FORM 150.75-NM2
55
YORK INTERNATIONAL
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 0.1-20°F.
NOTE: When programming values between 0.1-9.9°F,
it is required to first key in a 0 or 00. Ex-
ample: 0.5-9°F.
The next item which will require programming is the
RATE SENSITIVITY. The RATE SENSITIVITY is a
means of overriding the leading/unloading timers when
water temperatures are in the RATE CONTROL RANGE
or the CONTROL RANGE. This allows the micro to re-
act to abrupt downward changes in leaving or return
water temperatures. The ability to respond to rate of
change variations in water temperatures gives the mi-
cro anticipation capabilities to reduce the possibility
of overshoot in leaving water temperature.
In demand limiting applications, to avoid cycling, or to
avoid overshoot, a low RATE SENSITIVITY may be
selected. This allows the micro to go into rate control to
prevent loading or cause unloading whenever water
temperatures drop faster than the programmed RATE
SENSITIVITY. Rate Control can go into effect when-
ever water temperatures are in RATE CONTROL
RANGE or the CONTROL RANGE. For these applica-
tions, a 3-5°F/min. RATE SENSITIVITY is recom-
mended. 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 selection
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 thinking
the RATE SENSITIVITY has been exceeded,
preventing loading and allowing leaving water
temperature to rise above the desired tempera-
ture.
For normal comfort cooling, or process applications,
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 as-
sure normal loading will occur at the fastest possible
speed. In most applications, 5.0°F/min. is suggested.
If unsure of a RATE SENSITIVITY selection, use
5.0°F/min.
To program the RATE SENSITIVITY, first press the
PROGRAM key. Repetitively press the ENTER key un-
til 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.
LOADING AND UNLOADING
In mixed water temperature control, loading and unload-
ing will take place as needed to keep water tempera-
ture in the CONTROL RANGE between the TARGET
and LOW LIMIT WATER TEMPERATURE. As men-
tioned earlier in this manual, the CONTROL RANGE is
the temperature range of the leaving water tempera-
ture that is acceptable to the user and has been previ-
ously programmed into memory using the CHILLED
LIQUID TEMP RANGE key.
Usually this is a window of water temperatures of about
2° - 3°F. The micro will cause loading and unloading
actions to occur as needed to keep leaving water tem-
peratures in the lower half of this range. Refer to Fig.
27 to aid in understanding the loading and unloading
scheme performed by the microprocessor.
Within the lower half of the CONTROL RANGE, the
microprocessor will not call for any further loading or
unloading unless the Rate Sensitivity is exceeded. If
temperature drop exceeds 1X the Rate Sensitivity, the
micro will unload the chiller to prevent overshoot.
If leaving water temperature should fall into the tem-
perature range BELOW THE CONTROL RANGE
which is below the programmed Low Limit WATER
TEMPERATURE, the microprocessor will unload the
chiller in 20 sec. intervals until water temperature rises
back into the CONTROL RANGE.
If temperature is in the upper half of CONTROL RANGE
or in the RATE CONTROL RANGE, the microproces-
sor will continue loading the chiller as needed in 150
sec. intervals until temperatures pass into the lower half
of the CONTROL RANGE. If the rate of drop in water
temperature exceeds 2X the programmed Rate Sensi-
tivity, no further loading or unloading will result since
RATE SENS I T I V I TY
=5.0F/MIN.
ABOVE THE RATE CONTROL RANGE
RATE CONTROL TEMP RANGE
UPPER LIMIT OF
CONTROL RANGE
CONTROL RANGE (CR) TARGET
LOW LIMIT WATER
TEMPERATURE
BELOW THE CONTROL RANGE
FIG. 27 LEAVING WATER TEMPERATURE CONTROL
To Next Page
Loading...
