blockEconomizer

Controller for economizer

Information

This is a controller for an economizer, that adjusts the mixed air dampers to fulfill three control functions.

Freeze protection, based on the mixed air temperature measurement
Minimum outside air requirement, based on the outdoor air flow rate measurement
Supply air cooling, based on the logic implemented in Buildings.Examples.VAVReheat.BaseClasses.Controls.SupplyAirTemperature, with the additional condition that when the outside air dry bulb is greater than the return air dry bulb, economizer cooling is disabled.

Type	Name	Default	Description
Boolean	have_reset	false	Set to true to reset the outdoor air damper controllers with the enable signal
Boolean	have_frePro	false	Set to true to enable freeze protection (mixed air low temperature control)
Modelica.Units.SI.Temperature	TFreSet	277.15	Lower limit of mixed air temperature for freeze protection
Modelica.Units.SI.TemperatureDifference	dTLock	1	Temperature difference between return and outdoor air for economizer lockout
Modelica.Units.SI.VolumeFlowRate	VOut_flow_min		Minimum outside air volume flow rate
Modelica.Blocks.Types.SimpleController	controllerType	Modelica.Blocks.Types.SimpleController.PI	Type of controller
Real	k	0.05	Gain of controller
Modelica.Units.SI.Time	Ti	120	Time constant of integrator block

Type	Name	Description
Buildings.Controls.OBC.CDL.Interfaces.BooleanInput	uEna	Enable signal for economizer
ControlBus	controlBus	Control bus
Modelica.Blocks.Interfaces.RealInput	uOATSup	Control signal for outdoor air damper from supply temperature controller
Modelica.Blocks.Interfaces.RealInput	TMix	Measured mixed air temperature
Modelica.Blocks.Interfaces.RealInput	VOut_flow	Measured outside air flow rate
Modelica.Blocks.Interfaces.RealInput	TRet	Return air temperature
Modelica.Blocks.Interfaces.RealOutput	yRet	Control signal for return air damper
Modelica.Blocks.Interfaces.RealOutput	yOA	Control signal for outside air damper

Type	Name	Description
Modelica.Blocks.Math.Gain	gain	Normalize mass flow rate
Buildings.Controls.OBC.CDL.Reals.PID	conV_flow	Controller for outside air flow rate
Modelica.Blocks.Sources.Constant	uni	Unity signal
Modelica.Blocks.Sources.Constant	closed	Signal to close OA damper
Buildings.Controls.OBC.CDL.Reals.PID	yOATFre	Controller of outdoor damper to track freeze temperature setpoint
Buildings.Controls.OBC.CDL.Reals.Min	minFrePro	Takes lower signal (limits damper opening for freeze protection)
Modelica.Blocks.Sources.Constant	TFre	Setpoint for freeze protection
Buildings.Controls.OBC.CDL.Reals.Subtract	invSig	Invert control signal for interlocked damper
Modelica.Blocks.Logical.Hysteresis	hysLoc	Hysteresis for economizer lockout
Modelica.Blocks.Math.Feedback	feedback
Buildings.Controls.OBC.CDL.Reals.Switch	swiOA	Switch to close outdoor air damper
Modelica.Blocks.Sources.Constant	one	Fill value in case freeze protection is disabled
Buildings.Controls.OBC.CDL.Reals.Switch	swiModClo	Switch between modulating or closing outdoor air damper
Buildings.Controls.OBC.CDL.Reals.Max	maxOutDam	Select larger of the outdoor damper signals
Buildings.Controls.OBC.CDL.Reals.Sources.Constant	conOne	Constant 1

August 31, 2021, by Michael Wetter:
Corrected selection of control signal during freeze protection.
October 27, 2020, by Antoine Gautier:
Refactored for compatibility with new supply air temperature control.
This is for #2024.
July 10, 2020, by Antoine Gautier:
Added optional reset signal. Corrected connections to yOATFre.
This is for #2019 and #1995.
December 20, 2016, by Michael Wetter:
Added type conversion for enumeration when used as an array index.
This is for #602.
April 26, 2016, by Michael Wetter:
Changed controller for freeze protection as the old implementation closed the outdoor air damper during summer. This is for #511.