blockExhaustDamper

Control of actuated exhaust dampers without fans

Information

Control sequence for exhaust dampers without fans. It is implemented according to ASHRAE Guidline 35 (G36), PART 5.N.8.(for multi zone VAV AHU), PART 5.P.6 and PART3.2B.3 (for single zone VAV AHU).

Single zone VAV AHU: Control of actuated exhaust dampers without fans (PART 5.P.6)

Exhaust damper position setpoints (PART3.2B.3)
- minExhDamPos is the exhaust damper position that maintains a building pressure of 12 Pa (0.05 inchWC) while the system is at minOutPosMin (i.e., the economizer damper is positioned to provide minimum outdoor air while the supply fan is at minimum speed).
- maxExhDamPos is the exhaust damper position that maintains a building pressure of 12 Pa (0.05 inchWC) while the economizer damper is fully open and the fan speed is at cooling maximum.
The exhaust damper is enabled when the associated supply fan is proven on and any outdoor air damper is open uOutDamPos > 0 and disabled and closed otherwise.
The exhaust damper position is reset linearly from minExhDamPos to maxExhDamPos as the commanded economizer damper position goes from minOutPosMin to outDamPhyPosMax.

The control sequence is as follows:

Image of the exhaust damper control chart for single zone AHU

Parameters

Type	Name	Default	Description
Nominal parameters
Real	minExhDamPos	0.2	Exhaust damper position maintaining building static pressure at setpoint when the system is at minPosMin
Real	maxExhDamPos	0.9	Exhaust damper position maintaining building static pressure at setpoint when outdoor air damper is fully open and fan speed is at cooling maximum
Real	minOutPosMin	0.4	Outdoor air damper position when fan operating at minimum speed to supply minimum outdoor air flow
Real	outDamPhyPosMax	1	Physical or at the comissioning fixed maximum position of the outdoor air damper

Connectors

Type	Name	Description
Buildings.Controls.OBC.CDL.Interfaces.BooleanInput	uSupFan	Supply fan status
Buildings.Controls.OBC.CDL.Interfaces.RealInput	uOutDamPos	Outdoor air damper position
Buildings.Controls.OBC.CDL.Interfaces.RealOutput	yExhDamPos	Exhaust damper position

Components

Type	Name	Description
Buildings.Controls.OBC.CDL.Reals.Line	exhDamPos	Linearly map exhaust damper position to the outdoor air damper position
Buildings.Controls.OBC.CDL.Reals.Switch	swi1	Check if exhaust damper should be open
Buildings.Controls.OBC.CDL.Reals.Hysteresis	greThr	Check if outdoor air damper is open
Buildings.Controls.OBC.CDL.Logical.And	and2	Check if exhaust damper should be activated

Revisions

October 18, 2017, by Michael Wetter:
Revised documentation.
May 12, 2017, by Jianjun Hu:
First implementation.