Dunham-Bush ACDS, Installation, Operation & Maintanance Manual

Page: 48 / 93

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4.0 ELECTRICAL
ST2 OFF setpoint, plus the value in the COND
DIFF OFF setpoint for each stage number above
stage 2. Stage 2 of condenser staging will be
turned off based upon the value in the setpoint
(COND ST2 OFF). See below for an example of
condenser staging.
4.4.2 INCREASING CONDENSER
PRESSURE
(Example of 4 stage fan cycling)
COND FAN1 ON when discharge pressure is >
230psig [15.9BAR] (COND Stage 1 ON setpoint)
COND FAN2 ON when discharge pressure is >
250psig [17.2BAR] (COND Stage 1 ON plus
1xCOND DIFF ON setpoint values)
COND FAN3 ON when discharge pressure is >
270psig [18.6BAR] (COND Stage 1 ON plus
2xCOND DIFF ON setpoint values)
COND FAN4 ON when discharge pressure is >
290psig [20.0BAR] (COND Stage 1 ON plus
3xCOND DIFF ON setpoint values)
And so on for the number of condenser fans
supplying the circuit.
4.4.3 DECREASING CONDENSER
PRESSURE
(4 fan example "continued")
COND FAN4 OFF
when discharge pressure
is < 200psig [13.8BAR] (COND Stage 2 OFF plus
2xCOND DIFF OFF setpoint values)
COND FAN3 OFF
when discharge pressure
is < 190psig [13.1BAR] (COND Stage 2 OFF plus
1xCOND DIFF OFF setpoint values)
COND FAN2 OFF
when discharge pressure
is < 180psig [12.4BAR] (COND Stage 2 OFF
setpoint value)
COND FAN1 OFF
when discharge pressure
is < 170psig [11.7BAR] (COND Stage 1 OFF
setpoint value)
4.4.3.1 Adaptive Control Logic
The controller enhances the condenser
control logic above with a unique,
adaptive, self-learning fan control logic.
These enhancement results in a control
scheme that offers reduced fan cycling
and improved efficiency. Adaptive
Control Logic automatically adjusts the
fan cut-in offset based upon the
following criteria:
1. If the last fan turned on (including
FAN 1) is cycled off in 10 minutes
or less, then a COND ON OFFSET
value will be incremented by 5 psig
[0.3BAR]. This increases the fan 1
turn on value (COND ST1 ON plus
COND ON OFFSET) which in turn
increases all of the fan turn on
settings. This process will continue
until fan cycling ceases or the
adjusted turn on point for the last
fan stage is 320 psig [22.1BAR].
This will also be a setpoint.
2. The cut-in offset (COND ON
OFFSET) will be decreased by 5
psig [0.3BAR] if the last fan to be
turned on has not cycled off within
1 hour. The offset will continue to
decrease by 5 psig [0.3BAR] every
10 minutes unless fan cycling
begins again.
The Adaptive Control Logic will only
affect the condenser fan turn on logic, it
will not affect the fan turn off logic.
4.5 Master/Slave Control
Sequence
The optional master/slave control sequence is
used to sequence multiple chillers in one
installation according to the building load demand.
It also controls the dedicated chilled water pump
or motorized valve.
Vision2020i Controller offers this feature with
minimized field wiring cost compare to
conventional method that involves lots of
hardware cost. It is carried out this control
function via the advanced DBLAN communication
bus to implement the network management for
multiple chillers lead/lag communication,
sequencing and monitoring.