OPERATION
MAGNITUDE WMT CHILLER
DAIKIN APPLIED
34
Leaving Water Temperature (LWT) Reset
The Active Leaving Water variable shall be set to the current
Leaving Water Temperature (LWT) setpoint unless modified by
one of the reset methods below. (The current LWT setpoint is
Cool LWT as determined by the chiller mode.) The type of reset
in effect is determined by the LWT Reset Type setpoint.
Reset Type – NONE
The Active Leaving Water variable is set equal to the current LWT
setpoint.
Reset Type – RETURN
The Active Leaving Water variable is adjusted by the return water
temperature.
When the chiller mode = COOL, the Active Leaving Water
variable is reset using the following parameters:
1 .
Cool LWT setpoint
2 .
Max Reset Delta T setpoint
3 .
Start Reset Delta T setpoint
Reset is accomplished by changing the Active Leaving Water
variable from the Cool LWT setpoint to the Cool LWT setpoint
+ Max Reset Delta T setpoint when the evaporator (return –
leaving) water temperature delta varies from the Start Reset
Delta T setpoint to 0.
Reset Type – 4-20 mA
The Active Leaving Water variable is set equal to the Cool LWT
setpoint if the reset signal is less than or equal to 4 mA. It is set
equal to (Cool LWT se Max Reset Delta T setpoint) if the
reset signal equals or exceeds 20 mA. The Active Leaving Water
variable will vary linearly between these extremes if the reset
signal is between 4 mA and 20 mA. An example of this action is
; temperatures are examples only.
Figure 35:
LWT Reset (Cool Mode)
Figure 36: Settings View - Modes
Table 8: Modes Setpoints
Description
Default
Range
PW
Comments
Chiller Control and mode
Unit Enable
OFF
OFF, AUTO
O
OFF: everything is
off. AUTO: Evap
pump on, comp,
cond pump and
tower on as re-
quired to meet LWT
Control
Source
Local
(HMI)
Remote
Switch,
Local (HMI),
BAS
O
Sets control source.
See "Unit Enabling/
Disabling and
Overrides" on
Available
Modes
COOL
COOL
O
COOL
Pump Control
Evaporator
Pump
Pump
Load
Balance
None, Pump
Load Bal-
ance, Pump
#1 Only,
Pump #2
Only, Pump
#1 Primary,
Pump #2
Primary
M
Pump Load Bal-
ance - balances
hours between #1
and #2 pumps,
Pump #1 Only,
Pump #2 Only - use
only specified pump
Pump #1 Prima-
ry and Pump #2
Primary - if primary
pump fails, other
pump is used
Condenser
Pump
Pump
Load
Balance
None, Pump
Load Bal-
ance, Pump
#1 Only,
Pump #2
Only, Pump
#1 Primary,
Pump #2
Primary
M
Pump Load Bal-
ance - balances
hours between #1
and #2 pumps,
Pump #1 Only,
Pump #2 Only - use
only specified pump
Pump #1 Prima-
ry and Pump #2
Primary - if primary
pump fails, other
pump is used
Compressor
4 ma
20 ma
Cool LWT Setpoint
(44.0°F)
Max Reset Delta T
(10.0°F)
(54.0°F)
0 ma
