System information

23
Table 12 — Set Point Determination
NOTES:
1. The ice build option is disabled when heat/cool mode is set to
Heating.
2. When the ice build option is enabled and ice build is active, the
control point is the Ice Build Set Point and the controlled water
temperature is the leaving chilled water temperature.
CONTROL POINT TEMPERATURE — Capacity control is
based on achieving and maintaining a control point tempera-
ture, which is the sum of a valid set point (from the SETPOINT
screen) and a temperature reset value. In Cooling mode, the
control point temperature is equal to the set point plus tempera-
ture reset. In Heating mode, the control point temperature is
equal to the set point minus temperature reset.
The control point can be viewed directly on the main screen
or the General Parameters menu.
TEMPERATURE RESET — Three types of chilled water or
brine reset are available and can be viewed or modified on the
Reset Configuration screen.
The default screen indicates when the chilled water reset is
active. The control point Reset on the General Parameters
screen indicates the amount of reset.
To activate a reset type, access the Reset Configuration
(RESETCFG) screen and input all configuration information
for that reset type.
Reset Type 1: 4 to 20 mA Temperature Reset
— Reset Type
1 is an automatic reset utilizing a 4 to 20 mA analog input sig-
nal provided from any external sensor, controller, or other de-
vice which is appropriately configured. For this type, Degrees
Reset At 20 mA is configured in the RESETCFG table.
Reset Type 2: Remote Temperature Reset
— Reset Type 2 is
an automatic water temperature reset based on a remote tem-
perature sensor input signal. This function can be accessed by
setting the following configurations:
1. Configure the remote temperature at which no reset oc-
curs (Remote temp  NO RESET).
2. Configure the remote temperature at which full reset oc-
curs (Remote temp  FULL RESET).
3. Enter the amount of reset (Deg Reset Water DT Full).
Reset Type 3: Controlled Water Temp Delta Reset
— Reset
Type 3 is an automatic controlled water temperature reset
based on heat exchanger temperature difference. This function
can be accessed by setting the following configurations:
1. Configure the controlled water temperature delta T at
which no reset occurs (Controlled Water DELTA T 
NO RESET).
2. Configure the controlled water temperature delta T at
which full reset occurs (Controlled Water DELTA T 
FULL RESET).
3. Enter the amount of reset (Deg Reset Water DT Full).
CAPACITY CONTROL — Capacity control provides chilled
or condenser water temperature control by modulating the po-
sition of the inlet guide vane 1, and VFD speed for variable
speed compressors.
If VFD OPTION is set to VFD and increased capacity is
needed, the control will first try to increase IGV TARGET
POSITION if it has not reached the travel limit; if the travel
limit has been reached, the control increases VFD TARGET
SPEED. If decreased capacity is needed, the control first tries
to decrease VFD TARGET SPEED if it has not reached the
minimum VFD speed; if the minimum VFD speed has been
reached, the control decreases IGV TARGET POSITION in-
stead. See Fig. 35.
From the compressor relay closed point to the end of ramp
loading, the VFD TARGET SPEED is the configured VFD
start-up speed. When the chiller is running normally, the capac-
ity control determines whether and how much to change VFD
TARGET SPEED. When the chiller is in the shut-down pro-
cess, VFD TARGET SPEED will be the minimum VFD speed.
NOTE: If the VFD option is set to NO VFD, or the compressor
relay is not closed, VFD TARGET SPEED will be 0.
The guide vane position is determined by the Capacity Con-
trol function under normal conditions and other functions in
abnormal conditions, which include capacity inhibit request or
capacity decrease request. The guide vane actuator is driven by
comparing the guide vane target position and the actual posi-
tion. The guide vane actual position can be viewed on the de-
fault screen, and ranges from zero to the guide vane travel limit
configured from the Service Configuration menu. When the
chiller is shutting down or off, the guide vane is always driven
to zero.
RAMP LOADING — The ramp loading control slows the
rate at which the compressor loads up. This control can prevent
the compressor from loading up during the short period of time
when the chiller is started and the chilled water loop has to be
brought down to CONTROL POINT (Setpoint Table). Ramp
loading helps reduce electrical demand charges by slowly
bringing the chilled water to CONTROL POINT. The total
power draw during this period remains almost unchanged.
Two methods of ramp loading are available: temperature
ramp loading and motor load ramp loading.
Temperature Ramp Loading
— Temperature ramp loading
limits the rate at which the controlled water temperature de-
creases for cooling and increases for heating during ramping by
reducing on cooling mode or increasing in heating mode the
PULLDOWN SET POINT (Maintenance Menu  Capacity)
at the configured rate, until the pulldown set point is less than
the cooling mode control point or greater than the heating
mode control point. The PULLDOWN RAMP TYPE (Config-
uration Menu  General Configuration) is configured to 0 for
temperature ramp loading.
Motor Load Ramp Loading
— Motor load ramp loading lim-
its the rate at which either the line current percentage or motor
kilowatt percentage increases by incrementing the ramp de-
mand limit at the configured rate. The PULLDOWN RAMP
TYPE (Configuration Menu  General Configuration) is con-
figured to 1 for motor load ramp loading.
If DEMAND LIMIT SOURCE (Configuration Menu 
General Configuration) is set to AMPS, then PERCENT LINE
CURRENT is used for motor load ramp loading. If DEMAND
LIMIT SOURCE is set to kW, then MOTOR PERCENT
KILOWATTS is used for motor load ramp loading.
The motor load ramp loading algorithm shall be deactivated
when the Ramp Demand Limit is greater than or equal to the
ACTIVE DEMAND LIMIT (General Parameters). It is also
deactivated when Ramp Demand Limit is greater than or equal
to 60%. There will be a one-minute delay for the compressor to
be uploaded to target load (ramping load target 60%) after
ramping load demand limit is set to 60%.
EWT
CONTROL
OPTION
HEAT/COOL MODE
COOLING HEATING
Disabled Cooling LCW Set Point Heating LCDW Set Point
Enabled Cooling ECW Set Point Heating ECDW Set Point