Access Configuration Manual

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).