blockSeparateWithDP

Outdoor air and return air damper position limits for units with separated minimum outdoor air damper and differential pressure control

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Information

Block that outputs the position limits of the return and outdoor air damper for units with a separated minimum outdoor air damper and differential pressure control. It is implemented according to Section 5.16.4 of the ASHRAE Guideline 36, May 2020.

Differential pressure setpoint across the minimum outdoor air damper

Per Section 3.2.1, designer should provide the design minimum pressure difference across the minimum outdoor air damper, dpDesMinOutDam. The absolute minimum pressure difference (dpAbsMinOutDam) should also be provided if complying with California Title 24 requirements.
Calculate the outdoor air set point with Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.SetPoints.OutdoorAirFlow.ASHRAE62_1.AHU if complying with ASHRAE 62.1 requirements. Otherwise, see the set points in Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.SetPoints.OutdoorAirFlow.Title24.AHU if complying with Title 24 requirements.
The minimum outdoor air differential pressure set point shall be calculated per Section 5.16.4.1 (if complying with ASHRAE 62.1 requirements) or Section 5.16.4.2 (if complying with Title 24 requirements).

Open minimum outdoor air damper

Open minimum outdoor air damper when the supply air fan is proven ON and the system is in occupied mode and the minimum differential pressure set point is greater than zero. Damper shall be closed otherwise.

Return air damper

Return air damper minimum outdoor air control is enabled when the minimum outdoor air damper is open and the economizer outdoor air damper is less than a projected position limit, which is 5% when supply fan speed is at 100% design speed proportionally up to 80% when the fan is at minimum speed.
Return air damper minimum outdoor air control is disabled when the minimum outdoor air damper is closed or the economizer outdoor air damper is 10% above the projected position limit as determined above.
When enabled, the maximum return air damper set point is modulated from 100% to 0% to maintain the differential pressure across the minimum outdoor air damper at set point.

Parameters

Type	Name	Default	Description
Buildings.Controls.OBC.ASHRAE.G36.Types.VentilationStandard	venStd		Ventilation standard, ASHRAE 62.1 or Title 24
Boolean	have_CO2Sen	false	True: some zones have CO2 sensor
Real	dpAbsMinOutDam	5	Absolute minimum pressure difference across the minimum outdoor air damper. It provides the absolute minimum outdoor airflow
Real	dpDesMinOutDam	20	Design minimum pressure difference across the minimum outdoor air damper. It provides the design minimum outdoor airflow
Real	minSpe		Minimum supply fan speed
DP control
Buildings.Controls.OBC.CDL.Types.SimpleController	dpCon	Buildings.Controls.OBC.CDL.Types.SimpleController.PI	Type of differential pressure setpoint controller
Real	kDp	1	Gain of controller
Real	TiDp	0.5	Time constant of integrator block
Real	TdDp	0.1	Time constant of derivative block
Commissioning › Physical damper position limits
Real	retDamPhy_max	1	Physically fixed maximum position of the return air damper
Real	retDamPhy_min	0	Physically fixed minimum position of the return air damper
Real	outDamPhy_max	1	Physically fixed maximum position of the outdoor air damper
Real	outDamPhy_min	0	Physically fixed minimum position of the outdoor air damper

Connectors

Type	Name	Description
Buildings.Controls.OBC.CDL.Interfaces.RealInput	effAbsOutAir_normalized	Effective minimum outdoor airflow setpoint, normalized by the absolute outdoor airflow rate
Buildings.Controls.OBC.CDL.Interfaces.RealInput	uCO2Loo_max	Maximum zone CO2 control loop
Buildings.Controls.OBC.CDL.Interfaces.RealInput	effDesOutAir_normalized	Effective minimum outdoor airflow setpoint, normalized by the design outdoor airflow rate
Buildings.Controls.OBC.CDL.Interfaces.RealInput	dpMinOutDam	Measured pressure difference across the minimum outdoor air damper
Buildings.Controls.OBC.CDL.Interfaces.RealInput	VOutMinSet_flow_normalized	Effective minimum outdoor airflow setpoint, normalized by design minimum outdoor airflow rate
Buildings.Controls.OBC.CDL.Interfaces.BooleanInput	u1SupFan	Supply fan proven on
Buildings.Controls.OBC.CDL.Interfaces.IntegerInput	uOpeMod	AHU operation mode status signal
Buildings.Controls.OBC.CDL.Interfaces.RealInput	uOutDam	Economizer outdoor air damper commanded position
Buildings.Controls.OBC.CDL.Interfaces.RealInput	uSupFan	Commanded supply fan speed
Buildings.Controls.OBC.CDL.Interfaces.BooleanOutput	y1MinOutDam	Status of minimum outdoor air damper position, true means it's open
Buildings.Controls.OBC.CDL.Interfaces.RealOutput	yOutDam_min	Physically minimum outdoor air damper position limit
Buildings.Controls.OBC.CDL.Interfaces.RealOutput	yOutDam_max	Physically maximum outdoor air damper position limit
Buildings.Controls.OBC.CDL.Interfaces.RealOutput	yRetDam_min	Minimum return air damper position limit
Buildings.Controls.OBC.CDL.Interfaces.RealOutput	yRetDam_max	Maximum return air damper position limit
Buildings.Controls.OBC.CDL.Interfaces.RealOutput	yRetDamPhy_max	Physical maximum return air damper position limit. Required as an input for the economizer enable disable sequence

Components

Type	Name	Default	Description
Buildings.Controls.OBC.CDL.Reals.Multiply	minDp		Minimum pressure difference setpoint when complying with ASHRAE 62.1
Buildings.Controls.OBC.CDL.Reals.PIDWithReset	maxRetDam		Maximum return air damper position

Revisions

August 29, 2023, by Hongxiang Fu:
Because of the removal of Logical.And3 based on ASHRAE 231P, replaced it with a stack of two Logical.And blocks. This is for #2465.
August 1, 2020, by Jianjun Hu:
First implementation.