Jetson FWCD Series, Installation Operation & Maintenance, Page: 67 / 96

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67
Standard Capacity Control
Standard capacity control on the FWCD Series
chillers is accomplished by staging the scroll
compressors on and off. The unit controller
will maintain a set point leaving chilled water
temperature within a control zone using
proportional, integral derivative (PID) logic. If
the leaving chilled water temperature starts to
decrease and falls below the set point, the unit
controller will turn one stage off. A further
reduction in temperature will result in a second
stage being turned off. The reverse is true as
the
leaving chilled water temperature
increases. Lead/lag logic is used to even the
run time on the individual compressors.
Optional Capacity Control
Chilled water temperature reset can be
accomplished in two ways. In buildings with a
building management system, the FWCD
Series unit controller allows the BMS to
communicate an offset to the chilled water
temperature set point. If a BMS is not being
used, the unit controller can accept a field
provided 0 to 5 VDC analog input signal. As
the input voltage varies away from center
(2.5V), the chilled water temperature set point
will be offset proportionally.
Note: This control logic is factory-installed
and must be denoted at the time of ordering.
Demand limiting
is a form of capacity control
that limits the number of capacity steps the
compact chiller is allowed to operate. It can be
accomplished in the same two ways as the
chilled water temperature reset: through BMS
or field-provided 0 to 5 VDC input signal.
Note: This control logic is factory-installed
and must be denoted at the time of ordering.
Array Control
The array controller option allows the FWCD
Series chiller to be an ideal solution for
facilities with growing occupancy and
structural expansion plans because chillers can
be added as capacity needs increase or
applications where convenient redundancy is
needed.
FWCD Series water-cooled chiller arrays can
be controlled by two different array controller
configurations, depending on the needs of the
application. Both options allow the array to be
controlled and operated like a single, higher
capacity,
multistage chiller. Capacity
modulation and equalization of compressor run
time is managed by the array controller. The
array controller uses the same standard
capacity control logic as an individual FWCD
unit controller but with more stages of
capacity.
Supervisory Array Controller
This option allows up to ten (10) FWCD Series
chillers to be controlled and operated. The
Supervisory Array Controller requires each
module have an individual unit controller. This
option is beneficial in applications requiring
seven (7) or more modules to be controlled and
in applications where chiller uptime is critical.
Power (115VAC) must be provided to a circuit
breaker
inside the Supervisory Array
Controller enclosure panel to power the
Supervisory
Array Controller. The
Supervisory Array Controller
enclosure also contains a field connection
terminal strip and door-mounted off/auto
switch, run indicator light and alarm indicator
light.
The Supervisory Array Controller is accessed
in the same manner as the unit controller,
through the keypad display or PC/laptop. If
communication between the individual FWCD
Series chiller unit controller(s) and the
Supervisory Array Controller is lost, or the
Supervisory Array Controller fails, the
individual FWCD Series chillers can be shifted
into manual mode to operate independent from