blockLessCoupled
Sequence of defining cooling tower fan speed when the plant is not close coupled
Information
Block that outputs cooling tower fan speed ySpeSet based on the control
of condenser water return temperature for the plant that is not closed coupled.
This is implemented according to ASHRAE Guideline 36-2021, section 5.20.12.2,
item a.8-10.
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When any condenser water pump is proven on (
uConWatPumSpe > 0),
condenser water supply temperature setpoint TConWatSupSet shall be
set equal to the condenser water return temperature setpoint TConWatRetSet
minus a temperature difference. The temperature difference is the 5-minutes rolling
average of common condenser water return temperature TConWatRet less
condenser water supply temperature TConWatSup, sampled at the minimum once
every 30 seconds. When the plant is first enabled, the temperature difference shall
be fixed equal to 50% of the difference between the design condenser water supply
(TConWatSup_nominal) and return (TConWatRet_nominal) temperature
of the enabled chiller for 5 minutes (iniPlaTim).
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When any condenser water pump is proven on (
uConWatPumSpe > 0),
condenser water supply temperature TConWatSup shall be maintained at
setpoint by a direct acting PID loop. The loop output shall be mapped to the
variable tower speed. Reset the tower speed from the minimum tower speed fanSpeMin
at 0% loop output to 100% speed at 100% loop output.
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Tower speed
ySpeSet shall be the lowest value of tower speed
from loop mapping, maximum cooling tower speed setpoint from each chiller head
pressure control loop uMaxSpeSet (if the plant requires the chiller
head pressure being controlled), and tower maximum speed that resets
based on plant partial load ratio plrTowMaxSpe. All operating fans shall
receive the same speed signal.
Parameters
| Type | Name | Default | Description |
|---|
| Boolean | need_heaPreCon | true | True: the plant requires chiller head pressure being controlled |
| Integer | nChi | 2 | Total number of chillers |
| Integer | nConWatPum | 2 | Total number of condenser water pumps |
| Real | fanSpeMin | 0.1 | Minimum cooling tower fan speed |
| Return water temperature controller |
| Real | samplePeriod | 30 | Period of sampling condenser water supply and return temperature difference |
| Real | iniPlaTim | 300 | Threshold time to hold the initial temperature difference at the plant initial stage |
| Real[nChi] | TConWatSup_nominal | {293.15, 293.15} | Design condenser water supply temperature (condenser entering) of each chiller |
| Real[nChi] | TConWatRet_nominal | {303.15, 303.15} | Design condenser water return temperature (condenser leaving) of each chiller |
| Supply water temperature controller |
| Buildings.Controls.OBC.CDL.Types.SimpleController | supWatCon | Buildings.Controls.OBC.CDL.Types.SimpleController.PI | Supply water temperature controller |
| Real | kSupCon | 1 | Gain of controller |
| Real | TiSupCon | 0.5 | Time constant of integrator block |
| Real | TdSupCon | 0.1 | Time constant of derivative block |
| Real | ySupConMax | 1 | Upper limit of output |
| Real | ySupConMin | 0 | Lower limit of output |
Revisions
-
August 9, 2019, by Jianjun Hu:
First implementation.
