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YORK INTERNATIONAL
Overriding of the timer will depend upon the Rate Control
software which is user programmable. The Rate Control
software will totally inhibit loading in the CR (CONTROL
RANGE) and the Rate Control Range if temperature drop
exceeds the rate sensitivity even though temperature may
appear to require loading.
Further details of loading/unloading and Rate Control will
follow.
PROGRAMMING
RETURN WATER RATE CONTROL
Programmable RATE CONTROL is designed to limit com-
pressor/loader cycling thus saving energy and reducing
wear on mechanical components. It also reduces the
possibility of “overshoot”. RATE CONTROL will allow the
micro to react to fast changes in water temperature be-
yond normal responses dictated by the difference be-
tween actual return water temperature versus setpoint
and the 30 sec. loading/unloading timer per stage.
RATE CONTROL requires programming the temperature
range (RATE CONTROL TEMP) above the CONTROL
RANGE (CR) where rate control is desired. Additionally,
the actual rate of change (RATE SENSITIVITY) of water
temperature which the micro uses as a control refer-
ence must also be programmed.
Refer to Fig. 13 as you read the following text. A typical
leaving water temperature setpoint of 45°F is used with
a 45° - 55°F CONTROL RANGE. A RATE CONTROL
TEMP OF 65°F, which is typical (10° above the high end
of the Control Range), is shown.
The RATE CONTROL TEMP establishes a temperature
range (0.1° - 20°F) above the “Upper Limit of CONTROL
RANGE” where the micro will limit loading if the rate of
change of water temperature exceeds the RATE SEN-
SITIVITY. In Fig. 13 a RATE CONTROL TEMP of 10°F is
used.
In the CONTROL RANGE loading/unloading will normally
occur according to deviation from setpoint. “Rate Con-
trol” will function to prevent loading if the water tempera-
ture change (leaving or return) exceeds the RATE SEN-
SITIVITY, even though deviation 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 as fast as it can (30 sec-
onds per stage) unless the chiller has not run for 3 min-
utes. This allows the chiller to gain control of the water
temperature as quickly as possible while still avoiding
overshoot 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 are possible.
For normal pulldowns, and quick response, a RATE
CONTROL TEMP of 0.1°F is appropriate unless over-
shoot is noted.
For demand limiting, energy efficiency, and minimum
cycling, RATE CONTROL TEMPS of 10° - 20°F are ad-
visable with temperatures around 20°F most appropriate.
This will cause the control to react to water temperature
rate of change well before the 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.
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.
NOTE: When programming values between 0.1° - 9.9°F,
it is required to first key in a “0” or “00”. Ex-
ample: 05.9°F.
FIG. 13 – RETURN WATER TEMPERATURE CONTROL
65°
55°
45°
UPPER LIMIT OF CR
PLUS RATE
CONTROL TEMP
UPPER LIMIT OF
CONTROL
RANGE (CR)
SETPOINT
ABOVE THE RATE CONTROL
TEMP RANGE
!
RATE CONTROL TEMP RANGE
(RATE CONTROL TEMP = 10°F)
"
!
CONTROL RANGE
(CR = 45 - 55°F)
"
BELOW THE CONTROL RANGE
R A T E
C O N T R O L
T E M P
=
1 0 . 0
F
