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YORK INTERNATIONAL
viation from setpoint. Rate Control will function to pre-
vent loading if the water temperature change (leaving or
return) exceeds the RATE SENSITIVITY, 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 every 60 seconds per stage.
This allows the chiller to gain control of the water tem-
perature as quickly as possible.
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
allowable pulldowns are required or whether pulldown
demand 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 ex-
cessive overshoot 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 is also a must 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.
Loading may be inhibited or unloading may occur if the
micro senses that the Rate Sensitivity is exceeded in
the Control Range or Rate Control Range to prevent over-
shoot. This action will override incremental loading.
Further details regarding 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
beyond normal responses dictated by the difference be-
tween actual return water temperature and setpoint.
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. 16 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, or unload if
the rate of change of water temperature reduction ex-
ceeds the programmed RATE SENSITIVITY. In Fig. 16 a
RATE CONTROL TEMP of 10°F is used.
In the CONTROL RANGE and RATE CONTROL RANGE
loading/unloading will normally occur according to de-
FIG. 16
RETURN WATER TEMPERATURE CONTROL
65°
55°
45°
UPPER LIMIT OF
RATE CONTROL
RANGE
UPPER LIMIT OF
CONTROL
RANGE (CR)
SETPOINT
ABOVE THE RATE CONTROL
TEMP RANGE
h
RATE CONTROL TEMP RANGE
(RATE CONTROL TEMP = 10°F)
i
h
CONTROL RANGE
(CR = 45 - 55°F)
i
BELOW THE CONTROL RANGE
R A T E
C O N T R O L
T E M P
=
1 0 . 0
F
Summary of Contents for YCWJ45EE0
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