FORM 150.60-NM4
YORK INTERNATIONAL
47
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 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°
-46°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 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 the above example a RATE CONTROL TEMP
of 10°F is used. In the Rate Control Range, the micro
will prevent loading or may cause unloading if the tem-
perature drop exceeds 2X the Rate Sensitivity regardless
of whether the 150 sec. loading 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 Control
software will cause unloading if temperature drops faster
than 1 X the Rate Sensitivity. Otherwise, no other load-
ing 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 loading
UPPER LIMIT OF CR
PLUS RATE
CONTROL TEMP
UPPER LIMIT OF
CONTROL RANGE (CR)
TARGET
LOW LIMIT
OF CONTROL
RANGE (LWT)
FIG. 14 – LEAVING WATER TEMPERATURE CONTROL
ABOVE THE RATE CONTROL
TEMP RANGE
!
RATE CONTROL TEMP RANGE
(RATE CONTROL TEMP = 10°F)
"
!
CONTROL RANGE
(CR = 44 - 46°F)
"
BELOW THE
CONTROL RANGE
56°
46°
45°
44°
or possibly initiate unloading if temperature drops faster
than 2X the programmed Rate Sensitivity.
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 pulldown demand as temperature drops
and rate control is implemented.
Since LWT Control does not have the water loop for buff-
ering after a load/unload response and utilizes a narrow
control (loading/unloading) range, compressor/loader
cycling can be a problem. This makes the selection of
RATE CONTROL TEMP and RATE SENSITIVITY values
very critical.
Before programming the RATE CONTROL TEMP, the user
should first determine if typically the fastest allowable
pulldowns are required or whether pulldown demand limiting
is desired. Programmable values from 0.1-20°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, 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°-9.9°F
The next item which will require programming is the RATE
SENSITIVITY.
R A T E
C O N T R O L
T E M P
=
1 0 . 0 F
