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Sequence of Operations
This manual describes a typical air-cooled chiller
system with few, if any, optional components or
devices attached. To cover the primary difference in
construction and operation, two sequences of
operation are included; one for a constant flow chiller
system and the other for a variable flow chiller system.
Constant Flow Sequence
1. The chiller operates with high voltage power
supplied to the unit at all times.
2. When there is power on the system, the primary
microprocessor controller selects a new lead
module and rotates this lead once every 168 hours,
or once a week.
3. The chiller system is enabled when the system on/
off switch on the remote interface panel is
energized, and the remote start/stop relay is
enabled, either through a contact closure or via the
BMS.
4. Once flow is established and the system demand
(based on leaving water temperature) indicates that
there is a requirement for cooling, the lead
compressor of the lead module will energize
provided all safeties on that circuit are satisfied.
5. As the system demand increases, the first
compressor of the first secondary module will
energize provided all safeties on that circuit are
satisfied.
6. As the system demand increases, the leaving water
temperature from the chiller will slowly increase
until the differential set point is reached (set point
plus 4 °F [2 °C]). When the differential is reached, a
third compressor from the second secondary
module (or if there is only one secondary module,
the second compressor of the lead module) will be
brought on-line.
7. As the demand continues to increase, and the
temperature once again reaches the set point plus
differential setting, a fourth compressor from the
third secondary module (or the second compressor
of the first secondary if there is only one secondary)
will be brought on line.
8. On a decrease in system demand such that the
leaving water temperature reaches the set point
minus the differential (set point minus 1 °F (0.5 °C)),
a compressor will de-energize in the reverse of the
sequence by which it came on.
9. This process occurs throughout the operating range
of the chiller.
10. The microprocessor will rotate to designate a new
lead module once a week to equalize the run time
among the modules.
ARTC-SVX001B-EN
11. If power is removed and then returned to a chiller
system (i.e. power failure), the compressors will
restart every five seconds for the next five minutes
as needed. In a power return restart, once all the
compressors have restarted every five seconds as
needed within five minutes, any subsequent cycling
of compressors will be every five minutes.
12. When a redundant primary microprocessor
controller is provided on a chiller module, the
redundant primary microprocessor will, without
downtime and without any operational deficiency,
perform the primary microprocessor functions
should it fail. All operational sequences will be
uninterrupted and uninhibited should the primary
microprocessor fail.
Variable Flow Sequence: No
Tank and Pump Module
1. The chiller is designed to operate with high voltage
power supplied to the unit at all times.
2. When there is power on the system, the primary
microprocessor selects the lead chiller module and
rotates this lead once every 168 hours week. The
lead module's electronic isolation valve will initially
be provided with full power input driving the valve
fully open.
3. The chiller system is enabled when the system on/
off switch on the remote interface panel is
energized, and the remote start/stop relay is
enabled either through a contact closure or via the
BMS.
4. The variable frequency drives (VFDs) for the
customer-provided system pumps must monitor
the system pressure differential to determine the
pumps' speed. The electronic modulating valves on
the modules open and close based on chiller
system leaving fluid temperature. The system
pump VFDs operate independently from the chiller
modules; an increase in flow from the pumps
corresponds to a higher system leaving fluid
temperature and a demand for cooling. Electronic
modulating valves open on a chiller module and its
compressors turn on to satisfy the cooling demand.
A decrease in flow, as determined by the system
pressure differential, lowers the system leaving
fluid temperature, decreases the demand for
cooling and the chiller modules shut down and
their electronic valves close.
5. The electronic isolation valve of the primary lead
chiller identified in step 2 is already energized.
Therefore, the system pump must produce the
minimum flow required by the lead chiller. A
system bypass must be provided by the customer
and installed external of the chiller to assure that
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