blockSupplyFan
Block to control multi zone VAV AHU supply fan
Information
Supply fan control for a multi zone VAV AHU according to ASHRAE guideline G36, PART 5.N.1 (Supply fan control).
Supply fan start/stop
- Supply fan shall run when system is in the Cool-down, Setup, or Occupied mode
- If there are any VAV-reheat boxes on perimeter zones, supply fan shall also run when system is in Setback or Warmup mode;
- If the AHU does not serve dual duct boxes
that do not have hot-duct inlet airflow sensors (
have_duaDucBox=true) or the AHU does not have airflow measurement station (have_airFloMeaSta=false), sum the current airflow rate from the VAV boxes and output to a software point.
Static pressure setpoint reset
Static pressure setpoint shall be reset using trim-respond logic using following parameters as a starting point:
| Variable | Value | Definition |
|---|---|---|
| Device | AHU Supply Fan | Associated device |
| SP0 | iniSet | Initial setpoint |
| SPmin | minSet | Minimum setpoint |
| SPmax | maxSet | Maximum setpoint |
| Td | delTim | Delay timer |
| T | samplePeriod | Time step |
| I | numIgnReq | Number of ignored requests |
| R | uZonPreResReq | Number of requests |
| SPtrim | triAmo | Trim amount |
| SPres | resAmo | Respond amount |
| SPres_max | maxRes | Maximum response per time interval |
Static pressure control
Supply fan speed is controlled with a PI controller to maintain duct static pressure at setpoint
when the fan is proven on. The setpoint for the PI controller and the measured
duct static pressure are normalized with the maximum design static presssure
maxSet.
Where the zone groups served by the system are small,
provide multiple sets of gains that are used in the control loop as a function
of a load indicator (such as supply fan airflow rate, the area of the zone groups
that are occupied, etc.).
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| System configuration | |||
| Boolean | have_perZonRehBox | false | Check if there is any VAV-reheat boxes on perimeter zones |
| Boolean | have_duaDucBox | false | Check if the AHU serves dual duct boxes |
| Boolean | have_airFloMeaSta | false | Check if the AHU has AFMS (Airflow measurement station) |
| Trim and respond for pressure setpoint | |||
| Real | iniSet | 120 | Initial setpoint |
| Real | minSet | 25 | Minimum setpoint |
| Real | maxSet | Maximum setpoint | |
| Real | delTim | 600 | Delay time after which trim and respond is activated |
| Real | samplePeriod | 120 | Sample period |
| Integer | numIgnReq | 2 | Number of ignored requests |
| Real | triAmo | -12.0 | Trim amount |
| Real | resAmo | 15 | Respond amount (must be opposite in to triAmo) |
| Real | maxRes | 32 | Maximum response per time interval (same sign as resAmo) |
| Fan PID controller | |||
| Buildings.Controls.OBC.CDL.Types.SimpleController | controllerType | Buildings.Controls.OBC.CDL.Types.SimpleController.PI | Type of controller |
| Real | k | 0.1 | Gain of controller, normalized using maxSet |
| Real | Ti | 60 | Time constant of integrator block |
| Real | Td | 0.1 | Time constant of derivative block |
| Real | yFanMax | 1 | Maximum allowed fan speed |
| Real | yFanMin | 0.1 | Lowest allowed fan speed if fan is on |
Connectors
| Type | Name | Default | Description |
|---|---|---|---|
| Buildings.Controls.OBC.CDL.Interfaces.IntegerInput | uOpeMod | System operation mode | |
| Buildings.Controls.OBC.CDL.Interfaces.RealInput | ducStaPre | Measured duct static pressure | |
| Buildings.Controls.OBC.CDL.Interfaces.IntegerInput | uZonPreResReq | Zone static pressure reset requests | |
| Buildings.Controls.OBC.CDL.Interfaces.BooleanOutput | ySupFan | Supply fan on status | |
| Buildings.Controls.OBC.CDL.Interfaces.RealOutput | ySupFanSpe | Supply fan speed |
Components
| Type | Name | Default | Description |
|---|---|---|---|
| Buildings.Obsolete.Controls.OBC.ASHRAE.G36_PR1.Generic.SetPoints.TrimAndRespond | staPreSetRes | Static pressure setpoint reset using trim and respond logic | |
| Buildings.Controls.OBC.CDL.Reals.PIDWithReset | conSpe | Supply fan speed control |
Revisions
-
October 15, 2020, by Michael Wetter:
Moved normalization of control error to PID controller.
This is for #2182. -
March 12, 2020, by Jianjun Hu:
Removed the sum of flow rate as it is not used in any other sequences.
This is for issue 1829. -
January 7, 2020, by Michael Wetter:
Reformulated to avoid relying on thefinalkeyword.
This is for issue 1701. -
October 14, 2017, by Michael Wetter:
Added normalization of pressure set point and measurement as the measured quantity is a few hundred Pascal. -
August 15, 2017, by Jianjun Hu:
First implementation.