Emerson E2 Manuel D’Utilisation

The E2 BX can control three different types of AHU 

fans. However, only one fan can be controlled per AHU. 
The fan types include: single-speed, two-speed, and vari-
able-speed. Controls for all fans are similar in that they 
operate in either of three modes:

• Continuous - The fan is always on, even 

when the AHU is not in heating, cooling, or 
dehumidification mode.

• Auto - The fan is only on when the AHU is 

in heating, cooling, or dehumidification 
mode.

• Summer ON, Winter Auto - This mode 

allows the AHU fan to operate in Continuous 
mode during the summer months and in 
Auto mode during the winter months.

The operation of the fans during Continuous and Auto 

modes is largely dependent on the fan type. 

Single-speed fans require no advanced control parame-

ters. Whether in Continuous or Auto mode, the fan will 
be ON when Fan Control calls for it to be ON, and OFF 
when it calls for it to be OFF.

Two-speed fans have a LOW and a HIGH speed set-

ting. You must specify the number of the stage that, when 
activated, will switch the fan from LOW to HIGH.

For example, if there are four cooling stages and you 

wish to have the fan switch from LOW to HIGH when 
stage 3 becomes active, enter a “3” as the switch-over set-
point. This will cause the fan to switch to HIGH speed 
when stage 3 is activated. Likewise, when stage 3 is deac-
tivated, the fan speed will switch from HIGH to LOW.

You may choose a different switch-over setpoint for 

occupied heating, occupied cooling, unoccupied heating, 
and unoccupied cooling modes.

When the AHU is in dehumidification mode, the AHU 

Control application will ignore the fan speed settings of 
the active stages and switch to a user-specified dehumidi-
fication speed (usually LOW). 
Continuous Two-Speed Fan Operation When All 
Stages Are OFF

When the fan is operating in Continuous mode and all 

heating and cooling stages are OFF, the fan speed will 
default to a user-specified speed. You may choose a differ-
ent default speed for both occupied and unoccupied opera-
tion.

Variable-speed fans may operate at any percentage of 

its maximum speed. The method AHU Control uses to 
determine the speed percentage is dependent on whether 
the heat and cool outputs are staged or modulating.
Variable-Speed Fan Operation

For staged AHU outputs, each stage must be pro-

grammed with its own speed percentage setpoint. The 
AHU Control application looks at all of the active stages, 
takes the highest speed percentage setpoint, and operates 
the fan at this speed. 

For example, if cool stage 1 is active with a 30% speed 

percentage setpoint, the fan will likewise operate at 30% 
speed. If a second stage with a setpoint of 50% were to 
become active, the fan speed would increase to 50%.

For each heating and cooling stage, you may specify 

both occupied and unoccupied speed percentage setpoints.
Dehumidification with VS Fans

When in dehumidification mode, a user-defined slow-

down percentage is subtracted from the variable-speed fan 
percentage. This percentage will continue to be subtracted 
until the AHU exits dehumidification mode.