modelCoolingTowersWithBypass

Cooling tower system with bypass valve

Extends from Buildings.Fluid.Interfaces.PartialTwoPortInterface.

Information

This model simulates parallel connected cooling tower subsystem with a bypass valve.

The bypass valve is controlled to enforce that the leaving condenser water temperature does not drop below the minimum temperature TMin.

By default, the condenser water setpoint is the ambient wet bulb temperature TWetBul plus the approach temperature dTApp.

Inside the model, a cooling tower fan speed controller is also implemented to maintain the condenser water at its setpoint.

Parameters

Type	Name	Default	Description
Integer	num	2	Number of cooling towers
Modelica.Units.SI.PressureDifference	dpValve_nominal		Nominal pressure difference of the valve
Dynamics › Conservation equations
Modelica.Fluid.Types.Dynamics	energyDynamics	Modelica.Fluid.Types.Dynamics.FixedInitial	Type of energy balance: dynamic (3 initialization options) or steady state
Dynamics › Time needed to open or close valve
Boolean	use_strokeTime	true	Set to true to continuously open and close valve
Dynamics
Modelica.Units.SI.Time	strokeTime	30	Time needed to change valve position from 0 to 1
Nominal condition
Modelica.Units.SI.Pressure	dp_nominal		Nominal pressure difference of the tower
Real	ratWatAir_nominal	0.625	Design water-to-air ratio
Heat transfer
Modelica.Units.SI.Temperature	TAirInWB_nominal		Nominal outdoor (air inlet) wetbulb temperature
Modelica.Units.SI.Temperature	TWatIn_nominal		Nominal water inlet temperature
Modelica.Units.SI.TemperatureDifference	dT_nominal		Temperature difference between inlet and outlet of the tower
Fan
Modelica.Units.SI.Power	PFan_nominal		Fan power
Control Settings
Modelica.Units.SI.TemperatureDifference	dTApp	3	Approach temperature
Modelica.Units.SI.Temperature	TMin		Minimum allowed water temperature entering chiller
Modelica.Blocks.Types.SimpleController	controllerType	Modelica.Blocks.Types.SimpleController.PI	Type of fan speed controller
Real	k	1	Gain of the tower PID controller
Modelica.Units.SI.Time	Ti	60	Integrator time constant of the tower PID controller
Modelica.Units.SI.Time	Td	0.1	Derivative time constant of the tower PID controller

Components

Type	Name	Description
Modelica.Blocks.Interfaces.BooleanInput[num]	on	On signal for cooling towers
Modelica.Blocks.Interfaces.RealInput	TWetBul	Entering air wetbulb temperature
Modelica.Blocks.Interfaces.RealOutput[num]	PFan	Electric power consumed by fan
Modelica.Blocks.Interfaces.RealOutput	TLvg	Leaving water temperature
Buildings.DHC.Plants.Cooling.Subsystems.CoolingTowersParallel	cooTowSys	Cooling tower system
Buildings.Fluid.Actuators.Valves.TwoWayEqualPercentage	valByp	Condenser water bypass valve
Buildings.Fluid.Sensors.TemperatureTwoPort	senTCWSup	Temperature sensor
Buildings.Controls.OBC.CDL.Reals.Sources.Constant	TSetByp	Bypass loop temperature setpoint
Buildings.Controls.OBC.CDL.Reals.PIDWithReset	bypValCon	Bypass valve controller
Buildings.Controls.OBC.CDL.Reals.PID	cooTowSpeCon	Cooling tower fan speed controller
Buildings.Controls.OBC.CDL.Reals.Switch	swi	Output the input of higher value
Buildings.Controls.OBC.CDL.Reals.Hysteresis	hys	Compare if (TWetBul+dTApp) is greater than TMin
Buildings.Controls.OBC.CDL.Reals.AddParameter	addPar	Add approach temperature on top of wetbulb temperature
Buildings.Fluid.FixedResistances.Junction	jun	Upstream mixing point of cooTowSys and valByp

Revisions

January 2, 2023, by Kathryn Hinkelman:
Set dp_fixed = 0 for the bypass valve because the pressure drop in this leg will be significantly less than the cooling towers.
Propagated riseTime for the valve signal filters.
November 16, 2022, by Michael Wetter:
Changed rise time of valve to 30 seconds so that it is the same as the one for the pumps, and set use_inputFilter = false for shut-off valve in cooling tower. This avoids a sharp rise in pressure near t=35 seconds.
May 19, 2020 by Jing Wang:
First implementation.