blockReliefFan
Sequence for control of relief fan in AHU
Information
Sequence for controling relief fan that is part of AHU. It is developed based on Section 5.16.9 of ASHRAE Guideline 36, May 2020, with the modification to accommodate the single relief fan control.
-
The relief fan shall be enabled when the AHU supply fan is proven ON
(
u1SupFan=true), and shall be disabled otherwise. -
Building static pressure (
dpBui) shall be time averaged with a sliding 5-minute window and 15 second sampling rate (to dampen fluctuations). The average value shall be that displayed and used for control. -
A P-only control loop maintains the building pressure at a set point (
dpBuiSet) of 12 Pa (0.05 in. of water) with an output ranging from 0% to 100%. The loop is disabled and output set to zero when the relief fan is disabled. -
Fan speed shall be equal to the PID signal but no less than the minimum speed.
- When relief system is enabled, and the control loop output is above 5%, open the motorized dampers to the relief fans; close the dampers when the loop output drops to 0% for 5 minutes.
-
When the control loop output is above minimum speed (
relFanSpe_min) plus 15% by 7 minutes, start the relief fan. -
When the control loop output is below minimum speed (
relFanSpe_min) by 5 minutes, shut off the relief fan.
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| Real | relFanSpe_min | 0.1 | Relief fan minimum speed |
| Real | dpBuiSet | 12 | Building static pressure difference relative to ambient (positive to pressurize the building) |
| Pressure controller | |||
| Real | k | 1 | Gain, normalized using dpBuiSet |
| Advanced | |||
| Real | hys | 0.005 | Hysteresis for checking the controller output value |
Connectors
| Type | Name | Default | Description |
|---|---|---|---|
| Buildings.Controls.OBC.CDL.Interfaces.RealInput | dpBui | Building static pressure difference, relative to ambient (positive if pressurized) | |
| Buildings.Controls.OBC.CDL.Interfaces.BooleanInput | u1SupFan | AHU supply fan proven on status | |
| Buildings.Controls.OBC.CDL.Interfaces.RealOutput | yDpBui | Building static pressure difference, relative to ambient (positive if pressurized) | |
| Buildings.Controls.OBC.CDL.Interfaces.RealOutput | yDam | Damper commanded position | |
| Buildings.Controls.OBC.CDL.Interfaces.RealOutput | yRelFan | Relief fan commanded speed | |
| Buildings.Controls.OBC.CDL.Interfaces.BooleanOutput | y1RelFan | Relief fan commanded on |
Components
| Type | Name | Default | Description |
|---|---|---|---|
| Buildings.Controls.OBC.CDL.Reals.MovingAverage | movMea | Average building static pressure measurement | |
| Buildings.Controls.OBC.CDL.Reals.Sources.Constant | dpBuiSetPoi | Building pressure setpoint | |
| Buildings.Controls.OBC.CDL.Reals.Divide | div1 | Normalized the control error | |
| Buildings.Controls.OBC.CDL.Reals.Sources.Constant | conOne | Constant one | |
| Buildings.Controls.OBC.CDL.Reals.PID | conP | Building static pressure controller | |
| Buildings.Controls.OBC.CDL.Reals.GreaterThreshold | greThr | Check if the controller output is greater than threshold | |
| Buildings.Controls.OBC.CDL.Reals.LessThreshold | lesThr | Check if the controller output is near zero | |
| Buildings.Controls.OBC.CDL.Logical.Timer | tim | Check if the controller output has been near zero for threshold time | |
| Buildings.Controls.OBC.CDL.Logical.And | and2 | Check if the controller output is greater than threshold and the relief system has been enabled | |
| Buildings.Controls.OBC.CDL.Logical.Latch | lat | Enable damper | |
| Buildings.Controls.OBC.CDL.Reals.GreaterThreshold | greThr2 | Check if the controller output is greater than minimum speed plus threshold | |
| Buildings.Controls.OBC.CDL.Logical.Timer | upTim | Check if the controller output has been greater than threshold for sufficient long time | |
| Buildings.Controls.OBC.CDL.Reals.LessThreshold | lesThr3 | Check if the controller output is less than minimum speed | |
| Buildings.Controls.OBC.CDL.Logical.Timer | dowTim | Check if the controller output has been less than threshold for sufficient long time | |
| Buildings.Controls.OBC.CDL.Logical.Latch | lat1 | Stage down lag fan | |
| Buildings.Controls.OBC.CDL.Logical.Or | relDam | Open relief damper | |
| Buildings.Controls.OBC.CDL.Logical.And | relFan | Turn on relief fan | |
| Buildings.Controls.OBC.CDL.Conversions.BooleanToReal | booToRea2 | Convert boolean to real | |
| Buildings.Controls.OBC.CDL.Reals.Multiply | pro1 | Relief fan speed | |
| Buildings.Controls.OBC.CDL.Conversions.BooleanToReal | booToRea1 | Convert boolean to real |
Revisions
-
March 5, 2024, by Michael Wetter:
Corrected wrong use ofdisplayUnit. -
September 20, 2022, by Jianjun Hu:
First implementation.