134
YORK INTERNATIONAL
FORM 150.52-NM2 (1001)
00407VIP
is simply called the “Range” and is best described as
the maximum acce 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 +/- 1.0°C (2°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 total tem-
perature range is called the Control Range and can be
viewed pictorially as follows:
6. SETPOINTS KEYS AND 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, by varying the number of cylinders loaded on each
compressor, and by controlling the hot gas valve. The
microprocessor controls chilled liquid temperature
through a combination of Fuzzy Logic control and inter-
nal timers. Fuzzy Logic enables the micro to analyze
the deviation from setpoint and the rate of change and
determine whether compressors need to be started or
stopped, increase/decrease compressor load stages, or
whether to turn the hot gas bypass on or off to control
chilled liquid temperature to the desired setpoint. The
micro also attempts to minimize cycling. This method of
control is suitable for both water and brine cooling. Con-
trol setpoints can be programmed into the chiller to es-
tablish the desired range of leaving chilled liquid operat-
ing temperatures. A description of the operation and pro-
gramming 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
7.0°C
(44.0°F)
SETPOINT
Temp.
(User accept-
able leaving
chilled liquid
operating
range)
CONTROL
RANGE
8.0°C
(46.0°F)
6.0°C
(42.0°F)
SETPOINTS
KEYS
Micro Panel