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Table 27. Operating Modes
Chiller Modes
Start Inhibited Waiting for Oil
Condenser Water Pump Pre-Run
Timemin:sec
Restart Inhibit min:sec
Waiting For EXV Preposition
Minimum Condenser Watermin:sec
Condenser Water Regulating Control
min:sec
Running
High Discharge Temp Limit
Base Loaded
Capacity Control Softloading
Current Control Softloading
EXV Controlling Differential Pressure
Chilled Water Control
Running – Limited
Condenser Pressure Limit
Low Evaporator Refrigerant Temperature
Inhibit
Capacity Limited by Low Liquid Level
Current Limit
Phase Unbalance Limit
Low Discharge Superheat Limit
Oil Loss Avoidance
High Motor Winding Temp Limit
Max CFM Limit
Low Water Temp Difference Limit
Note: Other normal running modes (see above) may also appear under this top level mode.
Shutting Down
Local Stop
immediate Stop
RTHD-SVX04K-EN
Description
The chiller will wait up to 2 minutes in this mode for oil level to appear in the oil tank.
The chiller will wait up to 30 minutes (user adjustable) in this mode for to allow the condens-
er water loop to equalize in temperature
The compressor is currently unable to start due to its restart inhibit timer. A given com-
pressor is not allowed to start until 5 minutes (adj) has expired since its last start, once a
number of "free starts" have been used up.
The Chiller will wait for the time it takes the EXV to get to its commanded pre-position prior
to starting the compressor. This is typically a relatively short delay and no countdown timer
is necessary (less than 15 seconds)
Only possible when Condenser Head Pressure Control option is enabled, this wait may be
necessary due to the Head Pressure control device's stroke time.
Only possible when Condenser Head Pressure Control option is enabled, this wait may be
necessary due to the Head Pressure control device's stroke time
The chiller, circuit, and compressor are currently running. Further information is
provided by the sub-mode:
The compressor is running and is being forced loaded to its step load point, without regard
to the leaving water temperature control, to prevent tripping on high compressor discharge
temperature.
Chiller is running in "Base Load" operation where the capacity of the chiller is controlled to
maintain a given current per an adjustable set point. The chiller is forced to run without re-
gard to the chilled water temperatures and the differential to start and stop
The chiller is running, but loading is influenced by a gradual 'pulldown" filter on the chilled
water temperature setpoint The settling time of this filter is user adjustable as part of the
softload control feature.
The chiller is running, but loading is influenced by a gradual filter on the current limit set-
point The starting current and the settling time of this filter is user adjustable as part of the
softload control feature.
Liquid level control of the Electronic Expansion Valve has temporarily been suspended. The
EXV is being modulated to control for a minimum differential pressure. This control implies
low liquid levels and higher approach temperatures, but is necessary to provide minimum oil
flow for the compressor until the condenser water loop can warm up to approx 50F.
Unit is running in the Cooling Mode of operation and is attempting to control to the active
Chilled Water Setpoint. (Note this mode was not necessary prior to the introduction of Hot
Water Control)
The chiller, circuit, and compressor are currently running, but the operation of the
chiller/compressor is being actively limited by the controls. Further information is
provided by the sub-mode.* See the section below regarding criteria for annuncia-
tion of limit modes
The circuit is experiencing condenser pressures at or near the condenser limit setting. Com-
pressors on the circuit will be unloaded to prevent exceeding the limits.*
The circuit is experiencing saturated evaporator temperatures at or near the Low Refrigerant
Temperature Cutout setting. Compressors on the circuit will be unloaded to prevent tripping.
*
The circuit is experiencing low refrigerant liquid levels and the EXV is at or near full open.
The compressors on the circuit will be unloaded to prevent tripping.*
The compressor is running and its capacity is being limited by high currents. The current
limit setting is 100% RLA (to avoid overcurrent trips) or lower as set by the compressor's
"share" of the active current limit (demand limit) setting for the entire chiller.*
The compressor is running and its capacity is being limited by excessive phase current unbal-
ance.*
This is limit control that acts to prevent chiller shutdown when the discharge superheat ap-
proaches the limit setpoint by reducing the liquid level and unloading the slide valve.
This is limit control that acts to prevent chiller shutdown when the estimated refrigerant flow
approaches the calculated minimum flow by increasing the slide valve capacity and/or VFD
frequency
This is limit control that acts to prevent chiller shutdown when the measured motor temp
approaches limit setpoint by increasing compressor capacity.
This is limit control that acts to prevent chiller shutdown when the estimated evaporator
refrigerant flow approaches the calculated maximum flow by limiting maximum compressor
capacity.
This is limit control that acts to prevent too much refrigerant flow bypass from condenser to
compressor that will cause very low efficiency.
The chiller is still running but shutdown is imminent. The chiller is going through a
compressor run-unload. sequence. Shutdown is necessary due to one (or more) of
the following sub-modes:
Chiller is in the process of being stopped by TD7 Stop button command
Chiller is in the process of being stopped by TD7 Panic Stop command
Operator Interface Controls
93
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