blockEnable
Information
This is a single zone VAV AHU economizer enable/disable sequence based on Section 5.18.7 and Section 5.1.17 of ASHRAE Guideline 36, May 2020. Additional conditions included in the sequence are:
- Buildings.Controls.OBC.ASHRAE.G36.Types.FreezeProtectionStages,
-
Supply fan status
u1SupFan, - Buildings.Controls.OBC.ASHRAE.G36.Types.ZoneStates.
The economizer is disabled whenever the outdoor air conditions
exceed the economizer high limit cutoff setpoint plus the hysteresis low limit parameter
(TOutHigLimCutLow or hOutHigLimCutLow) as shown in the figure.
And the economizer is enabled whenever the outdoor air conditions are below the economizer
high limit cutoff setpoint plus the hysteresis high limit parameter (TOutHigLimCutHig or
hOutHigLimCutHig). This sequence allows for all device types listed in
ASHRAE 90.1-2013 and Title 24-2013.
In addition, the economizer is disabled without a delay whenever any of the
following is true:
- supply fan is off,
-
zone state is
heating, -
freeze protection stage is not
0.
The following state machine chart illustrates the transitions between enabling and disabling:
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| Conditional | |||
| Boolean | use_enthalpy | true | Set to true to evaluate outdoor air (OA) enthalpy in addition to temperature |
| Advanced › Hysteresis | |||
| Real | delTOutHys | 1 | Delta between the temperature hysteresis high and low limit |
| Real | delEntHys | 1000 | Delta between the enthalpy hysteresis high and low limits |
| 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 |
Connectors
| Type | Name | Default | Description |
|---|---|---|---|
| Buildings.Controls.OBC.CDL.Interfaces.RealInput | TOut | Outdoor air temperature | |
| Buildings.Controls.OBC.CDL.Interfaces.RealInput | TCut | OA temperature high limit cutoff. For differential dry bulb temperature condition use return air temperature measurement | |
| Buildings.Controls.OBC.CDL.Interfaces.RealInput | hOut | Outdoor air enthalpy | |
| Buildings.Controls.OBC.CDL.Interfaces.RealInput | hCut | OA enthalpy high limit cutoff. For differential enthalpy use return air enthalpy measurement | |
| Buildings.Controls.OBC.CDL.Interfaces.BooleanInput | u1SupFan | Supply fan on/off status signal | |
| Buildings.Controls.OBC.CDL.Interfaces.IntegerInput | uFreProSta | Freeze protection stage status signal | |
| Buildings.Controls.OBC.CDL.Interfaces.IntegerInput | uZonSta | Zone state status signal | |
| Buildings.Controls.OBC.CDL.Interfaces.RealInput | uOutDam_max | Maximum outdoor air damper position, get from damper position limits sequence | |
| Buildings.Controls.OBC.CDL.Interfaces.RealInput | uOutDam_min | Minimum outdoor air damper position, get from damper position limits sequence | |
| Buildings.Controls.OBC.CDL.Interfaces.RealOutput | yOutDam_max | Maximum outdoor air damper position | |
| Buildings.Controls.OBC.CDL.Interfaces.RealOutput | yRetDam_max | Maximum return air damper position | |
| Buildings.Controls.OBC.CDL.Interfaces.RealOutput | yRetDam_min | Minimum return air damper position |
Components
| Type | Name | Default | Description |
|---|---|---|---|
| Buildings.Controls.OBC.CDL.Logical.And | andFrePro | Logical and that checks freeze protection stage | |
| Buildings.Controls.OBC.CDL.Logical.And | andEnaDis | Logical and that checks freeze protection stage and zone state | |
| Buildings.Controls.OBC.CDL.Logical.TrueFalseHold | truFalHol | 10 min on/off delay |
Revisions
-
August 29, 2023, by Hongxiang Fu:
Because of the removal ofLogical.And3based on ASHRAE 231P, replaced it with a stack of twoLogical.Andblocks. This is for #2465. -
August 1, 2020, by Jianjun Hu:
Updated according to ASHRAE G36, May 2020. -
July 30, 2019, by Kun Zhang:
Added the option to allow fixed plus differential dry bulb temperature cutoff. -
July 06, 2017, by Milica Grahovac:
First implementation.