York YCAZ33BA3, Руководство пользователя, Страница: 42 / 88

YORK INTERNATIONAL
42
After the Design Leaving Water Temperature (LWT) is
keyed in, the lower limit of the CR (Control Range) in
the display message will automatically change to a
value identical to the “LWT”. See below:
The cursor will advance to the final entry which is
the upper limit of the CR (Control Range). This value
must be programmed to equal the design LWT plus
the CR differential (
D
T across the evaporator fully
loaded). In the above examples it would be 44.0 +
10.0 = 54.0°F.
Key in the upper limit of the CR and press ENTER.
Otherwise the new values will not be entered into mem-
ory. After pressing the ENTER key, the display will con-
tinue to show the LWT and Control Range message
until another key is pressed.
The micro will accept a range of programmable LWT
values from 10.0 - 70.0°F (See “SWITCH 1”, Page 28).
It will also accept a value for the upper limit of the CR
of 4 - 20°F above the LWT Setpoint.
If brine or glycol is used in the system, chilled liquid
temperatures below 40°F may be desired. To program
setpoints below 40°F, Dip Switch S1, Switch #1 on the
Microprocessor Board must be properly programmed.
(See Page 27, Fig. 12). If the switch is incorrect, when
setpoints below 40°F are entered as well as when un-
acceptable values are entered, the following message
will be displayed.
Loading/Unloading is limited by a 30 sec. Ioading/un-
loading timer between stages, with loading/unloading
occurring according to the difference between return
water temperature and the LWT Setpoint. However, on
start-up, loading will be limited to a maximum of 1 stage
per minute for the first 3 minutes. The 30 sec. Ioading
timer may also be overridden by the micro if tempera-
ture is in the Rate Control Range or the Control Range
(CR).
If this message is incorrect, see the “SELECTION OF
RETURN OR LEAVING CHILLED LIQUID CONTROL”
section (Page 40) for instructions to reprogram the Mi-
croprocessor Dip Switch S1, Switch #4.
The display will then scroll to a second message & hold:
This message will display the user’s “Design Leaving
Water Temperature” (LWT) setpoint (44.0°F in the sam-
ple above). Even though return water temperature con-
trol is being utilized, the object is to provide constant
design leaving water temperature. It is the “Design
Leaving Water Temperature” setpoint (LWT) which must
be programmed into the microprocessor.
Also included in this message is the “CONTROL
RANGE” (CR). The “CONTROL RANGE” is the tem-
perature range which loading/unloading will take place.
The lower limit of the CONTROL RANGE is always
equal to the setpoint and automatically appears when
the setpoint is keyed in. The upper limit of the CR must
be programmed.
In the above sample message, with a “CR = 44.0 to
54.0°F”, the chiller will be completely off at a return
water temperature of 44.0°F and fully loaded at a re-
turn water temperature of 54.0°F. Partial loading will
occur in equal temperature intervals between 44° and
54°. Unloading will occur as return temperature drops
below 54°F with the chiller cycling completely off at 44°F.
These temperatures provide a Control Range differen-
tial of 54.0 – 44.0 = 10.0°F.
Once the upper limit of the CR is programmed, the “CON-
TROL RANGE” (CR) differential Must Always equal the
actual water temperature drop (
D
T) across the evapora-
tor with the chiller completely loaded. Keep this in mind
when programming the high end of the CR. In many
cases, due to improper flows, actual temperature drop
occurs across the evaporator (
D
T) will not equal design.
For proper operation, adjust flow as needed or program
the “CONTROL RANGE” as needed. However accom-
plished, the “CONTROL RANGE” differential Must equal
the evaporator temperature drop when fully loaded or
leaving water temperatures well above or well below the
desired setpoint will result.
To program the Chilled Liquid Setpoints, press the
CHILLED LIQUID TEMP/RANGE key. The display will
first exhibit a message that “RETURN WATER TEMP
CONTROL” is selected and 3 seconds later automat-
ically scroll to the next display of LWT and CR. The
cursor will stop at the first digit of LWT. Key in the “De-
sign Leaving Water Temperature” (LWT) that is required
in the system. See the following:
L W T = 4 4 . 0 F
C R = 4 4 . 0 T O 5 4 . 0 F
L W T = 4 4 . 0 F
C R = 4 4 . 0 T O 5 4 . 0 F
Design Leaving Water Temperature
L W T = 4 4 . 0 F
C R = 4 4 . 0 T O 5 4 . 0 F
The lower limit of the CR will always
automatically equal LWT
O U T O F R A N G E
T R Y A G A I N !