Emerson E2 User Manual

The E2 RX refrigeration controller uses suction group 

applications to cycle compressors in an effort to maintain a 
constant suction pressure or temperature in a refrigeration 
system. A suction group may contain up to 16 compressor 
stages (standard, variable-speed, or unloader). 

There are two different types of suction group applica-

tions: 

• Suction Group - The “standard” suction group 

application that has existed since the first version of 
E2 firmware. The Suction Group uses PID Control 
and with proper optimization it can achieve very 
tight suction pressure or temperature control, but 
compressor cycling is not based on load analysis 
and can be inefficient, especially in larger racks. All 
versions of E2 support the standard Suction Group 
application.

• Enhanced Suction Group - Introduced in E2 version 

2.30F01, the Enhanced Suction Group has all of the 
important features of the older Suction Group appli-
cation, but instead of employing user-configured 
PID constants to optimize operation, the Enhanced 
Suction Group determines optimum control by 
“learning” the effect each compressor and circuit 
load has on the suction input. The Enhanced Suc-
tion Group is easier to configure and more conser-
vative with compressor cycling than the standard 
Suction Group. In addition, the Enhanced Suction 
Group also supports use of the Copeland Digital 
Scroll and Copeland Digital Discus compressors.

A Suction Group application looks at suction pressure 

or suction temperature to determine how many compressor 
stages should be ON or OFF. The application compares 
the suction pressure or temperature to its control setpoint 
using PID control. The result of this comparison is a per-
centage from 0% to 100% that corresponds to the total 
capacity of the compressor rack that should be active.

The Suction Group application then takes that percent-

age and determines what combination of compressors 

should be switched ON or OFF to best fulfill the require-
ment. For example, if the application says that 60% of the 
total compressor rack’s power should be active, and the 
rack has compressors totaling 50 HP, then E2 will try to 
switch on compressors totaling 30 HP.

For more information on PID, see Appendix D: PID 

Control.

Suction Group applications are compatible with vari-

able-speed compressors. VS compressors allow Suction 
Group applications to “fine-tune” the amount of total 
active rack horsepower to react to small changes in suction 
pressures or temperatures. As a result, the rack does a bet-
ter job of controlling suction, requiring less compressor 
switches.

When a variable-speed compressor is present, it will 

generally be treated as the primary pressure controlling 
device, and any other standard compressors in the rack are 
secondary devices used only if the VS compressor is 
unable to fully handle the required horsepower. The vari-
able-speed compressor will be the first compressor on and 
the last compressor off.

 The Floating Setpoint strategy within the E2 RX pro-

vides a method for varying the suction setpoint of the 
group based on the temperature within a circuit. When 
Floating Setpoint Control is enabled, the E2 RX monitors 
either a circuit temperature or a case temperature from a 
CC-100 and adjusts the suction setpoint if the temperature 
is too low or too high.

The user establishes a range outside of which the E2 

RX is instructed to make a one PSI adjustment to the suc-
tion pressure setpoint to either reduce or increase the case 
temperature. If the temperature continues to remain out-
side of the range for a user-defined period of time, the E2 
RX continues to make pressure setpoint adjustments until 
the temperature is within the established range.

By varying the suction pressure setpoint to match the 

temperature requirements of the circuit, the E2 RX is able 
to ensure product integrity while achieving maximum rack 
efficiency.

A Suction Group application looks at suction pressure 

or suction temperature and compares it to the suction set-
point to determine whether compressor stages should be