Return Chillled Liquid System Lead/Lag And Compressor Sequencing; Table 15 - Return Chilled Liquid Control For 4 Compressors (6 Steps); Table 16 - Return Chilled Liquid Control For 4 Compressors (6 Steps) - York YLAA0285SE Manual

SECTION 8 – UNIT OPERATION
TABLE 15 – RETURN CHILLED LIQUID CONTROL FOR 4 COMPRESSORS (6 STEPS)
*STEP COMPRESSOR
0
1
2
3
4
5
6
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.
RETURN CHILLLED LIQUID SYSTEM LEAD/
LAG AND COMPRESSOR SEQUENCING
A lead/lag option may be selected to help equalize
average run hours between systems with two refrigerant
systems. This may be programmed under the OPTIONS
key. Auto Lead/Lag of the two systems based on average
run hours of the compressors in each system. Manual
Lead/Lag specifically selects the sequence in which the
microprocessor board starts the systems.
The microprocessor board will sequence compressors
load and unload systems according to Table 16. The
microprocessor will lead/lag compressors within each
circuit to maximize individual compressor run time
for the purpose of lubrication. It will also prevent the
TABLE 16 – RETURN CHILLED LIQUID CONTROL FOR 4 COMPRESSORS (6 STEPS)
Step COMP 1
0 OFF
1 ON + HG
2 ON
3 ON
4 ON
5 ON
6 ON
NOTES
1. Step is Hot Gas Bypass and is skipped when loading occurs. Hot Gas Bypass operation is inhibited during pumpdown. For Leaving Chilled
Liquid Control the Hot Gas Bypass solenoid is energized only when the lead compressor is running and the LWT < SP, the Hot Gas Bypass
solenoid is turned off when the LWT > SP + CR/2.
1. Step 1 is not used for loading or unloading.
2. Step 3 is skipped when loading occurs.
3. Step 4 is skipped when unloading occurs.
170
COMPRESSOR ON POINT
0
1 W/HGB
1 NO HGB
2
2
3
4
LEAD SYSTEM
COMP 2
OFF
OFF
OFF
OFF
ON
ON
ON
SETPOINT
SP + CR/8 (Note 1)
SP + CR/4
SP + 2*CR/4 (Note 2)
SP + 2*CR/4
SP + 3*CR/4
SP + CR
same compressor from starting two times in a row. The
microprocessor board will not attempt to equalize run
time on individual compressors within a system.
Each compressor in a system will be assigned an
arbitrary number 1 or 2. The non-running compressor
within a system with the lowest priority number will
always be the next compressor to start. The running
compressor with priority number 1 will always be the
next compressor to shut off. Whenever a compressor is
shut off, the priority numbers of all compressors in each
system will be decreased by 1 with the wrap around.
This control scheme assures the same compressor does
not repeatedly cycle on and off.
- COMP 1
-
-
See NOTE 1
-
-
See NOTE 2
-
See NOTE 3
-
-
FORM 150.72-NM3 (1020)
ISSUE DATE 10/05/2020
COMPRESSOR OFF POINT
SETPOINT
SETPOINT
SP + CR/8
SP + CR/4
SP + CR/4
SP + 2*CR/4
SP + 3*CR/4
LAG SYSTEM
COMP 2
OFF OFF
OFF OFF
OFF OFF
ON OFF
OFF OFF
ON OFF
ON ON
JOHNSON CONTROLS
(Note 3)
-
-
-
-
-
-
-
-