blockSeparateWithAFMS
Outdoor air and return air damper position limits for units with separated minimum outdoor air damper and airflow measurement
Information
Block that outputs the position limits of the return and outdoor air damper for units with a separated minimum outdoor air damper and airflow measurement. It is implemented according to Section 5.16.5 of the ASHRAE Guideline 36, May 2020.
Minimum outdoor air set point
Calculate the outdoor air set point with Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.SetPoints.OutdoorAirFlow.
Minimum outdoor air control loop
Minimum outdoor air control loop is enabled when the supply fan is proven ON
(u1SupFan=true) and in occupied mode, and disabled and output set to
zero otherwise
The minimum outdoor airflow rate shall be maintained at the minimum outdoor air
set point by a reverse-acting control loop whose output is 0% to 100%.
From 0% to 50% loop output, the minimum outdoor air damper is opened from 0%
(minOutDamPhy_min) to 100% (minOutDamPhy_max).
Return air damper
- Return air damper minimum outdoor air control is enabled when the minimum outdoor air damper is fully open and the economizer outdoor air damper is less than a projected position limit, which is 5% when supply fan speed is at 100% design speed proportionally up to 80% when the fan is at minimum speed.
- Return air damper minimum outdoor air control is disabled when the minimum outdoor air damper is not fully open or the economizer outdoor air damper is 10% above the projected position limit as determined above.
-
When enabled, the maximum return air damper set point is reduced from 100%
(
retDamPhy_max) to 0% (retDamPhy_min) as the minimum outdoor air loop output rises from 50% to 100%.
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| Real | minSpe | Minimum supply fan speed | |
| Minimum OA control | |||
| Buildings.Controls.OBC.CDL.Types.SimpleController | minOAConTyp | Buildings.Controls.OBC.CDL.Types.SimpleController.PI | Type of minimum outdoor air controller |
| Real | kMinOA | 1 | Gain of controller |
| Real | TiMinOA | 0.5 | Time constant of integrator block |
| Real | TdMinOA | 0.1 | Time constant of derivative block |
| Commissioning › Physical damper position limits | |||
| Real | retDamPhy_max | 1 | Physically fixed maximum position of the return air damper |
| Real | retDamPhy_min | 0 | Physically fixed minimum position of the return air damper |
| Real | outDamPhy_max | 1 | Physically fixed maximum position of the outdoor air damper |
| Real | outDamPhy_min | 0 | Physically fixed minimum position of the outdoor air damper |
| Real | minOutDamPhy_max | 1 | Physically fixed maximum position of the minimum outdoor air damper |
| Real | minOutDamPhy_min | 0 | Physically fixed minimum position of the minimum outdoor air damper |
Connectors
| Type | Name | Default | Description |
|---|---|---|---|
| Buildings.Controls.OBC.CDL.Interfaces.RealInput | VOutMinSet_flow_normalized | Effective minimum outdoor airflow setpoint, normalized by design minimum outdoor airflow rate | |
| Buildings.Controls.OBC.CDL.Interfaces.RealInput | VOut_flow_normalized | Measured outdoor volumetric airflow rate, normalized by design minimum outdoor airflow rate | |
| Buildings.Controls.OBC.CDL.Interfaces.BooleanInput | u1SupFan | Supply fan proven on | |
| Buildings.Controls.OBC.CDL.Interfaces.IntegerInput | uOpeMod | AHU operation mode status signal | |
| Buildings.Controls.OBC.CDL.Interfaces.RealInput | uOutDam | Economizer outdoor air damper commanded position | |
| Buildings.Controls.OBC.CDL.Interfaces.RealInput | uSupFan | Commanded supply fan speed | |
| Buildings.Controls.OBC.CDL.Interfaces.RealOutput | yMinOutDam | Minimum outdoor air damper commanded position | |
| Buildings.Controls.OBC.CDL.Interfaces.BooleanOutput | yEnaMinOut | True: enable minimum outdoor air control loop | |
| Buildings.Controls.OBC.CDL.Interfaces.RealOutput | yOutDam_min | Physically minimum outdoor air damper position limit | |
| Buildings.Controls.OBC.CDL.Interfaces.RealOutput | yOutDam_max | Physically maximum outdoor air damper position limit | |
| Buildings.Controls.OBC.CDL.Interfaces.RealOutput | yRetDam_min | Minimum return air damper position limit | |
| Buildings.Controls.OBC.CDL.Interfaces.RealOutput | yRetDam_max | Maximum return air damper position limit | |
| Buildings.Controls.OBC.CDL.Interfaces.RealOutput | yRetDamPhy_max | Physical maximum return air damper position limit. Required as an input for the economizer enable disable sequence |
Components
| Type | Name | Default | Description |
|---|---|---|---|
| Buildings.Controls.OBC.CDL.Reals.PIDWithReset | conMinOA | Minimum outdoor air flow control |
Revisions
-
August 1, 2020, by Jianjun Hu:
First implementation.