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SECTION 17 - REFRIGERANT LEVEL CONTROL
the programmable Valve Preset Time setpoint (0
to 100 seconds; default 50). After pre-positioning,
the valve is held in this position until the first 3
minutes of Chiller Run Time has elapsed (Set-
ting the Valve Preset Time to 0 seconds disables
this pre-positioning feature). During this 3 minute
period, the Refrigerant Level Override displays
VALVE PRESET and the Override Time Remain-
ing displays the time remaining in the 3-minute
countdown timer. After the chiller has been run-
ning 3 minutes, if the level is greater than or
equal to the Refrigerant Level setpoint, it begins
controlling to the setpoint (with software version
C.OPT.01.21.307 (and later), after entering Sys-
tem run, if the refrigerant level is greater than the
programmed Level setpoint for 2 seconds, the pre-
set/hold timer is canceled and normal level con-
trol is started immediately, regardless of whether
or not the Preset position has been reached or the
3 minute timer has elapsed).
However, if it is less than the Refrigerant Level
setpoint, a linearly increasing ramp limit, called the
Refrigerant Level Target, is applied to the Refrigerant
Level setpoint. This ramp limit allows the level to go
from the present level to the Refrigerant Level setpoint
over a period of time programmed as the Ramp-Up
Time setpoint (3 to 15 minutes; default 8). During this
ramp-up period, the Refrigerant Level Target is used to
control the refrigerant level in the condenser and the
Refrigerant Level setpoint message on the CONDENS-
ER Screen is replaced by REFRIGERANT LEVEL
TARGET = XX%. While the ramp is in effect, RAMP
UP TIME REMAINING = XX MIN is displayed. Af-
ter the ramp period has elapsed, the refrigerant level
is controlled by the Refrigerant Level setpoint for the
remainder of chiller run. If the Valve Preset Time is set
to 0 seconds and the Ramp-Up Time setpoint is set to
15 minutes, the control will operate the same as previ-
ous Software versions, as
The Program applies an open or close signal, as re-
quired, from the microboard to the actuator to maintain
the level to the Level setpoint. The duration of the sig-
nal determines the magnitude of change to the Orifice
position. The duration of the signal and whether it is an
open or close signal depends upon the Proportion Error
and the Rate of Change of the actual level compared to
the Level setpoint in a recurring period of time called
a Level Control Period. At the end of each Level Con-
trol Period, the Proportion error and Rate of Change
166
described above.
JCI COMPANY CONFIDENTIAL
are compared to control thresholds Proportion Limit
Close, Proportion Limit Open and Rate Limit Close
and Rate Limit Open. The result of this comparison de-
termines the signal that will be applied to the actuator
at the end of the Level Control Period as explained be-
low. The setpoint values used by the program is deter-
mined by the Software vintage. In earlier versions, the
values are programmable setpoints as shown below. In
later versions, they are fixed and programmable values
applied in two different Zones, as determined by the
error relationship of the actual refrigerant level and the
Level setpoint as shown below.
Software version C.MLM.01.11.xxx (and earlier)
or C.OPT.01.11.xxx (and earlier)
• Level Control Period - 3.5 to 30.0 seconds (de-
fault 3.5)
• Proportion Limit Open - 10% to 50% (default 15)
• Proportion Limit Close -10% to 50% (default 45)
• Rate Limit Open - 5% to 50% (default 10)
• Rate Limit Close - 5% to 50% (default 10)
• Proportion Error Deadband - +3%
• Rate Error Deadband - +1%
Software version C.MLM.01.14.xxx (and later) or
C.OPT.01.14.306(and later)
In this version, some control thresholds are fixed while
others are programmable. This provides more stable
control in certain operating conditions. The control
thresholds are applied in two different zones, as de-
termined by the error relationship between the actual
refrigerant level and the Level setpoint as shown be-
low. Zone 1 parameters are used when the error is less
than 9%. Zone 2 parameters are used when the error
is greater than 9%. When transitioning from Zone 2 to
Zone 1, the error must be less than 9% for 60 seconds
before the Zone 1 parameters are used. If the error is
greater than 9%, the Zone 2 parameters are immedi-
ately implemented.
On the REFRIGERANT LEVEL CONTROL Screen,
the Zone Control State status box displays which zone
of control is being used:
• ZONE 1
• ZONE 2
• ZONE CONTROL OFF (if chiller shutdown)
FORM 160.54-M1
ISSUE DATE: 10/25/2019
JOHNSON CONTROLS
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