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Section 2 - Product description
An integral liquid cooled, transistorized, PWM, vari-
able speed drive (VSD) is controlled by the chiller
microprocessor control panel to start/stop, select com-
pressors to run, and select compressor speed. Power
Factor is 95% at part or full load.
The chiller microprocessor communicates with the
VSD Logic Board via a 3-wire RS-485 opto coupled
data link. The VSD Logic Board runs the number of
compressors required to meet the load and the com-
pressors to the speed requested by the chiller micro-
processor.
The basic system control architecture is shown in the
diagram below:
CHILLER CONTROL SYSTEM
INPUTS
Pressure Transducers
Temperature Sensors
Level Sensor
Switches
CONTROL
Liquid Flow
High Pressure
PANEL
Start/Stop
(Chiller Control
Board)
Customer Supplied
Contacts
Microprocessor
User Interface
Display
COMMUNICATIONS
Keypad
Building Automation
Printer
Modem
Figure 2 - Chiller control system
The chiller is designed to operate in ambient tempera-
tures of 0°F to 125°F (-18°C to 52°C). Capacity control
is capable of reducing chiller capacity to 10% of full
load without the need for Hot Gas Bypass.
Compressor
The direct drive semi-hermetic rotary twin-screw MTS
compressor is designed for industrial refrigeration ap-
plications and ensures high operational efficiencies
and reliable performance. Capacity control is achieved
by stepless VSD speed changes. No slide valve is re-
quired. Smooth capacity control is achieved between
10% and 100% of chiller capacity in most operating
conditions. The compressor is a positive displacement
type characterized by two helically grooved rotors,
which are manufactured from forged steel. The 4 pole
motor operates at speeds up to 6000 RPM to direct
drive the male rotor, which in turn drives the female
rotor on a light film of oil.
20
OUTPUTS
(Relay Output
Board)
Solenoids
Contactors
Alarm
Pump
Compressor Heater
Run Status
Evap Heater
&
VSD
VSD Logic Board
SCR Trigger Board
Power Components
PWM (Speed Control)
MOTOR
LD10478
Refrigerant gas is injected into the void created by the
un-meshing of the five lobed male and seven lobed fe-
male rotors. Further meshing of the rotors closes the
rotor threads to the suction port and progressively com-
presses the gas in an axial direction to the discharge
port. The gas is compressed in volume and increased
in pressure before exiting at a designed volume at the
discharge end of the rotor casing. Since the intake and
discharge cycles overlap, a resulting smooth flow of
gas is maintained.
The rotors are housed in a cast iron compressor hous-
ing precision machined to provide optimal clearances
for the rotors. Contact between the male and female
rotor is primarily rolling on a contact band on each of
the rotor's pitch circle. This results in virtually no rotor
wear and increased reliability, a trademark of the screw
compressor.
The MTS compressor incorporates a complete anti-
friction bearing design for reduced power input and
increased reliability. Separated, cylindrical, roller bear-
ings handle radial loads. Angular-contact ball bearings
handle axial loads. Together they maintain accurate ro-
tor positioning at all pressure ratios, thereby minimiz-
ing leakage and maintaining efficiency.
Figure 3 - Compressor
Form 201.23-NM2
Issue date: 12/19/2023
LD10481
LD10482
Johnson Controls
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