Greenheck MPX (472695) - Manual (Page 21)

Digital Scroll Compressor
If the digital scroll compressor option was selected
for this unit, it is equipped with a Copeland Scroll
Digital™ compressor.
Refrigeration Modulation
Digital scroll compressors modulate the refrigeration
system, producing significant performance benefits.
The compressor output can be modulated from
10% to 100% of capacity by means of “loading” or
“unloading” the refrigerant compression scroll.
A conventional fixed scroll compressor runs at full
load and then shuts down when user set points are
reached. The digital scroll compressor modulates
its cooling capacity by means of cycling through
rapid load/no-load cycles without shutting down
the compressor motor (digital control). Because it
can operate at less than full load, evaporator coil
temperatures are much more constant as hysteresis is
improved and humidity control is enhanced.
Compressor Cycling
The use of a Copeland Scroll Digital™ compressor
in the refrigeration circuit provides energy savings
during normal operation of the unit and also improves
the life expectancy of the system by avoiding on/off
cycling. One of the primary causes of early failure of
a refrigeration system is excessive cycling on and off.
The digital scroll compressor eliminates excessive
cycling by allowing the compressor to continue to
run, but internal compression is eliminated in brief
cycles. Depending on the control signal received from
the digital scroll controller, each 15 second interval is
assigned a varying load/no load run time.
Figure 2
Unloader
Solenoid
Model
Number
Power
Junction Box
Typical Copeland Scroll Digital™ Compressor
with Surface Mounted Unloader Solenoid
Typical Digital Scroll Compressor
with External Unloader Solenoid
Unloader
Solenoid
Refrigerant
Suction Line
Power
Junction
Box
Figure 3
Configuration
In units with more than one compressor, only the lead
compressor will be digital scroll type. Digital scroll
compressors can be identified by the label on the
compressor.
If the third character of the model number is a “D”, the
compressor is digital scroll type. (See Figure 1).
Digital scroll compressors are very similar in
appearance to conventional scroll compressors, but
they will also have an unloader solenoid mounted
either on the side of the compressor (see Figure
2) or on a tube connected to the refrigerant suction
line (see Figure 3). When the unloader solenoid is
energized, the compressor will go into an unloaded
state.
Typical Compressor Label
Figure 1
21 Model MPX Make-Up Air Unit
®