Specifications
36
Ramp Loading — Ramp Loading limits the rate of
change of the leaving fluid temperature. If the unit is in a Cool-
ing mode and configured for Ramp Loading Select (Ramp
Loading Select, RL.S), the control makes two comparisons
before deciding to increase capacity. First, the control calcu-
lates the temperature difference between the control point and
leaving fluid temperature. If the difference is greater than 4° F
(2.2° C) and the rate of change (°F or °C per minute) is more
than the configured Cool Ramp Loading rate (Cooling Ramp
Loading, CRMP), then the control does not allow any increase
of capacity.
To configure this option with the Touch Pilot™ display:
To configure this option with the Navigator™ display:
Temperature Reset — Temperature reset is a value
added to the basic leaving fluid temperature set point and the
resulting sum of these values is the new control point. When a
non-zero temperature reset is applied, the chiller controls to the
new control point, not the set point. The type of temperature re-
set is configured with the Cooling Reset Type (Cooling Reset
Select, CRST) variable. Types of temperature reset are avail-
able: Return Water Reset, Space Temperature Reset, and 4-20
mA Temperature Reset.
Under normal operation, the chiller will maintain a constant
entering or leaving fluid temperature, based on the configura-
tion, approximately equal to the chilled fluid set point. As the
cooler load varies, the cooler fluid temperature difference will
change in proportion to the load. For example, if the chiller was
selected for a Entering to Leaving Water Temperature
difference of 10 F (5.5 C) at full load, at 50% load the tempera-
ture difference would be 5 F (2.2 C). See Fig. 19. Because the
change in temperature through the cooler is a measure of the
building load, the temperature difference reset is the average
building load. Usually the chiller size and fluid temperature set
point are selected based on a full-load condition. At part load,
the fluid temperature set point may be lower than required. If
the fluid temperature were allowed to increase at part load, the
efficiency of the machine would increase. The chiller can also
be set for return water temperature control. See Fig. 20.
Other indirect means of estimating building load and con-
trolling temperature reset are also available and are discussed
below.
To verify that reset is functioning correctly, subtract the Set-
point Select (Current Setpoint, SETP) from the Control Point
(Control Point, CTPT) to determine the degrees reset.
RETURN WATER RESET — The control system is capable
of performing fluid temperature reset based on cooler fluid
temperature difference. Because the change in temperature
through the cooler is a measure of the building load, the tem-
perature difference reset is, in effect, an average building load
reset method.
Return Water Temperature Reset allows for the chilled
water temperature set point to be reset upward as a function of
the fluid temperature difference (building load).
NOTE: Return Water Temperature Reset should not be used
with variable cooler flow rate systems.
To use Return Water Temperature Reset, four variables
must be configured. Cooling Reset Type (Cooling Reset
Select, CRST) must be enabled. The variable Delta T No Reset
Temp (Delta T No Reset Value, CRT1) should be set to the
cooler temperature difference (T) where no chilled water tem-
perature reset should occur. The variable Delta T Full Reset
Temp (Delta T Full Reset Value, CRT2) should be set to the
cooler temperature difference where the maximum chilled
water temperature reset should occur. The variable Degrees
Cool Reset (Cooling Reset Deg. Value, DGRC) should be set
to the maximum amount of reset desired.
To configure this option with the Touch Pilot™ display:
To configure this option with the Navigator™ display:
In the example in Fig. 21 using Return Water Temperature
Reset, the chilled water temperature will be reset by 5° F
(2.8° C) when the Fluid Temperature Difference is 2° F
(1.1° C) and 0° F (0° C) reset when the Temperature Difference
is 10° F.
SPACE TEMPERATURE RESET — The control system is
also capable of temperature reset based on space temperature
(SPT). An accessory sensor must be used for SPT reset
(33ZCT55SPT). The Energy Management Module (EMM) is
also required for temperature reset using space temperature.
To use Space Temperature Reset, four variables must be
configured. Cooling Reset Type (Cooling Reset Select, CRST)
must be enabled. The space temperature at which no tempera-
ture reset is required, Space T No Reset Temp (Space T No
Reset Value, CRS1) must be set. The space temperature at
which full temperature reset is required, Space T Full Reset
Temp (Space T Full Reset Value, CRS2) must be set. Finally,
the amount of temperature reset desired, Degrees Cool Reset
(Cooling Reset Deg. Value, DRGC), must be set.
To configure this option with the Touch Pilot™ display:
DISPLAY NAME PATH LINE NO. VALUE
Ramp Loading
Select
Main Menu
Config USER
5Yes
Cooling Ramp
Loading
Main Menu
Setpoint
14
Range: 0.2 to 2.0 °F
(0.1 to 1.1 °C)
Default: 1.0 °F (0.5 °C)
ITEM
ITEM
EXPANSION
PATH VALUE
RL.S
Ramp Load
Select
Configuration OPTN Yes
CRMP
Cool Ramp
Loading
Setpoints COOL
Range: 0.2 to 2.0 °F
(0.1 to 1.1 °C)
Default: 1.0 °F (0.5 °C)
DISPLAY NAME PATH LINE NO. VALUE
Cooling Reset
Select
Main
Menu Config USER
19
Default =0
(No Reset)
2 (Delta T)
Delta T No
Reset Value
Main
Menu Setpoint SETPOINT
7
Default =
0 F (0 C)
Delta T Full
Reset Value
Main
Menu Setpoint SETPOINT
8
Default =
0 F (0 C)
Cooling Reset
Deg. Value
Main
Menu Setpoint SETPOINT
13
Default =
0 F (0 C)
ITEM ITEM EXPANSION PATH VALUE
CRST
Cooling Reset
Typ e
Configuration RSET
Default =
No Reset
Delta T Temp
CRT1
Delta T No
Reset Temp
Setpoints COOL
Default =
0 F (0 C)
CRT2
Delta T Full
Reset Temp
Setpoints COOL
Default =
0 F (0 C)
DGRC
Degrees Cool
Reset
Setpoints COOL
Default =
0 F (0 C)
DISPLAY NAME PATH
LINE
NO.
VALUE
Cooling Reset
Select
Main Menu
Config USER
19
Default =0
(No Reset)
4 (Space Temp)
Space T No
Reset Value
Main Menu
Setpoint SETPOINT
11
Default =
14 F (–10 C)
Space T Full
Reset Value
Main Menu
Setpoint SETPOINT
12
Default =
14 F (–10 C)
Cooling Reset
Deg. Value
Main Menu
Setpoint SETPOINT
13
Default =
0 F (0 C)