Exhaust Air Transfer Rate (EATR) function controls pressure difference between supply and extract air chambers to minimize adverse air mixing.


Due to the design features (mainly because of heat wheel build) the supply air and the extract air chambers in the AHU are not completely air tight. The dis-balance in the air pressures between these chambers results internal air leakage and might lead to unintentional partial recirculation of the extract air. The EATR control help to avoid this by equalizing pressure between the chambers or creating slight under-pressure in the extract air chamber for intentional leakage of the fresh air.


The pressure in the extract air chamber is adjusted by regulating the air flow with the extract air damper. The damper is partially closed while the extract air fan continues to run to its setpoint. As a result, the chamber gets under-pressurized which prevent leaking of the contaminated extract air.

Start up position

Start up position can be chosen from auto (according to EATR damper settings), settable (from 0 % to maximum damper output limit) or last known position before shutting down (last known position output multiplied by 0,8 to prevent over-pressure alarm loop in worst case scenario). Selected position is fixed during unit start up time + start up delay for EATR. When the unit starts for the first time or there is no data about last known position, EATR damper position is 0 % with “Last known” selection.

Start up delay

Start up delay defines the time when EATR starts regulation. Time is counted from the point when the unit went from starting up to normal speed mode (Low speed mode / High speed mode). This is the time when EATR PID output calculation is released from zero point.

Output limits

Minimum and maximum outputs show closing percentage of the extract damper. Maximum limit is limited not to let damper fully close (Output max limit 100 %) while AHU is running. Default max limit output is 70 %. In case of fire alarm the EATR can be set to 0%, 100% or "Auto" signal output.The EATR control output signal can also be preset to 0..100% while Recirculation mode is active.

Neutral zone EATR

Neutral zone of pressure transmitter indicates value of pressure from setpoint when there is no impact to EATR output and EATR PID output. Set value works in both sides – up and down from the setpoint. Default neutral zone value – 4 Pa ( 2 Pa to the EATR setpoint).



Configuration of the EATR


Variable

Available options & Selection

Note


Activate function

Configuration > Functions > Function activation >


EATR control

| No | Yes |



Configure function

Configuration > Functions > EATR control

EATR control output when

recirculation/support

[0] %


EATR control output min limit

[0] %

Limiting of the EATR output signal (end positions of the EATR control damper)

EATR control output max limit

[70] %

EATR control output when fire mode

| 0% | 100% | Auto |

more about fire mode

Neutral zone of pressure transmitter

[4] Pa


EATR control start up delay

[0] s


EATR control starting point

[0] %


EATR control start up position

| Auto | Max output limit |

| Last known position |



PID Settings

Configuration > PID controllers > EATR control

P-band

[300] Pa


I-time

[100] s


D-time

[0] s



Interface

Configuration > I/O allocation settings >

Analog inputs > Pressure EATR

Any available I/O

Differential pressure transmitter

Analog outputs > EATR Control


Control signal to hardwired actuator.

The AO can stay unconfigured for modbus type actuator.


Configuration of modbus actuator


Operational settings

Data & Settings > Operation overview > EATR control

Pressure EATR

__ Pa

Actual pressure difference

Setpoint EATR

[50.0] Pa

The desired pressure difference between the chambers:


Positive value indicates that pressure in the supply air chamber is higher than in the extract air chamber.

Negative value indicates that pressure in the supply air chamber is lower than in the extract air chamber.

EATR control

__ %


Alarm settings

Configuration > Alarms > Extra functions > 239 High pressure EATR


Action

[ Fast Stop ]


Level

[ Class A ]


Delay

[0] s

Alarm is triggered if EATR pressure is higher than 100 Pa longer than delay time

Limit

[100.0] Pa

Name

[ High pressure EATR ]



Graphical representation

Flowchart > EATR control DPT


Value indicates the difference of air pressure in Supply vs. Extract air chambers:


Positive value indicates that pressure in the supply air chamber is higher than in the extract air chamber.


Negative value indicates that pressure in the supply air chamber is lower than in the extract air chamber.

Flowchart > EATR damper


Indication:


0% - Open

100% - Fully closed


Chapter info                              

Last reviewed: 02/07/2023

Access version: 4.7-1-00 (64)