York YCAZ33BA3, Руководство пользователя, Страница: 43 / 88

FORM 150.44-NM4
43
YORK INTERNATIONAL
Overriding of the timer will depend upon the Rate Con-
trol 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
compressor/loader cycling thus saving energy and re-
ducing wear on mechanical components. It also reduces
the possibility of “overshoot”. RATE CONTROL will al-
low the micro to react to fast changes in water tempera-
ture beyond normal responses dictated by the difference
between actual return water temperature versus setpoint
and the 30 sec. Ioading/unloading timer per stage.
RATE CONTROL requires programming the tempera-
ture range (RATE CONTROL TEMP) above the CON-
TROL RANGE (CR) where rate control is desired. Ad-
ditionally, the actual rate of change (RATE SENSI-
TIVITY) of water temperature which the micro uses as
a control reference 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 tempera-
ture range (0.1° - 20°F) above the “Upper Limit of CON-
TROL RANGE” where the micro will limit loading if the
rate of change of water temperature exceeds the RATE
SENSITIVITY. In Fig. 13 a RATE CONTROL TEMP of
10°F is used.
In the CONTROL RANGE loading/unloading will nor-
mally occur according to deviation from setpoint. “Rate
Control” will function to prevent loading if the water tem-
perature change (leaving or return) exceeds the RATE
SENSITIVITY, even though deviation from setpoint re-
quires loading. This will reduce the chance of overshoot.
Above THE RATE CONTROL TEMP RANGE, the mi-
cro will attempt to load the chiller as fast as it can (30
seconds per stage) unless the chiller has not run for 3
minutes. This allows the chiller to gain control of the
water temperature as quickly as possible while still
avoiding overshoot and limiting pulidown 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
mechanical parts is reduced, and pulidown demand is
automatically 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 fastest allow-
able pulldowns are required or whether pulidown 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
overshoot is noted.
For demand limiting, energy efficiency, and minimum
cycling, RATE CONTROL TEMPS of 10° - 20°F are
advisable with temperatures around 20°F most appro-
priate. This will cause the control to react to water tem-
perature rate of change well before the water tem-
perature drops into the CONTROL RANGE. This may
be required for small water loops. However, if prob-
lems 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.
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65°
55°
45°
ABOVE THE RATE CONTROL
TEMP RANGE UPPER LIMIT OF
CR PLUS RATE
CONTROL TEMP
RATE CONTROL TEMP RANGE
(RATE CONTROL TEMP = 10°F)
UPPER LIMIT OF
CONTROL RANGE
(CR)
CONTROL RANGE (CR)
(CR = 45 - 55°F)
SETPOINT
BELOW THE
CONTROL RANGE
FIG. 13 – RETURN WATER TEMPERATURE CONTROL
R A T E C O N T R O L T E M P
= 1 0 . 0 F