Main Control & Safety Features; Figure 11: Xcm25D Controller Functionality Overview - Emerson Copeland Eazycool OMTE-90D-TFD Application Manuallines

Condenser fan
control
Monitoring of the discharge
line temperature

Figure 11: XCM25D controller functionality overview

2.8.3 Main control & safety features
Suction pressure control: Each unit is equipped with a suction pressure transmitter. The XCM25D
controls the suction pressure by evaluating the input signal of the pressure transmitter. The suction
pressure regulation for OMTE or OLTE units must be defined by the setpoint (C16) and proportional
band (C17). The signal of the suction pressure transmitter is also used for additional functionalities.
Condensing pressure control: Each unit is equipped with a high-pressure transmitter. The
XCM25D controls the condensing pressure by regulating the fan speed corresponding to the ambient
temperature. The unit controller regulates the condensing pressure with a constant temperature
difference to the ambient ("floating HP"; factory setting E66 = 8K).
Different control options are available. As soon as fan modulation is enabled (E01 = "2-Modulated
fan") parameter E38 allows to choose "floating HP" (factory setting) or control of condensing
temperature inside compressor envelope. In this mode, the compressor can run different minimum
condensing temperatures based on the suction pressure of the compressor. This is the most energy-
efficient way to minimize the condensing temperature as much as possible. But it also means that
the fan is running full speed more often than in floating HP mode.
Automatic liquid injection on OLTE: A mechanical injection valve (LIV) allows liquid refrigerant to
be injected into the scroll set of the compressor to reduce discharge temperatures generated when
the unit operates at increasing compression ratios. There is a bulb on each compressor top cap
connected to the injection valve which allows individual regulation for each compressor. On Digital
models a solenoid valve (normally closed NC) is energized in parallel to the digital modulation
solenoid valve to avoid injection during part-load conditions. The discharge line protection achieved
with discharge line thermostats (B11 & B12; Klixon), installed directly on the discharge pipe.
Compressor phase reversal: Ensures that the compressors keep running in one direction only
(clockwise = right rotation) – necessary for a compliant Scroll compressor to compress and pump
refrigerant. Reset is automatic once the phase rotation is correct for the compressor.
Motor current overload protection: The motor current overload protection is achieved by
adjustable motor circuit breaker Q02 & Q03.
Fixed high-pressure switches: This is a non-adjustable protection device designed to prevent the
compressor from operating outside of its safe high-pressure range. Reset is automatic.
▪
OMTE & OLTE models:
The high-pressure cut-out device is in the same safety chain as the discharge line thermostat. The
alarm provided by the XCM25D does not indicate if it is high pressure or high discharge temperature
alarm.
Adjustable high-pressure limitation: The unit controller provides the possibility to stop the unit at
a critical discharge pressure which is lower than the cut-out value of the fixed high-pressure switch.
High-pressure alarm value can be adjusted by parameter E58.
Discharge temperature protection: Each unit is equipped with a discharge line thermostats (DLT).
The DLT's are in the same safety chain as the high-pressure cut-out switches and a common alarm.
Each compressor has its own safety chain. In addition, there is a discharge line sensor installed on
12
Digital Scroll
control
Electrical
protection
28.8 bar cut-out / 24 bar cut-in.
Liquid injection
Superheat
control
Alarm
management
C6.1.9/0219/E