Fixed supply air temperature Airloop with dehumidification

asked 2023-09-04 13:03:21 -0500

clemcruv's avatar

updated 2023-09-06 11:34:09 -0500

Hi, I am trying to achieve dehumidification with my DOAS airloop on a singlezone. The control seems fine most of the year. But sometimes for no reason (not exceeding cooling coil capacity or reheat heating coil capacity) is not working. Are you aware of a dehumidification control issue? Or do you have any idea on why I am not able to reach my humidity setpoints? I am trying two different cases:

  • Zone dehumidification with humidstat setpoint at 55% image description

The yellow points are when there is occupation in my zone, otherwise there is no ventilation and so no deshumification. You can see that there are still many yellow points above the RH setpoint.
I set my min supply air temperature at 19° and max at 26°. I have correctly set setpointmanagers and humidistat for zone control.

Here are the resulting psychro charts, a case when it is not working and a case where it is working. If in one case, cooling my air from 25 to 2 (yet i don't understant why it so cold since in the sizing:system I set a design supply cooling temperature at 12°c) I don't understant why it can't cool more in the second cases where I get 60% HR in my zone instead of 55%.

image description image description

  • DOAS supply air dehumidification with humidity ratio setpoint at 9gwater/kgair

I get the same unmet setpoint results with dehumidification setpoint on the supply air.

image description

My airloop branch is the following:


z-7ik1vgwyt|air_loop,          ! Name
,                              ! Pressure Drop Curve Name
fan:systemmodel,               ! Component 1 Object Type
z-7ik1vgwyt|air_loop|fan_exhaust,    ! Component 1 Name
z-7ik1vgwyt|mechanical_ventilation|return|0,    ! Component 1 Inlet Node Name
z-7ik1vgwyt|mechanical_ventilation|return|1,    ! Component 1 Outlet Node Name
airloophvac:outdoorairsystem,  ! Component 2 Object Type
z-7ik1vgwyt|air_loop,          ! Component 2 Name
z-7ik1vgwyt|mechanical_ventilation|return|1,    ! Component 2 Inlet Node Name
z-7ik1vgwyt|mechanical_ventilation|supply|2,    ! Component 2 Outlet Node Name
coilsystem:cooling:dx,         ! Component 3 Object Type
z-7ik1vgwyt|air_loop|cta|cooling_coil,    ! Component 3 Name
z-7ik1vgwyt|mechanical_ventilation|supply|2,    ! Component 3 Inlet Node Name
z-7ik1vgwyt|mechanical_ventilation|supply|3,    ! Component 3 Outlet Node Name
coil:heating:electric,         ! Component 4 Object Type
z-7ik1vgwyt|air_loop|cta|heating_coil,    ! Component 4 Name
z-7ik1vgwyt|mechanical_ventilation|supply|3,    ! Component 4 Inlet Node Name
z-7ik1vgwyt|mechanical_ventilation|supply|4,    ! Component 4 Outlet Node Name
fan:systemmodel,               ! Component 5 Object Type
z-7ik1vgwyt|air_loop|fan_supply,    ! Component 5 Name
z-7ik1vgwyt|mechanical_ventilation|supply|4,    ! Component 5 Inlet Node Name
z-7ik1vgwyt|mechanical_ventilation|supply|5;    ! Component 5 Outlet Node Name



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