Figure 7: Xcm25D Controller Functionality Overview - Emerson Copeland EazyCool ZXME020E Application Manuallines

Condenser fan
control
Monitoring of the discharge
line temperature

Figure 7: XCM25D controller functionality overview

2.9.3 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. When using
a digital unit (ZXDE), the setpoint (C16) and proportional band (C17) need to be adjusted. The suction
pressure regulation for ZXME or ZXLE units has to be defined by compressor cut-in (C01) and cut-
out (C02) values. The signal of the suction pressure transmitter is also used for additional
functionalities, pump-down and keeping the compressor running within the approved envelopes.
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 high-
pressure transmitter signal. The unit controller can regulate the condensing pressure in two ways.
The first approach is to keep a constant condensing temperature. This mode is utilized by the factory
settings. The pre-adjusted setpoint is 27°C as a universal setting. If lower condensing pressure is
required set up the condenser setpoint (E39) to a lower value. The second control way is fan
modulation based on compressor envelope. This mode of setpoint control is only available if a suction
pressure input is not used. The parameter (E38) enables/disables the mode as needed. If this
function is unused, the condensing temperature setpoint will be set as a parameter (E39) value. The
compressor is allowed to 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.
Automatic liquid injection on ZXME: The electronic controller automatically instructs liquid
refrigerant to be injected into the suction line of the Scroll compressor to reduce discharge
temperatures generated when the unit operates at increasing compression ratios. The electronic
controller reacts automatically to a thermistor which is attached to the discharge line on all ZXME
units. The controller converts this signal for the linear stepper motor driving the liquid injection valve
to a position that enables the compressor to continue operating within its safe envelope.
Automatic enhanced vapour injection (EVI) on ZXLE: Control of an electronic expansion device
based on the superheat in the additional heat exchanger for the EVI Scroll compressor to create
subcooling in liquid refrigerant coming from the receiver. In case of excessive discharge line
temperatures (DLT) the superheat control is ignored and the controller will work in liquid injection
mode in order to reduce the discharge gas temperature.
NOTE: The ZXLE units have an additional subcooling of about 30K. This must be considered
when selecting the expansion device.
Compressor phase reversal: Ensures that the compressor keeps 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: This feature eliminates the need for external current protection
for the compressor motor.
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 for a set
number of trips (7) then the unit will lock out and require manual restart. This feature is important to
prevent the ZX unit from cycling under these controls for a long period of time.
C6.1.6/0117-1017/E
Digital Scroll
control (ZXDE)
Electrical
protection
Liquid injection
(ZXME)
Superheat
control EVI
(ZXLE)
Alarm
management
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