Quantech QTC3040T, Installation Operation & Maintenance

Page: 129 / 190

129
QUANTECH
FORM QTC3-NM1
ISSUE DATE 08/03/2022
SECTION 7 – UNIT CONTROLS
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 21 on
page 159 .
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 Op-
tion Board. See Remote BAS/EMS Temperature Reset
Using a Voltage or Current Signal on page 167 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.
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
water temperature within the temperature range of the
se 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 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 21 on page 159 .
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
liquid temperature rises. All compressors will be on at
setpoint 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 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
Capacity Control on page 157
.
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 s. Notice that these setpoints are not “locally” pro-
grammable, 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.