York YCAZ33BA3, Руководство пользователя, Страница: 46 / 88

YORK INTERNATIONAL
46
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 during which loading will occur at 1 min. intervals.
This allows the chiller to gain control of the water tem-
perature as quickly as possible while still avoiding over-
shoot and limiting pulidown demand as temperature
drops and rate control is implemented.
Since LWT Control does not have the water loop for
buffering after a load/unload response and utilizes a
narrow control (loading/unloading) range, compressor/
loader cycling can be a problem. This makes the se-
lection of RATE CONTROL TEMP and RATE SEN-
SITIVITY values very critical.
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
0.1-20°F are possible.
For normal pulldowns, and quick response, a RATE
CONTROL TEMPS of 0-1°F is appropriate unless
overshoot is noted.
For demand limiting, energy efficiency, elimination of
overshoot, and minimum cycling, RATE CONTROL
TEMPS of 10-20°F are advisable. This will cause the
controls to react to water temperature rate of change
well before the water temperature drops into the CON-
TROL 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”. Exam-
ple: 0.5-9°F.
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 temperatures are in the RATE CONTROL
Additionally, 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. 14 as you read the following text. A typical
low limit water temperature of 44°F is used with a 44°-
6°F CONTROL RANGE (CR). A RATE CONTROL
TEMP of 10°F, which is typical (10° above upper limit
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 the above example a RATE CON-
TROL TEMP of 10°F is used. In the Rate Control Range,
the micro will prevent loading or may cause unloading
if the temperature drop exceeds 2X the Rate Sensitiv-
ity regardless of whether the 150 sec. Ioading timer
and the deviation from setpoint is calling for loading.
At temperatures below the CONTROL RANGE, unload-
ing will occur to bring temperatures back to within the
CONTROL RANGE. The unloading timer will cause un-
loading at 20 sec. intervals until temperatures fall back
into the CONTROL RANGE.
In the lower half of the Control Range between the Low
Limit Water Setpoint (LWT) and the “Target” Tempera-
ture (Desired Leaving Water Temperature), Rate Con-
trol software will cause unloading if temperature drops
faster than 1X the Rate Sensitivity. Otherwise, no other
loading or unloading will result in this temperature range.
In the upper half of the Control Range between the TAR-
GET and the High Limit of the Control Range and in the
Rate Control Range, loading will take place in 150 sec.
intervals until temperature drops below the TARGET tem-
perature. The Rate Control software may prevent load-
ing or possibly initiate unloading if temperature drops
faster than 2X the programmed Rate Sensitivity.
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56°
46°
45°
44°
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)
TARGET
(CR = 44 - 46°F)
LOW LIMIT
OF CONTROL
BELOW THE RANGE (LWT)
CONTROL RANGE
FIG. 14 – LEAVING WATER TEMPERATURE CONTROL
R A T E C O N T R O L T E M P
= 1 0 . 0 F