blockReduceDemand
Sequence for reducing operating chiller demand
Information
Block that reduces demand of current operating chillers when there is a stage-up command, according to ASHRAE Guideline 36-2021, section 5.20.4.16, item a which specifies how to start the stage-up process of the current operating chillers; and section 5.20.4.17, item a.1 which specifies how to start the stage-down process of the current operating chiller when the stage-down process requires one chiller off and another chiller on.
When there is a stage-up command,
-
Command operating chillers to reduce demand to
chiDemRedFacof their current load, e.g., 75%. -
Wait until actual demand < 80% of current load up to a maximum of
holChiDemTim(e.g., 5 minutes) before proceeding.
When there is a stage-down command (uStaDow=true) and the process
requires a smaller chiller to be enabled and a larger chiller to be disabled
(uOnOff=true),
-
Command operating chillers to reduce demand to
chiDemRedFacof their current load, e.g., 75% or a percentage equal to current stage minimum cycling operative partial load ratioyOpeParLoaRatMin, whichever is greater. -
Wait until actual demand < 80% of current load up to a maximum of
holChiDemTim(e.g., 5 minutes) before proceeding.
Parameters
| Type | Name | Default | Description |
|---|---|---|---|
| Integer | nChi | 2 | Total number of chillers in the plant |
| Real | chiDemRedFac | 0.75 | Demand reducing factor of current operating chillers |
| Real | holChiDemTim | 300 | Maximum time to wait for the actual demand less than percentage of current load |
Connectors
| Type | Name | Default | Description |
|---|---|---|---|
| Buildings.Controls.OBC.CDL.Interfaces.BooleanInput | uDemLim | Demand limit: true=limit chiller demand | |
| Buildings.Controls.OBC.CDL.Interfaces.RealInput | uChiLoa | Current chiller load | |
| Buildings.Controls.OBC.CDL.Interfaces.RealInput | yOpeParLoaRatMin | Current stage minimum cycling operative partial load ratio | |
| Buildings.Controls.OBC.CDL.Interfaces.BooleanInput | uStaDow | Stage down status: true=stage-down | |
| Buildings.Controls.OBC.CDL.Interfaces.BooleanInput | uOnOff | True: if the stage change require one chiller to be enabled while another is disabled | |
| Buildings.Controls.OBC.CDL.Interfaces.BooleanInput[nChi] | uChi | Chiller status: true=ON | |
| Buildings.Controls.OBC.CDL.Interfaces.RealOutput | yChiDem | Chiller demand setpoint | |
| Buildings.Controls.OBC.CDL.Interfaces.BooleanOutput | yChiDemRed | Flag: true if it is not requiring reducing demand or the chiller demand reduction process has finished |
Revisions
-
September 17, 2019, by Jianjun Hu:
First implementation.