Specifications

ECONOMIZER OPERATION — Economizers are factory
installed on 30GX105-265 units and 30HXA,C161-271 units.
All other sizes use standard EXVs. The economizer im-
proves both the chiller capacity and efficiency as well as pro-
viding compressor motor cooling. Inside the economizer are
both a linear stepper motor (same as standard EXV motor)
and a float valve. The stepper motor is controlled by the pro-
cessor to maintain the desired liquid level in the cooler (as
is done for chillers without economizers). The float valve
maintains a liquid level in the bottom of the economizer.
Liquid refrigerant is supplied from the condenser through
the end to the bottom of the economizer. A bubbler tube sup-
plies a small amount of discharge gas to ensure that the float
will be able to work properly.As the refrigerant passes through
the EXD, its pressure is reduced to an intermediate level of
about 75 psig (517 kPag). This pressure is maintained inside
the economizer shell. Next, the refrigerant flows through the
float valve where its pressure is further reduced to slightly
above the pressure in the cooler.
The increase in performance is achieved when some of
the refrigerant passing through the EXD flashes to vapor,
further subcooling the liquid that is maintained at the bottom
of the economizer. This increase in subcooling provides ad-
ditional capacity. Also, since the additional power required
to accomplish this is minimal, the efficiency of the machine
improves. The vapor that flashes rises to the top of the econo-
mizer where it passes to the compressor and is used to pro-
vide motor cooling. After passing over the motor windings,
the refrigerant reenters the cycle at an intermediate port in
the compression cycle.
Oil Pumps — The 30GX/HX screw chillers use one ex-
ternally mounted prelubricating oil pump per circuit. This
pump is operated as part of the start-up sequence. On 30GX
units, the pumps are mounted to the base rails on the oil sepa-
rator side of the unit. The pumps are mounted to a bracket
on the condensers of 30HXC units and to the oil separator
on 30HXA units.
When a circuit is required to start, the controls energize
the oil pump first and read the oil pressure transducer read-
ing. The pump is operated for a period of 20 seconds, after
which the oil solenoid is energized to open the oil inlet valve
at the compressor. The control again reads the pressure from
the oil pressure transducer. If the pump has built up suffi-
cient oil pressure, the compressor is allowed to start.
Once the compressor has started, the oil pump is turned
off within 10 seconds and is not used again until the next
start-up. If the pump is not able to build up enough oil pres-
sure, the pump is turned off. Within 3 seconds, the pump is
re-energized and makes one additional attempt to build oil
pressure. The control generates an alarm if the second at-
tempt fails.
Motor Cooling — Compressor motor winding tempera-
tures are controlled to a set point of 200 F (93.3 C).
The control accomplishes this by cycling the motor cooling
olenoid valve to allow liquid refrigerant to flow across the
motor windings as needed. On units equipped with econo-
mizers, flash gas leaves the top of the economizer and con-
tinually flows to the motor windings. All refrigerant used for
motor cooling re-enters the rotors through a port located mid-
way along the compression cycle and is compressed to dis-
charge pressure.
Back Pressure Valve (30GX and 30HXA only)
—
This valve is located on the oil separator outlet on 30GX
units and mounted on the oil separator shell of 30HXA units.
The valve’s function is to ensure that there is sufficient sys-
tem differential pressure to allow for oil to be driven back to
the compressor. A small copper line (economizer pressure)
is connected to the top of the valve, which contains an in-
ternal spring that closes a piston if the pressure in the oil
separator is not at least 15 psig greater than the economizer
pressure.
Sensors — The 30GX,HX control system (based on the
Flotronic™ II chiller control system) gathers information from
sensors to control the operation of the chiller. The units use
up to 9 standard pressure transducers, 7 standard thermistors
(including 3 motor temperature thermistors), and 2 liquid level
thermistors to monitor and control system operation. The sen-
sors are listed in Table 2.
Compressor Protection Module (CPM) — Each
compressor has its own CPM. The CPM provides the fol-
lowing functions:
• compressor main contactor control
• Wye-Delta contactor transition
• compressor ground current protection
• motor temperature reading
• high-pressure protection
• reverse rotation protection
• voltage imbalance protection
• current imbalance protection
• compressor oil solenoid control
• motor cooling solenoid control
• sensor bus communications
• starting and running overcurrent protection
The CPM has the following 4 output relays and 4 inputs:
OUTPUTS:
• compressor contactor
• compressor oil solenoid
• compressor motor cooling solenoid
• Wye-Delta transition relay
INPUTS:
• motor temperature
• three-phase voltage
• three-phase current
• high-pressure switch
A diagram of the CPM board is shown in Fig. 1. There are
line voltage inputs at L1, L2, and L3. Below these inputs are
the current toroid inputs at Plug 1. Below Plug 1 are the 3
COMM3 communication terminals. In the lower left corner
of the board are the inputs for motor winding temperature.
The address DIP (dual-in-line package) switch and com-
pressor must-trip amps header are factory set. For compres-
sor A1, switches 2 and 4 should be set. For compressor A2
(30HXA,C206-271 AND 30GX205-265), switches 2, 3, and
4 should be set. For compressor B1, switches 1 and 4 should
be set.
To verify proper must trip amps header configuration, press
and use the up arrow key on the HSIO to locate the
must trip amp values. Press the reset button on the HSIO/
fuse panel to update these values. See Appendix A. If the
values do not match those in Appendix A, verify with Ap-
pendix D that the configuration headers have been properly
punched out.
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