VAV ventilation control (VavVntCtl11)

Overview

The application function "VAV ventilation control 11" (VavVntCtl11) collaborates with VAV supply air terminal boxes for ventilation and/or room air quality control.

Function

Different modes are available for ventilation control; the behavior is selectable by parameter.

Ventilation mode
The ventilation mode can be set per room operating mode to:

Off
Minimum (Constant air flow)
Dcv (Demand controlled ventilation) ¹⁾
Dcv & Min (Demand controlled ventilation with a minimum air flow limit) ¹⁾

¹⁾ Air quality sensor required in the room.

The table shows factory default settings for min vent and air quality parameters:

Plant mode	Ventilation mode	Sp air quality [ppm]	AirFlMin [m3/h]
1 Off	Off
2 Protection*	Off	1500	50
3 Economy*	Off	1500	50
4 Pre-Comfort*	Dcv	1100	50
5 Comfort*	Min & Dcv	900	50
6 Warm-up	Off
7 Cool down	Off
8 Room low temperature protection	Off
9 <not used>
10 Free cooling	Depends on ROpMod	Depends on ROpMod	Depends on ROpMod
11 Night cooling	Off
12 Rapid ventilation	s/a Comfort	s/a Comfort	s/a Comfort
13 <not used>
14 Emergency off	Off
15 Max.supply air vol.flow only (positive pressure)	Off
16 Max.extract air vol.flow only (negative pressure)	Off
17 Purge Max.supply and extract air vol. flow	Off

*For these modes the parameters can be individually adjusted.

NOTICE

Minimum ventilation air flow settings in VavVntCtl11

VAV PID controller is not enabled unless ventilation flow setpoint is above 7% of max air flow setting (hardcoded).

If minimum ventilation is required, set minimum ventilation air flow setting(s) >7% of the largest maximum air flow setpoint.

Minimum ventilation setup

Minimum ventilation air flow settings should be >7% of the largest maximum air flow setpoint value (typically cooling flow maximum, VavSuAirFlMaxC located in the segment AF VavSu.xx). The nominal air volume flow parameter (AirFlNom, also located in the segment AF VavSu.xx) should be set equal to this largest maximum air flow setpoint value.

In the following examples, cooling flow maximum (VavSuAirFlMaxC) is assumed to be the largest maximum air flow setpoint.

Example 1
In this example, assume AirFlNom and VavSuAirFlMaxC have both been set to 1000 m3/h, and the minimum ventilation setpoint object (VavSuAflMinVnt, located in the segment AF VavSu.xx) has been set tozero. Setting VavSuAflMinVnt in the segment AF to zero allows the min vent parameter settings in this AF (VAV ventilation control, VavVntCtl11) to vary per the room operating mode (Comfort, Pre-Comfort, Economy, Protection). See table.

Room mode ventilation flow value	Ventilation mode setting	Result
AirFlMinRCmf = 100 m3/h	CmfCnf = Min vent & DCV	In Comfort, ventilation flow will have a low limit of 100 m3/h and may rise with air quality demand (DCV).
AirFlMinRPcf = 80 m3/h	PcfCnf = Min vent	In Pre-Comfort, ventilation flow = 80 m3/h.
AirFlMinREco = 60 m3/h	EcoCnf = Min vent	In Economy, ventilation flow will be zero, because AirFlMinREco was incorrectly set to 60 m3/h which is less than 7% of AirFlNom (AirFlNom was set to 1000 m3/h).
AirFlMinRPrt = 80 m3/h	PrtCnf = Off	In Protection, the mode setting (PrtCnf) has been set to Off. When a ventilation mode setting = Off, ventilation flow for that room mode will be zero regardless of the parameter flow value (in this case, AirFlMinRPrt) or the value of VavSuAflMinVnt.

Example 2
In this example, assume AirFlNom and VavSuAirFlMaxC have both been set to 1000 m3/h, and the minimum ventilation setpoint object (VavSuAflMinVnt) located in the segment AF VavSu.xx has been set to 100 m3/h.

Room mode ventilation flow setting	Ventilation mode setting	Result
AirFlMinRCmf = 125 m3/h	CmfCnf = Min vent	In Comfort, ventilation flow will be 125 m3/h.
AirFlMinRPcf = 90 m3/h	PcfCnf = Min vent	In Pre-Comfort, ventilation flow = 100 m3/h (not 90) because VavSuAflMinVnt was set to 100, which is larger than 90; (90 and 100 are each >7% AirFlNom, so they are both valid (usable) values; when valid settings conflict, the larger value wins).
AirFlMinREco = 50 m3/h	EcoCnf = Min vent	In Economy, ventilation flow will = 100 m3/h because VavSuAflMinVnt was set to 100. Note: it is important to understand that if VavSuAflMinVnt were set to zero as in example 1 above, the minimum ventilation flow for Economy would not = 50 m3/h, even though AirFlMinREco has been set to 50. This is because 50 is not >7% of the maximum flow setpoint (AirFlNom was set to 1000 m3/h). In this case min vent would be zero.
AirFlMinRPrt = 50 m3/h	PrtCnf = Off	In Protection, the mode setting (PrtCnf) has been set to Off. When a ventilation mode setting = Off, ventilation flow for that room mode will be zero regardless of the parameter flow value (in this case, AirFlMinRPrt) or the value of VavSuAflMinVnt.

Demand Controlled Ventilation with Proportional Control - Configuration

Typical DCV (Demand control ventilation) uses only the "P" of the PID control loop. (PID: Proportional gain; Integral; Derivative).

