Product specifications

11
WINDOWS
®
BASED MICROCOMPUTER CONTROLLER (CONT.)
Display Information
All information is displayed using common terms that
are easy to understand. It is a simple procedure to
determine the actual status of the system and the
individual circuits, as they are displayed in common
terms that are meaningful. The 2 line by 16 extra large
character alphanumeric liquid crystal display (LCD)
utilizes easy to understand menu-driven software. The
LCD displays eight character alphanumeric sensor
names and twelve character alphanumeric set point
names enabling the use of meaningful status names.
This enables an inexperienced operator to quickly work
through these menus to obtain the information they
require or to modify control parameters. The well
designed keypad is separated into a DISPLAY STATUS
section and an ENTR Y section each consisting of eight
keys that are clearly labeled to identify the information
that will be displayed. When data is being modified,
the second display line contains help information to
ensure that the desired modification is properly made.
Easily accessible measurements include:
•Current capacity status
•Current circuit/compressor status
•Leaving chilled water temperature
•Evaporator pressure of each refrigerant circuit
•Condenser pressure of each refrigerant circuit
•Compressor elapsed run time, each compressor
•Number of compressor starts
•Compressor contactor status
•Fan on/off status
•Remote chilled water reset input (optional)
•Water flow switch status
•External start/stop command status
•Optional low ambient temperature sensor for easier
cold ambient starting
•Optional low ambient lockout
•Optional entering fluid temperature monitoring
•Optional compressor amperage monitoring
Two proactive control features included in the
microcomputer are low suction and high discharge
pressure limiting. The second compressor in each
circuit will shutdown if the discharge pressure exceeds
the high pressure unload setpoint or if suction pressure
from either refrigerant circuit approaches the low-
pressure trip setpoint.
Capacity Control
Control is based upon leaving chilled water
temperature. How fast the temperature is changing is
calculated and capacity decisions are based upon the
rate, the current temperature, and the control
temperature zone. Capacity is never added if the system
is moving toward the temperature target at an
acceptable rate. The unit will monitor all control
functions and stage the compressors to maintain the
required operating capacity. Remote adjustment of the
leaving chilled water setpoint is accomplished through
either direct connection or a remote keypad to the
microcomputer through the RS485 long distance
differential communications port, via PC or a modem
connected to the RS232 communication port, or from
an external Building Automation System supplying a
simple 0 to 5 VDC signal.
System Control
The unit may be enabled or disabled manually, or
through the use of an external signal from a Building
Automation System. In addition, the microcomputer
may be programmed with a seven-day optional cycle
or other DB control packages may start and stop the
system through interconnecting wiring.
System Protection
The following system protection controls will
automatically act to insure system reliability:
•Low suction pressure limiting
•High discharge pressure limiting
•High motor temperature/over current
•Freeze protection
•Compressor run error
•Power loss
•Chilled water flow loss
•Sensor error
•Pump down and pumpout
•Anti-recycle
•Time delay between stages
•Load limiting via compressor current limiting