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Micro Panel Contents
6. SETPOINTS KEYS & CHILLED LIQUID CONTROL
6.1
GENERAL
The microprocessor monitors leaving chilled liquid tem-
perature and adjusts the chiller cooling capacity to main-
tain this temperature within a programmed range. The
capacity is controlled by switching compressors on or
off, and by varying a load/unload current to each com-
pressor slide valve to adjust the capacity of the com-
pressors. The microprocessor controls chilled liquid
temperature through a combination of Fuzzy Logic con-
trol and internal timers. Fuzzy Logic enables the micro
to analyze the deviation from setpoint and the rate of
change and determine the amount of loading and un-
loading necessary to control to the desired chilled liq-
uid setpoint temperature. The micro also attempts to
maximize efficiency by spreading the cooling load be-
tween compressors, minimize compressor cycling, and
optimally utilize evaporator tube surface (maximize
efficiency). This method of control is suitable for both
water and brine cooling. Control setpoints can be pro-
grammed into the chiller to establish the desired range
of leaving chilled liquid operating temperatures. A de-
scription of the operation and programming follows.
6.2
CHILLED LIQUID TEMPERATURE
CONTROL
The Setpoints keys are used to program the required
chilled water liquid temperature for the application. This
is accomplished by programming the "Setpoint" and
the acceptable deviation (+ or - Range) This deviation is
132
simply called the "Range" and is best described as the
maximum acceptable + and - deviation from Setpoint.
The minimum acceptable temperature is the Lower
Range and is calculated by subtracting the "-" Range
from the Setpoint. The Lower Range is the lowest ac-
ceptable leaving temperature. The highest acceptable
temperature is referred to as the Upper Range and is
calculated by adding the "+" Range to the Setpoint. The
Upper Range is the highest acceptable leaving tempera-
ture. For example, if the desired Setpoint temperature
is 7°C (44.0°F) and the allowable deviation (+ / - Range)
from this temperature is +/- 1°C (2.0°F), then the micro
will attempt to control leaving chilled liquid tempera-
tures to 6°C (42.0°F) to 8°C (46.0°F). This can be
viewed pictorially as follows:
8°C
(46.0°F)
SETPOINT
7°C
Temp.
(44.0°F)
6ºC
(42.0ºF)
To assure that the chilled liquid leaving temperature
stays within the Control Range, the micro will attempt
to control the leaving temperature to the actual Setpoint
temperature. This is accomplished by analyzing the tem-
SETPOINTS
KEYS
29023A
(User
acceptable
CONTROL
leaving
RANGE
chilled liquid
operating
range)
YORK INTERNATIONAL
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