blockLimits
Information
This block models the multi zone VAV AHU minimum outdoor air control with a single common damper for minimum outdoor air and economizer functions based on outdoor airflow measurement, designed in line with ASHRAE Guidline 36 (G36), PART 5.N.6.c.
The controller is enabled when the supply fan is proven on (uSupFan=true),
the AHU operation mode
Buildings.Obsolete.Controls.OBC.ASHRAE.G36_PR1.Types.OperationModes equals occupied,
and the freeze protection stage
Buildings.Obsolete.Controls.OBC.ASHRAE.G36_PR1.Types.FreezeProtectionStages is stage1 or lower.
Otherwise the damper position limits are set to their corresponding maximum and minimum physical or at
commissioning fixed limits. The state machine chart below illustrates listed conditions:
The controller sets the outdoor and return damper position limits so
that the outdoor airflow rate VOut_flow stays equal or above the
minimum outdoor air setpoint VOutMinSet_flow. The fraction of the controller
output signal between yMin and uRetDamMin is
linearly mapped to the outdoor air damper minimal position yOutDamPosMin
while the fraction of the controller output between uRetDamMin and
yMax is linearly mapped to the return air damper maximum position
yRetDamPosMax. Thus the dampers are not interlocked.
The following control charts show the input/output structure and an expected damper position limits for a well configured controller.
The expected damper position limits vs. the control loop signal are as follows:
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| Commissioning › Controller | |||
| Real | uRetDamMin | 0.5 | Loop signal value to start decreasing the maximum return air damper position |
| Controller | |||
| Buildings.Controls.OBC.CDL.Types.SimpleController | controllerType | Buildings.Controls.OBC.CDL.Types.SimpleController.PI | Type of controller |
| Real | k | 0.05 | Gain of damper limit controller |
| Real | Ti | 120 | Time constant of damper limit controller integrator block |
| Real | Td | 0.1 | Time constant of damper limit controller derivative block |
| Commissioning › Physical damper position limits | |||
| Real | retDamPhyPosMax | 1 | Physically fixed maximum position of the return air damper |
| Real | retDamPhyPosMin | 0 | Physically fixed minimum position of the return air damper |
| Real | outDamPhyPosMax | 1 | Physically fixed maximum position of the outdoor air damper |
| Real | outDamPhyPosMin | 0 | Physically fixed minimum position of the outdoor air damper |
Connectors
| Type | Name | Default | Description |
|---|---|---|---|
| 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.RealInput | VOutMinSet_flow_normalized | Effective minimum outdoor airflow setpoint, normalized by design minimum outdoor airflow rate | |
| Buildings.Controls.OBC.CDL.Interfaces.IntegerInput | uOpeMod | AHU operation mode status signal | |
| Buildings.Controls.OBC.CDL.Interfaces.IntegerInput | uFreProSta | Freeze protection status signal | |
| Buildings.Controls.OBC.CDL.Interfaces.BooleanInput | uSupFan | Supply fan status signal | |
| Buildings.Controls.OBC.CDL.Interfaces.RealOutput | yOutDamPosMin | Minimum outdoor air damper position limit | |
| Buildings.Controls.OBC.CDL.Interfaces.RealOutput | yOutDamPosMax | Maximum outdoor air damper position limit | |
| Buildings.Controls.OBC.CDL.Interfaces.RealOutput | yRetDamPosMin | Minimum return air damper position limit | |
| Buildings.Controls.OBC.CDL.Interfaces.RealOutput | yRetDamPosMax | Maximum return air damper position limit | |
| Buildings.Controls.OBC.CDL.Interfaces.RealOutput | yRetDamPhyPosMax | 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 | damLimCon | Damper position limit controller |
Revisions
-
July 10, 2020, by Antoine Gautier:
Changed default value of integral time for minimum outdoor air control. SetyMinto 0.
This is for #2019. -
March 14, 2020, by Jianjun Hu:
Replaced mulAnd by logic and block to avoid vector-valued calculation.
This is for #1829. -
July 17, 2017, by Michael Wetter:
Replaced block that checks for equality of real values within a tolerance by two inequality checks. -
June 06, 2017, by Milica Grahovac:
First implementation.