JOHNSON CONTROLS
124
FORM 150.72-ICOM7
ISSUE DATE: 10/22/2020
SECTION 7 – UNIT CONTROLS
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 “SET POINTS” are listed in Table 24 on
page 157.
Pressing the COOLING SET POINTS 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 set point. The set point
can be reset upwards by the use of an Energy Man-
agement System or from the Temperature Reset Op-
tion Board. See Remote BAS/EMS Temperature Reset
Using a Voltage or Current Signal on page 165 for a
detailed explanation of this feature.
As with the other set points, 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 set point, 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.
ter of the control range. If the control mode has been
programmed for RETURN LIQUID control, the mes-
sage 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 wa-
ter temperature within the temperature range of the set
point + or – the range. In the above example, control
will be in the range of 43°F 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 set point.
This indicates that the set point 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 SET POINTS
are shown in Table 24 on page 157.
The SET POINT 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 set points 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
liquid temperature rises. All compressors will be on at
set point plus the range. If the range equals the tem-
perature drop across the evaporator when fully loaded,
the leaving 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 Capacity Control on page 155.
Remote Set Point Control
Pressing the COOLING SET POINTS key a second
time will display the remote set point and cooling
range. This display automatically updates about every
2 seconds. Notice that these set points 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 set points would only be
valid if the unit was operating in the REMOTE mode.
To Next Page
Loading...