DCV also uses outside air to maintain a ppm differential between good/bad indoor air quality.

When indoor air quality is at or above the hi limit ppm setpoint, PID loop output should be 100%. This control behavior can be configured by adjusting properties of the Ventilation controller object (VntCtr, Ventilation controller).

Set VntCtr properties as follows:

Integral:0
Derivative:0
Controller Output for Offset:100

The Controller Output for Offset parameter determines PID output when the measured value is at setpoint. Reference the specifications document and set accordingly.

Examples of Minimum VS Maximum Ventilation at Setpoint
The left graph shows an example of the behavior of the controller at default settings. The graph on the right shows an example the behavior of the controller after the VntCtr properties have been configured using the settings listed previously in the DCV with Proportional Control section.
Minimum Ventilation at Setpoint (default)	Maximum Ventilation at Setpoint

Periodic air flush
Parameters are available to configure periodic cycling of ventilation air flow. Ventilation can be enabled for minimum air flow at regular intervals, for the length of time in TiOnDutyCyc. See figure.

The length of the duty cycle off interval can be configured for each operating mode (DutyCycCmf, DutyCycPcf, DutyCycEco, DutyCycPrt). A duty cycle of 0min (default) means the feature is disabled.

Note
If the room temperature is measured with an extract air temperature sensor, air must flow to ensure the effective room temperature is measured correctly. In this case, periodic air flush can be used to provide air flow at regular intervals.

Exception handling
For air quality control, the ventilation mode must be set to Dcv or Min & Dcv, VavSuAvlVnt must be Yes and the air quality sensor must be Valid. If the sensor is failed or absent, then the ventilation mode cannot be Dcv or Min & Dcv; in this case VavSuVntReq is set to Min.

Configuration

Objects

Description	Object	Type	Default value
Setpoint room air quality for comfort	SpAQualRCmf	ACnfVal	900 [ppm]
Setpoint room air quality for pre-comfort	SpAQualRPcf	ACnfVal	1100 [ppm]
Setpoint room air quality for economy	SpAQualREco	ACnfVal	1500 [ppm]
Setpoint room air quality for protection	SpAQualRPrt	ACnfVal	1500 [ppm]

Parameters

Description	Parameter	Default value
Comfort configuration 1:Off 2:Minimum ventilation 3:Demand-controled ventilation 4:Minimum ventilation & Demand-controlled ventilation	CmfCnf	4:Minimum ventilation & Demand-controlled ventilation
Pre-Comfort configuration Enumeration see CmfCnf	PcfCnf	3:Demand-controled ventilation
Economy configuration Enumeration see CmfCnf	EcoCnf	2:Minimum ventilation
Protection configuration Enumeration see CmfCnf	PrtCnf	2:Minimum ventilation
Minimum room air volume flow for comfort ▶ When CmfCnf is set to 4:Minimum ventilation & Demand-controlled ventilation and IAQ sensor configured and Valid, damper during Comfort will equal AirFlMinRCmf or the demand-controlled ventilation position, whichever is larger. ▶ When used, air flow minimum settings should be at least 7% of the largest maximum flow setpoint (for example, cooling flow maximum).	AirFlMinRCmf	50 [m³/h] 29.4 [ft³/min] 13.89 [l/s]
Minimum room air volume flow for pre-comfort ▶ Function see CmfCnf	AirFlMinRPcf	50 [m3/h] 29.4 [ft3/min] 13.89 [l/s]
Minimum room air volume flow for economy ▶ Function see CmfCnf	AirFlMinREco	50 [m3/h] 29.4 [ft3/min] 13.89 [l/s]
Minimum room air volume flow for protection ▶ Function see CmfCnf	AirFlMinRPrt	50 [m3/h] 29.4 [ft3/min] 13.89 [l/s]
Air volume flow unit ▶ Defined by selected engineering unit – do not change.	AirFlUnit	[m³/h] [ft³/min] [l/s]
Duty cycling in comfort	DutyCycCmf	0 [min]
Duty cycling in pre-comfort	DutyCycPcf	0 [min]
Duty cycling in economy	DutyCycEco	0 [min]
Duty cycling in protection	DutyCycPrt	0 [min]
Switch-on time duty cycling ▶ If periodic cycling of ventilation air flow is desired, TiOnDutyCyc defines the length of "on" time for the ventilation air flow. Periodic cycling requires duty cycle parameter(s) to be set to non zero value (DutyCycCmf, DutyCycPcf, DutyCycEco, DutyCycPrt).	TiOnDutyCyc	6 [min]

Interface

Interface	Description	Type	Ref.	Owned by
PrSpVnt	Present ventilation setpoint	APrcVal	●	-
VntCtr	Ventilation controller	Controller	●	-
RCtl	Room control	GrpMaster	◉	Room
SpAQualRCmf	Setpoint room air quality for comfort	ACnfVal	●	-
SpAQualRPcf	Setpoint room air quality for pre-comfort	ACnfVal	●	-
SpAQualREco	Setpoint room air quality for economy	ACnfVal	●	-
SpAQualRPrt	Setpoint room air quality for protection	ACnfVal	●	-

Engineering and commissioning

NOTICE

Minimum ventilation air flow settings in VavVntCtl11

VAV PID controller is not enabled unless ventilation flow setpoint is above 7% of max air flow setting (hardcoded).

If minimum ventilation is required, set minimum ventilation air flow setting(s) >7% of the largest maximum air flow setpoint.