JOHNSON CONTROLS
117
SECTION 7 – UNIT CONTROLS
FORM 150.27-NM1
ISSUE DATE: 09/30/2015
7
The following messages illustrate both Leaving Chilled
Liquid Control and Return Chilled Liquid Control re-
spectively.
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
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 Man-
agement System or from the Temperature Reset Option
Board.
See
EMS-PWM Remote Temperature Reset on
Page 134 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 Re-
set 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 al-
lows 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 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 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 to 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
.
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 microprocessor will turn all compressors off at set-
point and will turn compressors on as return chilled liq-
uid temperature rises. All compressors will be ON at set-
point plus the range. If the range equals the temperature
drop across the evaporator when fully loaded, the leav-
ing chilled liquid temperature will remain near the set-
point 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
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.
