Table of Contents
Advertisement
Operation
GENERAL DESCRIPTION
The units are designed to work independently, or in
conjunction with other equipment via a YORK ISN
building management system or other automated control
system. When operating, the unit controls monitor the
chilled liquid system temperature at the unit and take the
appropriate action to maintain this temperature within
desired limits. This action will involve running one or
more compressors at a suitable load step to match the
cooling effect of the refrigerating systems to the heat
load on the liquid system. The heat removed from the
chilled liquid is then rejected from the air cooled con-
denser coils.
The following sections give an overview of the operation
of the unit. For detailed information, reference should
be made to the Chiller Control Panel Programming and
Data Access Operating Instructions for the unit (pages
120 - 168).
START-UP
Check the main power supplies to the unit are 'ON', all
refrigerant service valves are open (counter-clockwise
one turn short of fully open) and chilled liquid flow has
been established (unless the unit chilled liquid pump
start control is being used, in which case just ensure
the pump supply is on). Ensure only the correct system
switches (SYS 1-2) on the microprocessor circuit board
are in the 'ON' position.
Press the 'STATUS' key on the keypad and then switch
the unit ON/OFF switch below the keypad to the ON
position.
The controller will perform a pre-check to ensure that
the daily/holiday schedule and any remote interlocks will
allow the unit to run, all safety cut-outs are satisfied and
that cooling load is required (i.e. that the chilled liquid
temperature is outside the set limits). Any problems
found by the pre-check will be displayed if present. If
no problems are present and cooling duty is required the
lead compressor will start.
The display will show the anti-coincidence timer status
for the lag compressor, followed by 'NO COOL LOAD'
until it is called to operate by the control system.
JOHNSON CONTROLS
OPERATION
NORMAL RUNNING AND CYCLING
Once the unit has been started, all operations are fully
automatic. After an initial period at minimum capacity
on the lead compressor, the control system will adjust
the unit load depending on the chilled liquid tempera-
ture and rate of temperature change. If high heat load is
present, the controller will increase the capacity of the
lead compressor and/or start-up the other compressor.
If very little heat load is present, the lead compressor
will continue at minimum capacity or may simply stop
again to avoid overcooling the liquid. If the latter is the
case, one compressor will restart automatically should
the liquid temperature rise again.
Once a compressor is running, discharge pressure rises
as refrigerant is pumped into the air cooled condenser
coils. This pressure is controlled by stages of fans to
ensure maximum unit efficiency while maintaining suf-
ficient pressure for correct operation of the condensers
and expansion valves.
When a compressor is running the controller monitors
oil pressure, motor current, and various other system
parameters such as discharge pressure, chilled liquid
temperature, etc. Should any problems occur, the control
system will immediately take appropriate action and
display the nature of the fault (Section 2, page 132).
SHUTDOWN
The unit can be stopped at any time by switching the
unit ON/OFF switch just below the keypad to the OFF
position. The compressor and oil separator heaters will
energize to prevent refrigerant condensing in the com-
pressor rotors and to prevent the compressor oil becom-
ing saturated with refrigerant. If ambient temperatures
are low, the cooler heater mats will also energize to
prevent the possibility of liquid freezing in the vessels.
The mains power to the unit should not normally be
switched OFF, even when the unit is not required to run.
If mains power must be switched OFF, (for extended
maintenance or a shutdown period), the compressor
suction, discharge and motor cooling service stop valves
should be closed (clockwise) and if there is a possibility
of liquid freezing due to low ambient temperatures, the
coolers should be drained. Valves should be opened and
power must be switched on for at least 8 Hours (36 Hours
if ambient temperature is over 86°F [30°C]) before the
unit is restarted.
FORM 201.18-NM7
45
Advertisement
Table of Contents
