Circuit/Compressor Staging And Loading - Carrier AquaForce B Series Controls, Start-Up, Operation, Service And Troubleshooting Instructions

period (e.g., during the winter season). If Pump Sticking Pro-

tection (Main Menu Configuration Menu

figuration Pump Sticking Protection) is set to YES and if
the unit is off at 2:00 PM, a pump will be started once each day
for 45 seconds. If the unit has 2 pumps, Pump 1 will be started
on even days (such as day 2, 4, or 6 of the month); Pump 2 will
be started on odd days (such as day 1, 3 or 5 of the month). The
default for this option is NO.
MASTER/SLAVE CHILLER PUMP OPERATION
If the Master/Slave function is active and if the chiller is the
lag unit, then the pump will be turned on when the unit is in On
mode and if the unit active lag demand limit is greater than 1%.
Otherwise, the pump will be stopped 30 seconds after the last
compressor is turned off. However, if the lag unit pump has
been configured to run even if the unit is commanded to stop

(Main Menu Configuration Menu

Lag Unit Pump Control = 1 [Run if Unit Stops]) then the
above condition will be ignored and the lag pump will run all
the time.
CHILLED WATER FLOW SWITCH STATUS
If Flow Checked if Pump Off (Main Menu

Menu Pump Configuration
Off) is set to YES, the control will monitor the chilled water
flow switch status and will send an alarm if the pump is com-
manded off and the chilled water flow switch is closed. This
can provide the user with information about a faulty evaporator
pump contactor or a failed chilled water flow switch. This pa-
rameter should be set to NO for series flow machines. The fac-
tory default for this item is YES.
MANUAL OPERATION
The evaporator pumps can be forced ON through the CCN
when the chiller is off. This allows the unit to run with no delay
and for an unlimited length of time for flow rate calculations
when the unit is installed on site. Manual operation of the
pumps is controlled through CCN points CPUMP_1 (Main

Menu Pump Status) and CPUMP_2 (Main Menu
Pump Status (0 = OFF, 1 = ON).

Circuit/Compressor Staging and Loading

The AquaForce ® 30XV chillers with Greenspeed
employ one compressor per circuit. As a result, circuit and
compressor staging are the same. The control has several con-
trol option parameters to load the compressors. The circuit/
NOTE: After compressors are fully loaded, they will both load and unload
equally with the VFDs (variable frequency drives).

Pump Con-

Master/Slave Config

Configuration

Flow Checked if Pump
® Intelligence
Fig. 31 — Initial Compressor Loading/Unloading Method
compressor start can be configured as well as the loading of
each circuit/compressor.
CIRCUIT/COMPRESSOR STAGING
The control can be configured to decide which circuit/com-
pressor starts first. Three options for this variable are allowed:
Automatic Lead-Lag, Circuit A Leads, or Circuit B Leads. The
factory default is Automatic Lead-Lag.
The automatic lead-lag function determines which circuit/com-
pressor starts first to even the wear on the compressors. The con-
trol system determines the lead circuit to equalize the operating
time of each circuit (value weighted by the number of start-ups of
each circuit). As a result, the circuit with the lowest number of op-
erating hours always starts first. The parameter can also be config-
ured to always start a particular circuit/compressor first.
To configure this option:
DISPLAY NAME
Main Menu
Circuit Priority
Configuration Menu

Sequence
Configuration
CIRCUIT/COMPRESSOR LOADING/UNLOADING
The control uses an equal compressor loading and unloading
scheme as described below to optimize the efficiency of the unit.
At start-up, the control starts the lead compressor at the lowest
frequency and then continues to load it up by increasing fre-
quency output of the corresponding VFD. If the load reaches
65% of circuit load, then the control starts the lag compressor
at its minimum frequency. While the lag compressor starts to
load up, the lead compressor may ramp down to equalize with
lag compressor, depending on conditions. When the loading of
both compressors match, they continue to load up or load down
in unison in response to the capacity demand.
In the process of unloading, if both the compressors reach min-
imum frequency/load level, any further drop in capacity will

cause the lag compressor to switch off and the lead compressor
to ramp up until load is met again. Eventually with decrease in
load the compressor goes down to minimum frequency/load
and then shuts down. See Fig. 31 for a graphical representation
of initial system loading and unloading. (Figure 31 shows an
example of possible compressor loading for a given scenario.
Since the controls are adaptive, actual loading may vary.)
32
LINE
PATH
NO.

1 0 = Auto
1 = Ckt A Priority
General 2 = Ckt B Priority
VALUE