JOHNSON CONTROLS
116
FORM 150.62-NM8 (1020)
UNIT OPERATION
SYSTEM LEAD/LAG
Lead/lag between systems may be selected to help
equalize average run hours between systems on chillers
with 2 refrigerant systems. This may be programmed
under the OPTIONS key. Auto lead/lag allows automatic
lead/lag of the two systems based on average run hours of
the compressors in each system. Manual lead/lag selects
specifically the sequence in which the
microprocessor
starts systems.
COMPRESSOR LEAD/LAG
The compressors within a system rotate starts in
sequence 1, 2 or 1, 2, 3 with wraparound. The longest‑off
compressor in a system will start first, and the longest‑
running compressor in a system will turn off first. When
unloading, the system with the most compressors ON,
unloads first. The lag system will shut down a compressor
first when equal numbers of compressors are operating
in each system. The microprocessor will not attempt to
equalize run time of compressors in a system.
Once the second system has started a compressor,
the microprocessor will attempt to equally load each
system. Once this occurs, loading will alternate between
systems.
If soft start is enabled on European models with this
option, compressor lead/lag will function as outlined
in Option 12 under the OPTIONS key.
ANTI-RECYCLE TIMER
The programmable anti-recycle timer assures that
systems do not cycle. This timer is programmable under
the PROGRAM key between 300 and 600 seconds.
Whenever possible, to reduce cycling and motor heating,
the anti-recycle timer should be adjusted to 600 seconds.
The programmable anti-recycle timer starts the timer
when the first compressor in a system starts. The timer
begins to count down. If all of the compressors in a
circuit cycle off, a compressor within the circuit will
not be permitted to start until the anti-recycle timer has
timed out. If the lead system has run for less than
five
minutes, 3 times in a row, the anti-recycle timer will be
extended to 10 minutes.
ANTI-COINCIDENCE TIMER
This timer is not present on single-system units. Two
timing controls are present in software to assure
compressors within a circuit or between systems, do not
start simultaneously. The anti-coincidence timer assures
there is at least a one minute delay between system starts
on 2-circuit systems. This timer is NOT programmable.
The load timers further assure that there is a minimum
time between compressor starts within a system.
Notes:
1. Step 1 is Hot Gas Bypass and is skipped when loading occurs. Hot Gas Bypass operation is inhibited during
pumpdown.
2. Step 3 is skipped when loading occurs.
3. Step 4 is skipped when unloading occurs.
* STEP can be viewed using the OPER DATA key and scrolling to COOLING DEMAND.
TABLE 26 – RETURN CHILLED LIQUID CONTROL FOR 4 COMPRESSORS (6 STEPS)
*STEP
COMPRESSOR
COMPRESSOR ON POINT
COMPRESSOR OFF POINT
0
0
SETPOINT
SETPOINT
1
1 W/HGB
SP + CR/8 (Note 1)
SETPOINT
2
1 NO HGB
SP + CR/4
SP + CR/8
3
2
SP + 2*CR/4 (Note 2)
SP + CR/4
4
2
SP + 2*CR/4
SP + CR/4 (Note 3)
5
3
SP + 3*CR/4
SP + 2*CR/4
6
4
SP + CR
SP + 3*CR/4
Summary of Contents for YCAL0014E Series
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