York Millennium YCAJ150, Установка, эксплуатация и обслуживание, Страница: 53 / 116

FORM 150.65-NM4
53 YORK INTERNATIONAL
water temperature drops into the CONTROL RANGE.
This may be required for small water loops. However, if
problems arise where the chiller does not load and pull
temperature down, select 0.1°F (0.05°C).
To program the RATE CONTROL TEMP, 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 0.1 - 20°F (0.05 - 11.1°C).
NOTE: When programming values between 0.1 - 9.9°
(0.05 - 11.1°C), it is required to first key in a “0 “
or “00”. Example: 05.9°.
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°F/min (1.7 - 2.8°C/min) RATE SENSI-
TIVITY is recommended. This may be required for small
water loops. However, if problems arise where the chiller
does not load and pull temperature down, select 5°F/
min (2.8°C/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 tem-
perature to rise above the desired temperature.
In some cases, unloading or compressor shut-
down my result.
For normal comfort cooling, batch, or process applica-
tions, select a high RATE SENSITIVITY of 5°F/min (2.8°C/
R A T E C O N T R O L T E M P
= 1 0 . 0 F
The RATE CONTROL TEMP establishes a temperature
range (0.1 - 20°F [.05 - 11.1°C]) above the “Upper Limit
of CONTROL RANGE” where the micro will limit loading
or unload the system if the rate of change of water tem-
perature reduction exceeds the programmed RATE SEN-
SITIVITY. In Fig. 14, a RATE CONTROL TEMP of 10°F
(5.5°C) is used.
In the CONTROL RANGE and RATE CONTROL RANGE
loading/unloading will normally occur according to devia-
tion from setpoint. “Rate Control” will function to prevent
loading if the water temperature change (leaving or re-
turn) exceeds the RATE SENSITIVITY, even though de-
viation from setpoint requires loading. This will reduce
the chance of overshoot.
Above THE RATE CONTROL TEMP RANGE the micro
will attempt to load the chiller every 60 seconds per stage.
This allows the chiller to gain control of the water tem-
perature as quickly as possible while still avoiding over-
shoot and limiting pulldown demand as temperature drops
and rate control is implemented.
Since RWT Control utilizes the buffering of the water
loop and a wide control (loading/unloading) range, com-
pressor/loader cycling is reduced, wear and tear on me-
chanical parts is reduced, and pulldown demand is au-
tomatically limited. This makes the selection of RATE
CONTROL TEMP and RATE SENSITIVITY values less
critical unless short water loops are encountered.
Before programming the RATE CONTROL TEMP, the user
should first determine if typically the normal fastest al-
lowable pulldowns are required or whether pulldown de-
mand limiting is desired. Programmable values from 00.1
- 20°F (0.05 - 11.1°C) are possible.
For normal pulldowns and quick response, a RATE
CONTROL TEMP of 0.1°F (0.05°C) is appropriate un-
less excessive overshoot is noted.
For demand limiting, energy efficiency and minimum
cycling, RATE CONTROL TEMPS of 10° - 20°F (5.6 -
11.1°C) are advisable with temperatures around 20°F
(11.1°C) most appropriate. This will cause the control to
react to water temperature rate of change well before the
FIG. 14 – RETURN WATER TEMPERATURE CONTROL
65°
(18.3°)
55°
(12.8°)
45°
(7.2°)
UPPER LIMIT OF RATE
CONTROL RANGE
UPPER LIMIT OF
CONTROL
RANGE (CR)
SETPOINT
ABOVE THE RATE CONTROL
TEMP RANGE
D
RATE CONTROL TEMP RANGE
(RATE CONTROL TEMP = 10°F [5.5°C])
E
D
CONTROL RANGE
(CR = 45 - 55°F [7.2 - 12.8°C])
E
BELOW THE CONTROL RANGE