blockReliefs
Information
This is a multi zone VAV AHU economizer modulation block. It calculates the outdoor and return air damper positions based on the supply air temperature control loop signal. It is implemented according to Section 5.16.2.3.d, Figure 5.16.2.3-1 of ASHRAE Guideline 36, May 2020. Damper positions are linearly mapped to the supply air control loop signal.
When the economizer is enabled, the PI controller modulates the damper positions. Return and outdoor damper are not interlocked. When the economizer is disabled, the damper positions are set to the minimum outdoor air damper position limits.
The control charts below show the input-output structure and an economizer damper modulation sequence assuming a well configured controller. Control diagram:
Multi zone AHU economizer modulation control chart:
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| Commissioning › Controller | |||
| Real | uMin | -0.25 | Lower limit of controller input when outdoor damper opens (see diagram) |
| Real | uMax | +0.25 | Upper limit of controller input when return damper is closed (see diagram) |
| Real | uOutDamMax | (uMin + uMax)/2 | Maximum loop signal for the OA damper to be fully open |
| Real | uRetDamMin | (uMin + uMax)/2 | Minimum loop signal for the RA damper to be fully open |
Connectors
| Type | Name | Default | Description |
|---|---|---|---|
| Buildings.Controls.OBC.CDL.Interfaces.RealInput | uTSup | Signal for supply air temperature control (T Sup Control Loop Signal in diagram) | |
| Buildings.Controls.OBC.CDL.Interfaces.RealInput | uOutDam_min | Minimum economizer damper position limit as returned by the damper position limits sequence | |
| Buildings.Controls.OBC.CDL.Interfaces.RealInput | uOutDam_max | Maximum economizer damper position limit as returned by the economizer enable-disable sequence. If the economizer is disabled, this value equals uOutDam_min | |
| Buildings.Controls.OBC.CDL.Interfaces.RealInput | uRetDam_min | Minimum return air damper position limit as returned by the economizer enable-disable sequence | |
| Buildings.Controls.OBC.CDL.Interfaces.RealInput | uRetDam_max | Maximum return air damper position limit as returned by the economizer enable-disable sequence | |
| Buildings.Controls.OBC.CDL.Interfaces.RealOutput | yOutDam | Economizer damper commanded position | |
| Buildings.Controls.OBC.CDL.Interfaces.RealOutput | yRetDam | Return air damper commanded position |
Revisions
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August 1, 2020, by Jianjun Hu:
First implementation.