Specifications

53
SETPOINT (from the SETPOINT screen) and a Water/Brine
Reset value, if any. CONTROL POINT is limited to a minimum
of 35 F (+1.7 C) for water, or 10 F (–12.2 C) for brine. Three
types of chilled water or brine reset are available and can be
viewed or modified on the TEMP_CTL screen, which is ac-
cessed from the EQUIPMENT SERVICE table.
The ICVC default screen indicates when the chilled water
reset is active. TEMPERATURE RESET on the MAINSTAT
screen indicates the amount of reset. The CONTROL POINT
will be determined by adding the TEMPERATURE RESET to
the SETPOINT.
To activate a reset type, access the TEMP_CTL screen and
input all configuration information for that reset type. Then, in-
put the reset type number (1, 2, or 3) in the SELECT/ENABLE
RESET TYPE input line.
RESET TYPE 1: 4 to 20 mA (1 to 5 vdc) TEMPERATURE
RESET – Reset Type 1 is an “automatic” reset utilizing a 4 to
20 mA or 1 to 5 vdc analog input signal provided from any
external sensor, controller, or other device which is appropri-
ately configured. Reset Type 1 permits up to ±30° F (±16.7° C)
of reset to the chilled water set point. Inputs are wired to termi-
nals J5-3 (–) and J5-4 (+) on the CCM (for 4 to 20 mA input).
In order to utilize a 1 to 5 vdc input, a 25-ohm resistor must be
wired in series with the + input lead (J5-4). For either input
type, SW2 DIP switch 2 should be set in the ON (up) position.
Inputs equivalent to less than 4 mA result in no reset, and
inputs exceeding 20 mA are treated as 20 mA.
RESET TYPE 2: REMOTE TEMPERATURE RESET —
Reset Type 2 is an automatic chilled water temperature reset
based on a remote temperature sensor input signal. Reset Type
2 permits ± 30 F (± 16 C) of automatic reset to the set point
based on a temperature sensor wired to the CCM module (see
wiring diagrams or certified drawings). The temperature sensor
must be wired to terminal J4-13 and J4-14. To configure Reset
Type 2, enter the temperature of the remote sensor at the point
where no temperature reset will occur (REMOTE TEMP –>
NO RESET). Next, enter the temperature at which the full
amount of reset will occur (REMOTE TEMP –> FULL
RESET). Then, enter the maximum amount of reset required to
operate the chiller (DEGREES RESET). Reset Type 2 can now
be activated.
RESET TYPE 3 — Reset Type 3 is an automatic chilled water
temperature reset based on cooler temperature difference.
Reset Type 3 adds ± 30 F (± 16 C) based on the temperature
difference between the entering and leaving chilled water
temperature.
To configure Reset Type 3, enter the chilled water tempera-
ture difference (the difference between entering and leaving
chilled water) at which no temperature reset occurs (CHW
DELTA T –> NO RESET). This chilled water temperature dif-
ference is usually the full design load temperature difference.
Next, enter the difference in chilled water temperature at which
the full amount of reset occurs (CHW DELTA T –> FULL RE-
SET). Finally, enter the amount of reset (DEGREES RESET).
Reset Type 3 can now be activated.
Demand Limit Control Option — The demand limit
control option (20 mA DEMAND LIMIT OPT) is externally
controlled by a 4 to 20 mA or 1 to 5 vdc signal from an energy
management system (EMS). The option is set up on the
RAMP_DEM screen. When enabled, 4 mA is the 100% de-
mand set point with an operator-configured minimum demand
at a 20 mA set point (DEMAND LIMIT AT 20 mA).
The auto. demand limit is hardwired to terminals J5-1 (–)
and J5-2 (+) on the CCM. Switch setting number 3 on SW2
will determine the type of input signal. With the switch set at
the ON position the input is configured for an externally pow-
ered 4 to 20 mA signal. With the switch in the OFF position the
input is configured for an external 1 to 5 vdc signal. In order to
use a 1 to 5 vdc input instead of 4 to 20 mA, install a 25-ohm
resistor in series with the + lead at terminal J5-2.
Surge Prevention — Constant Flow and Vari-
able Primary Flow (VPF) —
A surge condition occurs
when the lift becomes so high that the gas flow across the im-
peller reverses. This condition can eventually cause chiller
damage. The surge prevention algorithm notifies the operator
that chiller operating conditions are marginal and to take action
to help prevent chiller damage such as lowering entering con-
denser water temperature.
The surge prevention algorithm is an operator-configurable
feature that can determine if lift conditions are too high for the
compressor and then take corrective action. Lift is defined as
the difference between the saturated temperature at the impeller
eye and at the impeller discharge. The maximum lift a particu-
lar impeller wheel can perform varies with the gas flow across
the impeller and the size of the wheel.
There are two possible surge prevention methods used in
the 19XR PIC II chiller. Prior to April 2010, on machines with
software version 8 or lower, Chilled Water T compared to
Cooler-Condenser P was compared to a configured surge
line. Originally the line was straight and configured with two
points. More recently the line was configured with four points.
This method was designed around constant flow chilled water
systems.
From April 2010 (serial number 1410Qxxxxx) and later,
and in machines converted to software version 9 or higher, the
Surge Prevention algorithm has been changed to eliminate the
measurement of Chilled Water T in order to accommodate
Variable Primary Flow (VPF) chilled water systems.
Variable Flow Surge prevention is the current standard for
both constant and variable primary flow chilled water systems.
Variable Primary Flow Surge Prevention does not require a
measurement of COOLER DELTA T and is thus unaffected by
changes in flow. With Variable Primary Flow Surge Preven-
tion there is no difference in field configuration between con-
stant and variable flow water systems.
In both surge prevention methods the controls calculate the
conditions at which the compressor will surge based on operat-
ing conditions and configured values entered into the
OPTIONS screen.
The configurations as used by the controls would plot out
on a graph as a curved or stepped line. If the present operating
conditions plot at or above this line, surge prevention is turned
on.
The way in which surge prevention functions will differ
with the presence or absence of hot gas bypass and variable
speed drive.
SURGE PREVENTION ALGORITHM — The surge pre-
vention algorithm first determines if corrective action is neces-
sary. The algorithm checks 4 sets of operator-configured data
points, MIN LOAD POINT (T1/P1), the LOW LOAD POINT
(T2/P2), the MID LOAD POINT (T3/P3) and the FULL LOAD
POINT (T4/P4). These surge characteristics are factory set
based on the original selection, with the values printed on a la-
bel affixed to the bottom interior face of the control panel.
The surge prevention algorithm function and settings are
graphically displayed in Fig. 25. The four sets of load points
on the graph (sample settings are shown) describe a line the al-
gorithm uses to determine the maximum lift of the compressor.
When the actual differential pressure between the cooler and
condenser and the temperature difference between the entering
and leaving chilled water are above the line on the graph (as
defined by the minimum and full load points), the algorithm
goes into a surge prevention mode. If the actual values are be-
low the line and outside of the deadband region, the algorithm
takes no action. When the point defined by the ACTIVE DEL-
TA P and ACTIVE DELTA T, moves from the region where