blockEnable

Sequence for enabling and disabling tower fan
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Information

Block that outputs signal yTowSta for enabling and disabling the cooling tower fan. This is implemented according to ASHRAE Guideline 36-2021, section 5.20.12.2, item a.11-l2.

  1. Disable the tower fans if either:
    • If the plant requires chiller head pressure control (need_heaPreCon) and any enabled chiller’s head pressure control maximum tower fan speed uMaxSpeSet has equaled tower minimum speed fanSpeMin for 5 minutes, or
    • Tower fans uFanSpe have been at minimum speed fanSpeMin for 5 minutes and tower temperature TTow drops below setpoint TTowSet minus 1 °F.
  2. Enable the tower fans if:
    • They have been off (uTow=false) for at least 1 minute, and
    • The tower temperature TTow rises above setpoint TTowSet by 1 °F, and
    • If the plant requires chiller head pressure control (need_heaPreCon) and all enabled chillers’ head pressure control maximum tower fan speed uMaxSpeSet are greater than the tower minimum speed fanSpeMin.
  3. When all condenser water pumps are commanded OFF, disable the PID loop and stop all tower fans.

Note that the tower temperature TTow could be condenser water return temperature or condenser water supply temperature, depending on whether the fan speed control is to maintain return temperature or supply temperature.

Parameters

TypeNameDefaultDescription
Booleanneed_heaPreContrueTrue: the plant requires chiller head pressure being controlled
IntegernChi2Total number of chillers
IntegernTowCel4Total number of cooling tower cells
RealfanSpeChe0.01Lower threshold value to check fan speed
RealfanSpeMin0.1Minimum tower fan speed
Advanced
RealcheMinFanSpe300Threshold time for checking duration when tower fan equals to the minimum tower fan speed
RealcheMaxTowSpe300Threshold time for checking duration when any enabled chiller maximum cooling speed equals to the minimum tower fan speed
RealcheTowOff60Threshold time for checking duration when there is no enabled tower fan

Connectors

TypeNameDefaultDescription
Buildings.Controls.OBC.CDL.Interfaces.RealInput[nChi]uMaxSpeSetMaximum cooling tower speed setpoint from each chiller head pressure control loop
Buildings.Controls.OBC.CDL.Interfaces.RealInputuFanSpeMeasured tower fan speed
Buildings.Controls.OBC.CDL.Interfaces.RealInputTTowSetSetpoint of tower temperature, could be condenser water return or supply temperature
Buildings.Controls.OBC.CDL.Interfaces.RealInputTTowMeasured tower temperature, could be condenser water return or supply temperature
Buildings.Controls.OBC.CDL.Interfaces.BooleanInput[nTowCel]uTowCooling tower operating status: true=running tower cell
Buildings.Controls.OBC.CDL.Interfaces.IntegerInputuConWatPumNumNumber of enabled condenser water pumps
Buildings.Controls.OBC.CDL.Interfaces.BooleanOutputyTowTower fan status: true=enable any number of fans; false=disable all fans

Revisions

  • August 9, 2019, by Jianjun Hu:
    First implementation.