York YST Operation Manual page 58

SECTION 2 - OPTIVIEW CONTROL CENTER INTRODUCTION
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 start-
up, when the ramp up to rated speed has commenced,
this output 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 chiller has been ramped up to the minimum rated
speed.
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.
hot gas ratio Calculation
Displays the present signal leaving the Hot Gas Ratio
Calculation. The Hot Gas Ratio calculation controls
the hot gas bypass valve at a scaled ratio to the percent-
age of available capacity control signal below the Min-
imum Vane Position Calculation output, thus providing
a 0-100% control signal for the hot gas bypass valve.
The capacity control signal from the Leaving Chilled
Liquid Controller/Override Limit decreases to close
the vanes to the calculated anti-surge minimum value.
Therefore, if the vane signal is stopped at 20% and the
capacity control signal continues to decrease, the out-
put of this calculation will increase from 0-100% as the
control signal decreases from 20-0% to fully open the
Hot Gas Bypass Valve if required.
hot gas ratio Setpoint
Displays the HGVRAT-Hot Gas Valve Ratio Bypass
setpoint shown on Capacity Control Setpoints Screen
1. This output is used to establish a minimum vane
position above the calculated anti-surge value to pro-
vide greater stability at very low system pressure dif-
ferentials when the minimum vane position calcula-
tion would normally be 0%. Therefore, the vanes are
prevented from closing below this value, and the Hot
Gas Ratio Calculation uses this minimum signal as the
starting point for controlling the Hot Gas Bypass Valve.
58
Hot gas Temp Calculation
Displays the present output signal from the Hot Gas
Valve Temperature Controller. In some cases, it may
be desirable to allow the vanes to go completely closed
which would leave no signal for the Hot Gas Ratio
calculation to control the hot gas valve. The Hot Gas
Temp Calculation is a separate PID controller which
controls at the Temp Setpoint which is equal to the
present Leaving Chilled Liquid Temperature Setpoint
minus the TSP3-Hot Gas Valve Temp Controller SP
Diff shown on Capacity Control Setpoints Screen 1.
The output displayed will increase to open the Hot
Gas Bypass Valve and unload the chiller if the Leav-
ing Chilled Liquid Temperature is below the Temp
Setpoint. The response time of the controller is deter-
mined by the HGV control mode tuning entered on the
PID Setup Screen 1 for the Temperature Control.
Speed Setpoint
Displays the present setpoint of the Speed Control PID
controller. This setpoint is automatically controlled by
the chiller sequencing logic during startup and shut-
down. The Governor Valve output displayed will in-
crease to open the pneumatically actuated governor
valve on the turbine if the Turbine Speed is below this
setpoint. The Slow Roll, Min Rated, and Rated tuning
values entered on the PID Setup Screen 2 determine
the response time of the Speed Control PID controller.
Turbine Speed
Displays the highest of the two speed input signals
sensed by two magnetic pickups that monitor a toothed
gear installed on the turbine shaft.
governor valve
Displays the present control signal being sent to the
analog output used to control the I/P transducer on the
pneumatically actuated governor valve. The data field
below the output display shows the Auto/Manual status
of the Speed Setpoint as presently selected on the Auto/
Manual Screen.
hot gas bypass
Displays the present control signal being sent to the
analog output used to control Hot Gas Bypass Valve
actuator. The data field below the output display shows
the Auto/Manual status of the Hot Gas Bypass as
presently selected on the Auto/Manual Screen.
FORM 160.67-O1
ISSUE DATE: 4/1/2015
JOHNSON CONTROLS