JOHNSON CONTROLS
145
SECTION 7 – UNIT CONTROL CENTER
FORM 150.67-NM2
ISSUE DATE: 01/31/2019
7
The following messages illustrate both leaving chilled
liquid control and return chilled liquid control respec-
tively.
R E M S E T P = 4 4 . 0 ° F
R A N G E = + / - 2 . 0 ° F
(leaving chilled liquid control)
R E M S E T P = 4 4 . 0 ° F
R A N G E = + 1 0 . 0 ° F
(return chilled liquid control)
The low limit, high limit, and default values for the
keys under “SETPOINTS” are listed in Table 12.
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 R E M O T E
T E M P R E S E T = + 2 0 ° F
The Temp Reset value is the maximum allowable re-
mote reset of the temperature setpoint. The setpoint can
be reset upwards by the use of an Energy Management
System or from the Temperature Reset Option Board.
See page 176 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 al-
ternate 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 pro-
grammed” 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 fol-
lowing display.
M O N S T A R T = 0 0 : 0 0 A M
S T O P = 0 0 : 0 0 A M
Notice that the RANGE was programmed for +/- X.X°
F. This indicates the SETPOINT to be in the center of
the control range. If the control mode has been pro-
grammed for RETURN LIQUID control, the message
below would be displayed in place of the previous
message.
When in leaving chilled liquid temperature control, the
micro will attempt to control the leaving water tem-
perature within the temperature range of the setpoint +
or – 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 = 4 5 . 0 ° F
R A N G E = + 1 0 . 0 ° F
In return chilled liquid control, the range no longer has
a +/- 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 pro-
grammable values for the COOLING SETPOINTS are
shown in Table 12.
The SETPOINT and RANGE displays just described
were based on LOCAL control. If the unit was pro-
grammed for REMOTE control (under the OPTIONS
key), the above programmed setpoints would have no
effect.
When in return chilled liquid temperature control, the
micro will turn all compressors off at setpoint and will
turn compressors on as return chilled liquid tempera-
ture rises. All compressors will be on at setpoint + 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 + or
– a few degrees as the chiller loads and unloads accord-
ing 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.
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