Dunham-Bush ACDS, Installation, Operation & Maintanance Manual

Page: 47 / 93

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4.0 ELECTRICAL
4.3.6.14 Sensor Alarm
If the computer measures an analog
value (temperature, pressure.) that is
far beyond normal operating values, the
associated compressors are shutdown.
The computer then stores the alarm
code corresponding to the sensor
alarm. A sensor alarm indicates a
problem in the analog measurement
system.
4.3.6.15 No-Stop Alarm
If the controller turns off a compressor,
but the compressor digital input does
not turn off, a No-Stop alarm is
generated. The computer will turn off
the control power relay which disables
all compressor control circuits and will
turn on the alarm light. This alarm
indicates a wiring or hardware error.
4.3.6.16 Low Differential Pressure Alarm
For proper lubrication, a compressor
requires a 30 psid [2.1BAR] differential
pressure between condenser and
evaporator pressures. If the differential
pressure is less than 30 psid [2.1BAR]
for 3 minutes while a compressor is
operating, all compressors will be shut
down. The controller will store the low
differential pressure alarm code and
turn on the alarm light. The ‘Reset
Alarm’ key must be pressed to clear the
alarm.
4.4 CONDENSER FAN
CONTROL LOGIC
If the differential pressure is less, the controller
provides two types of control logic for air-cooled
condensers. The type of control will be governed
by the physical condenser layout of the unit. Each
method of control is enhanced with adaptive, self-
learning, fan control logic. The end result is
condenser control that offers significantly reduced
fan cycling and improved efficiency. The two
types of air-cooled condenser control logic are
explained as follows:
1. Adaptive Individual Air-cooled Condenser
Control
This type of control is based upon a single
compressor per circuit. The individual
discharge pressure on that circuit will be the
controlling pressure.
2. Adaptive Air Combined Air-cooled
Condenser Control
This type of control is based upon a condenser
that is controlled by the highest discharge
pressure from any one of the compressors
sharing that circuit (compressor 1&2 - share;
compressor 3&4 - share). The highest
discharge pressure between the sharing
compressors will be the controlling pressure.
4.4.1 Air Cooled Condenser Control
Setpoints
The air-cooled condenser setpoints are as
follows:
Setpoint COND Stage 1 ON - Condenser stage
1 on.
Setpoint COND Stage 2 OFF - Condenser stage
2 off.
Setpoint COND DIFF ON - Differential
pressure for
additional
condenser stages.
Setpoint COND DIFF OFF - Differential
pressure for
subtracting
condenser stages.
A compressor must be operating for the
condenser fans to operate. The condenser points
(i.e. fans) will turn on based upon the value in
setpoint COND Stage 1 ON. When the discharge
pressure exceeds this value, the first condenser
point is turned on. If additional condenser points
exist, they will be turned on when the pressure
exceeds the previous cut in value (COND Stage 1
ON for the first stage) plus the value contained in
COND DIFF ON setpoint.
Condenser points (i.e. fans) will be turned off
based upon the value in the setpoint COND ST2
OFF (COND Stage 2 turn OFF point). As the
discharge pressure is reduced, the condenser
points will be turned off based upon the COND