YORK INTERNATIONAL
44
PROGRAMMING LEAVING WATER CONTROL
Chilled Liquid Temp/Range
When the CHILLED LIQUID TEMP/RANGE key is
pressed, the following message will be displayed for 3
seconds indicating Dip Switch S1, Switch #4 on the
Microprocessor Board is programmed properly:
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 and
hold:
This message will display the Low-Limit Water Tem-
perature (LWT) and the Control Range (CR). In the
sample above, the LWT is 44.0°F and the CR is 44° -
46°F.
The Control Range (CR) is the variation in leaving wa-
ter temperature which is acceptable in the system
application. As long as leaving water temperature stays
between the low limit and midpoint of the Control Range
(CR), the Microprocessor will consider the tempera-
ture acceptable and will not initiate any loading/unload-
ing reaction unless Rate Control requires. The
Low-Limit Water Temperature (LWT) is the minimum
acceptable leaving water temperature in the Control
Range (CR), not the actual user desired leaving water
temperature setpoint.
The desired leaving water temperature is known as the
Target temperature which is the temperature the mi-
cro will attempt to control too. The Target tempera-
ture is not programmable, but it is always the midpoint
of the Control Range (CR). Example: A control range
of 44° - 46°F will have a Target Temp of 45°F, which
should equal the desired system leaving water tem-
perature. As mentioned before, the micro will be satis-
fied with a leaving temperature between 44° - 45°F
unless the rate control is exceeded. The micro-
processors rate control is designed to be less respon-
sive in the upper half of the Control Range (i.e. 45° -
46°F) than in the lower half (i.e. 44° - 45°F). This is to
prevent overshoot.
The next item which will require programming is the
RATE SENSITIVITY. The RATE SENSITIVITY is a
means of overriding the loading/unloading timers
when water temperatures are in the RATE CONTROL
RANGE or the CONTROL RANGE. This allows the
micro to react to abrupt downward changes in leaving
or return water temperatures. The ability to respond to
rate of change variations in water temperatures gives
the micro anticipation capabilities to reduce the possi-
bility of overshoot in leaving water temperature.
In demand limiting applications, to avoid cycling or to
avoid overshoot, a low RATE SENSITIVITY may be se-
lected. This allows the micro to go into rate control to
prevent loading whenever water temperatures drop
faster than the programmed RATE SENSITIVITY. Rate
Control can go into effect whenever water tempera-
tures are in RATE CONTROL RANGE or the CONTROL
RANGE. For these applications, a 3°-5°F/min. RATE
SENSITIVITY is recommended. This may be needed
for small water loops. However, if problems arise where
the chiller does not load and pull temperature down,
select 5°F/min.
NOTE: Too small of a RATE SENSlTlVlTY value se-
lection may prevent loading due to varying
flows or if the water system allows a slug of
cold water to enter which falsely fools the mi-
cro into thinking the RATE SENSlTlVlTY has
been exceeded, preventing loading and allow-
ing leaving water temperature to rise above the
desired temperature.
For normal comfort cooling, batch, or process applica-
tions, select a high RATE SENSITIVITY of 5°F/min. Be-
fore RATE CONTROL can go into effect, the water tem-
perature would have to change at a very high rate to
exceed the RATE SENSITIVITY value programmed.
This will assure normal loading will occur. 5°F/min. also
works well in comfort cooling applications.
If unsure
of a RATE SENSITIVITY selection, use 5°F/min.
To program the RATE SENSITIVITY, first press the
PROGRAM key. Repetitively press the ENTER key until
the display below appears.
Key in the desired value and press the ENTER key. The
new value will be entered into memory and the display
will advance to the next user programmable limit.
The micro will accept a range of programmable values
between 0.5° - 5.0°F/min.
R A T E
S E N S I T I V I T Y
=
5 . 0
F / M I N .
L E A V I N G
W A T E R
T E M P
C O N T R O L
L W T =
4 4 . 0
F
C R =
4 4 . 0
F
T O
4 6 . 0
F