FORM 150.60-NM4
YORK INTERNATIONAL
45
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 tem-
peratures 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 tem-
peratures. The ability to respond to “rate of change” varia-
tions in water temperatures gives the micro “anticipa-
tion” capabilities to reduce the possibility of “overshoot”
in leaving water temperature.
In demand limiting applications, to avoid cycling or to
avoid overshoot, RATE SENSITIVITY should be low. This
allows the micro to go into rate control to prevent loading
whenever water temperatures drop faster than the pro-
grammed RATE SENSITIVITY. Rate Control can go into
effect whenever water temperatures are in RATE CON-
TROL RANGE or the CONTROL RANGE. For these ap-
plications, a 3°-5.0°F/min. RATE SENSITIVITY is rec-
ommended. This may be needed for small water loops.
However, if problems arise where the chiller does not
load and pull temperature down, select 5.0°F/min.
NOTE: Too small of a RATE SENSITIVITY 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 micro into think-
ing the RATE SENSITIVITY has been exceeded,
preventing loading and allowing leaving water
temperature to rise above the desired tempera-
ture.
For normal comfort cooling, batch, or process applica-
tions, select a high RATE SENSITIVITY of 5.0°F/min.
Before RATE CONTROL can go into effect, the water
temperature would have to change at a very high rate to
exceed the RATE SENSITIVITY value programmed. This
will assure normal loading will occur. 5.0°F/min. also
works well in comfort cooling applications. If unsure of
a RATE SENSITIVITY selection, use 5.0.F/min.
To program the RATE SENSITIVITY, first press the PRO-
GRAM 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.
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 Mi-
croprocessor Board is programmed properly:
If this message is incorrect, see the “SELECTION OF
RETURN OR LEAVING CHILLED LIQUID CONTROL”
Section (Page 41) 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 Low-Limit Water Tempera-
ture (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 water
temperature which is acceptable in the system applica-
tion. As long as leaving water temperature stays be-
tween the low limit and midpoint of the Control Range
(CR), the Microprocessor will consider the temperature
acceptable and will not initiate any loading/unloading
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
micro will attempt to control to. The “Target” tempera-
ture is not programmable, but it is always the mid-
point 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
temperature. As mentioned before, the micro will be
satisfied with a leaving temperature between 44° - 45°F
u n l e s s t h e r a t e c o n t r o l i s e x c e e d e d . T h e
microprocessor’s rate control is designed to be less
responsive 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.
To program the Low-Limit Water Temperature (LWT)
and the Control Range (CR), press the CHILLED LIQUID
R A T E
S E N S I T I V I T Y
=
5 . 0
F / M I N
L W T =
4 4 . 0
F
C R =
4 4 . 0
T O
4 6 . 0
F
L E A V I N G
W A T E R
T E M P
C O N T R O L
