23
1. At power up, the Magnum does not start its algorithm until Set Point 23, POWERUP DELAY time has been
satisfi ed. (This allows the power to stabilize)
2. At startup the MAGNUM verifi es the status of the ‘NO RUN CAPACITY CONTROL STATES’. If all stsates
are satiffi
3. If any one of the ‘NO RUN CAPACITY CONTROL STATES’ is not satisfi ed, the following sequence occurs:
a. All compressors are not allowed to run. Any running compressor which has satisfi ed its minimum
run time (set point #64) will have its liquid line solenoid turned off and the evaporator pump down
and compressor turned off.
b. The AO pump continues to run for 120 seconds (Set Point #108 “PUMP DELAY”) after the last
compressor is turned off.
4. If all of the ‘NO RUN CAPACITY CONTROL STATES’ are satisfi ed, the capacity control logic is now
allowed to run to maintain the Chiller target within the control zone defi ned by:
a. Set Point #1 “CTL TNK’ (Cold Tank Targ ± High and Low Zone Values)
b. Set Point #2 “CTL ZONE+” (Hot Tank Targ ± High and Low Zone Values)
5. Once the pumps are on and the proof of fl ow is on the Capacity control logic now determines if heating,
cooling or both are required based on the set points and the current status of the compressor. It will
increase or decrease its capacity as required. This is done for both heating and cooling. If additional
capacity is added and results in ether heating or cooling reaching its target the system will switch modes as
required.
6. The Capacity control logic will increase/decrease the compressor capacity and the ‘WANTED ON verses
ACTUAL ON’ to maintain the capacity required. Capacity control logic for loading & unloading the chiller is
as follows:
a. If the MHRC temperature is above the target and the Chilled Water Rate Of Change (ROC) is not
indicating the MHRC temperature is already decreasing at a suffi cient rate, the chiller’s capacity
control logic will decrement step delay. When it reaches zero the system will increase the capacity
of the running compressor or will ask for step delay and more capacity by adding to the “Steps
Wanted On” parameter(if additional steps ae available). Once “Step Wanted On” parameter has
been increased the capacity control logic has a time delay before allowing the “Steps Wanted On”
to be increased again. The time delay is dependant on how far away the temperature is from target,
Set Points #25 “STEP SENSIT” and Set Point #26 “STEP DELAY“
b. If the ROC indicates a suffi cient decrease in MHRC Out Temperature (ROC < Set Point #27 “MAX
ROC-“) the capacity control logic stops loading and holds the current capacity.
c. If the MHRC out temperature is in the control zone, special logic functions to keep the chiller within
the control zone.
d. If the MHRC out temperature is below the control zone and if the Chilled Water Rate Of Change
(ROC) is not indicating the water temperature is already increasing at a suffi cient rate, the chiller’s
capacity control logic asks for less capacity by decrement step delay. When it reaches zero the
system will decrease the capacity of the running compressor(s) or will reduce the “Steps Wanted
On” parameter. Once “Step Wanted On” parameter has been decreased the capacity control logic
has a time delay before allowing the “Steps Wanted On” to be decreased again. The time delay is
dependant on how far away the temperature is from target, Set Points #25 “STEP SENSIT” and Set
Point #26 “STEP DELAY“.
e. If the ROC is indicating a suffi cient increase in MHRC Out Temperature (ROC < Set Point #27 “MAX
ROC-“) the capacity control logic stop unloading and holds the current capacity.
16. MHRC Sequence of Operation
ed the hot and cold pumps are started. Refer to Appendix A.
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