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the message below would be displayed in place of the
previous message.
When in leaving chilled liquid temperature control, the
microprocessor will attempt to control the leaving water
temperature within the temperature range of the setpoint
plus or minus the range. In the above example, control
will be in the range of 43 – 47 °F.
Return Chilled Liquid Control
S E T P O I N T
=
R A N G E
=
In return chilled liquid control, the range no longer has
a plus or minus X.X °F, but only a + X.X °F RANGE
setpoint. This indicates that the setpoint is not centered
within the RANGE but could be described as the bottom
of the control range. A listing of the limits and the
programmable values for the COOLING SETPOINTS
are shown in Table 10.
The SETPOINT and RANGE displays just described
were based on LOCAL control. If the unit was
programmed for REMOTE control (under the OPTIONS
key), the above programmed setpoints would have no
effect.
When in return chilled liquid temperature control, the
microprocessor will turn all compressors off at setpoint
and will turn compressors on as return chilled liquid
temperature rises. All compressors will be on at setpoint
plus the range. If the range equals the temperature drop
across the evaporator when fully loaded, the leaving
chilled liquid temperature will remain near the setpoint
plus or minus a few degrees as the chiller loads and
unloads according to return chilled liquid temperature.
Both LEAVING and RETURN control are described in
detail under the section on CAPACITY CONTROL.
Remote Setpoint Control
Pressing the COOLING SETPOINTS key a second
time will display the remote setpoint and cooling
range. This display automatically updates about every
2 seconds. Notice that these setpoints are not "locally"
programmable, but are controlled by a remote device
such as an ISN control, remote reset option board, or
remote PWM signal. These setpoints would only be valid
if the unit was operating in the REMOTE mode.
The following messages illustrate both leaving
chilled liquid control and return chilled liquid control
respectively.
JOHNSON CONTROLS
4 5 . 0
° F
+ 1 0 . 0 ° F
R E M
S E T P
R A N G E
=
(leaving chilled liquid control)
R E M
S E T P
R A N G E
(return chilled liquid control)
The low limit, high limit, and default values for the keys
under "SETPOINTS" are listed in Table 10.
Pressing the COOLING SETPOINTS a third time will
bring up the display that allows the Maximum EMS-
PWM Temperature Reset to be programmed. This
message is shown below.
M A X
E M S - P W M
T E M P
R E S E T
The Temp Reset value is the maximum allowable remote
reset of the temperature setpoint. The setpoint can be
reset upwards by the use of an Energy Management
System. See page 152 and 164 for a detailed explanation
of this feature.
As with the other setpoints, the ↑ (UP) arrow and ↓
(DOWN) arrow keys are used to change the Temp Reset
value. After using the ↑ (UP) and ↓ (DOWN) arrows to
adjust to the desired setpoint, the ENTER/ADV key must
be pressed to enter this number into memory.
Schedule/Advance Day Key
The SCHEDULE is a seven day daily schedule that
allows one start/stop time per day. The schedule can be
programmed Monday through Sunday with an alternate
holiday schedule available. If no start/stop times are
programmed, the unit will run on demand, providing the
chiller is not shut off on a unit or system shutdown. The
daily schedule is considered "not programmed" when
the times in the schedule are all zeros (00:00 AM).
To set the schedule, press the SCHEDULE/ADVANCE
DAY key. The display will immediately show the
following display.
M O N
S T A R T
S T O P
FORM 150.72-NM1 (1020)
=
4 4 . 0 ° F
+ / - 2 . 0 ° F
=
4 4 . 0 ° F
=
+ 1 0 . 0 ° F
R E M O T E
=
+ 2 0 ° F
=
0 0 : 0 0
A M
=
0 0 : 0 0
A M
143
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