York YST Operation Manual page 62

SECTION 2 - OPTIVIEW CONTROL CENTER INTRODUCTION
vane ramp signal is at 97% or the leaving chilled liq-
uid temperature decreases to within 2 °F of the present
setpoint. It is also Inactive if any override controller is
active, in which case its' output is equal to the override
block output. It becomes Active after the override con-
troller is no longer controlling and the TDSP10-Temp
Control Override Transfer Delay shown on the Capac-
ity Control Setpoints Screen 1 has elapsed.
Temperature Control - Setpoint
Displays the present Leaving Chilled Liquid Tempera-
ture Setpoint used to control the chiller. This may be
the Local Setpoint entered on the Setpoints Screen or
the Remote Setpoint if being controlled by a remote
signal.
Temperature Control - leaving Chilled liquid
Temperature
Displays the present temperature of the liquid as it
leaves the evaporator.
prv ramp
Displays the present signal leaving the PRV Ramp log-
ic. It is based on the RRSP8-PRV Ramp Rate shown on
the Capacity Control Setpoints Screen 1. On startup,
when the ramp up to rated speed commences, this out-
put is set at the PRVM- PRV Minimum Open Position
shown on Capacity Control setpoints Screen 2. It is
used to provide a controlled loading rate after the chill-
er has been ramped up to the minimum rated speed.
prv position
Displays the present position of the compressor pre-ro-
tation vanes as sensed by the potentiometer on the vane
operating shaft. This display will lag behind the Pre-
Rotation Vanes control signal display but will eventu-
ally be within 1% of the Pre-Rotation Vanes control
signal display after the vane actuator has finished mov-
ing.
hgv ramp
Displays the present signal leaving the HGV Ramp
logic. It is based on the RRSP9-Hot Gas Valve Ramp
Rate shown on the Capacity Control Setpoints Screen
1. It is used to provide a controlled loading rate after
the chiller has been ramped up to the minimum rated
speed.
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Capacity Control box
This box displays parameters pertinent to the Capac-
ity Control Ratchet Mode Selector. This selector deter-
mines which device should be used for capacity control
and ensures that the chiller is always operating as ef-
ficiently as possible. The data field below the Capacity
Control text displays Hot Gas, PRV, or Speed, depend-
ing on which device is presently being controlled.
Capacity Control – Spd
Displays the present Capacity Ratchet Mode Selec-
tor output signal for controlling the speed. The out-
put represents the % equivalent of the speed based on
0-4500 RPM being equal to 0-100%. When in the Hot
Gas mode, this value will be equal to the calculated
anti-surge minimum speed output. On startup, after the
chiller is running at or above the minimum rated speed,
the turbine stabilization delay has elapsed, and the Hot
Gas Bypass Valve is closing, as the system head in-
creases causing the calculated anti-surge minimum
speed output to increase, this output will increase to
maintain system stability. When the mode changes to
Speed after the PRV output is at 100%, this output will
increase as required to maintain the leaving chilled liq-
uid temperature at setpoint.
Capacity Control – prv
Displays the present Capacity Ratchet Mode Selec-
tor output signal for controlling the compressor pre-
rotation vanes. When in the Hot Gas mode, this value
will be equal to the calculated anti-surge minimum
PRV output. On startup, when the ramp up to rated
speed has commenced, the PRV Ramp output and the
Pre-Rotation Vanes signal are set to the PRVM- PRV
Minimum Open Position shown on Capacity Control
Setpoints Screen 2. When the mode changes to PRV af-
ter the HGV output is at 0%, the PRV Ramp output be-
gins increasing from the PRVM% to open the vanes. As
the system head increases, if the calculated anti-surge
minimum PRV output increases above the ramp output
signal, the HSR will select the high anti-surge signal to
maintain system stability. If the Leaving Chilled Liq-
uid Temperature Controller becomes Active and begins
to control this output, the LSR will select the lower of
this signal and the PRV Ramp output in order to main-
tain the leaving chilled liquid temperature at setpoint.
FORM 160.67-O1
ISSUE DATE: 4/1/2015
JOHNSON CONTROLS