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through a small bleed line; when the storage tank is full,
liquid refrigerant must flow through the bleed line
restriction. Because the pressure drop through the bleed
line is greater than that of the orifice flow control device, the
liquid refrigerant flows normally from the condenser
through the orifice system and into the economizer.
Free Cooling (FRCL)
To enable Free Cooling mode:
1. Install and commission Free Cooling.
2. Enable the Free Cooling mode in the Tracer®
AdaptiView™ Settings menu.
3. Press AUTO, and if used, close the external binary
input switch (connected to 1A20 J2-1 to 2) while the
chiller is in AUTO.
Note: Free Cooling cannot be entered if the chiller is in
STOP.
If the chiller is in AUTO and not running, the condenser
water pump will start. After condenser water flow is proven,
Relay Module 1A11 will energize operating the Free
Cooling Valves 4B12 and 4B13. The Free Cooling Valves
End Switches must open within 3 minutes, or an MMR
diagnostic will be generated. Once the Free Cooling Valves
End Switches open, the unit is in the Free Cooling mode. If
the chiller is in AUTO and running powered cooling, the
chiller will initiate a friendly shutdown first (Run: Unload,
Post Lube, and drive vanes closed). After the vanes have
been overdriven closed and condenser water flow proven,
the Free Cooling relays will be energized. To disable Free
Cooling and return to Powered Cooling, either disable the
Free Cooling Mode in the Tracer AdaptiView Settings menu
if used to enable Free Cooling, or OPEN the external
binary input switch to the 1A20 Module if it was used to
enable Free Cooling. Once Free Cooling is disabled, the
Free Cooling relays Relay Module 1A11 will de-energize
allowing the Free Cooling valves to close. The Free
Cooling valves end switches must close within 3 minutes or
an MMR diagnostic is generated. After the end switches
close, the chiller will return to AUTO and powered cooling
will resume if there is a call for cooling based on the
differential to start.
Notes:
•
The manual control of the inlet guide vanes is
disabled while in the Free Cooling mode and
the compressor is prevented from starting by
the control logic.
•
The relay at 1A11-J2-4 to 6 is a FC auxiliary
relay and can be used as required.
Hot Gas Bypass (HGBP)
The hot gas bypass (HGBP) control option is designed to
minimize machine cycling by allowing the chiller to operate
stably under minimum load conditions. In these situations,
the inlet guide vanes are locked at a preset minimum
position, and unit capacity is governed by the HGBP valve
actuator. Control circuitry is designed to allow both the inlet
CVHE-SVX005C-EN
guide vanes and the HGBP valve to close for unit shut-
down. After a chiller starts and is running, the inlet guide
vanes will pass through the HGBP Cut-In-Vane position as
the chiller starts to load. As the chiller catches the load and
starts to unload, the inlet guide vanes will close to the Hot
Gas Bypass Cprsr Ctrl Command position. At this point, the
movement of the inlet guide vanes is stopped and further
loading/unloading of the chiller is controlled by the opening/
closing of the HGBP Valve (4M5). When the control
algorithm determines the chiller to be shut down, the inlet
guide vanes will be driven fully closed and the HGBP valve
will be driven closed. After the inlet guide vanes are fully
closed, the chiller will shut down in the Friendly mode.
Chillers with HGBP have a discharge temperature sensor
(4R16) monitoring the discharge gas temperature from the
compressor. If this temperature exceeds the High Cprsr
Rfgt Discharge Temp Cutout 200°F (93.3°C) default, the
chiller will shut off on a MAR diagnostic. The chiller will
reset automatically when this temperature drops 50°F
(10.0°C) below the trip-point. HGBP is enabled in the
Features Menu Settings group of the Tracer®
AdaptiView™ menus by enabling the option. The setting of
the HGBP Cut-In Vane Position is set-up at unit
commissioning via the service tool.
Hot Water Control
Occasionally, CenTraVac™ chillers are selected to provide
heating as a primary mission. With hot water temperature
control, the chiller can be used as a heating source or
cooling source. This feature provides greater application
flexibility. In this case, the operator selects a hot water
temperature and the chiller capacity is modulated to
maintain the hot water setpoint. Heating is the primary
mission and cooling is a waste product or is a secondary
mission. This type of operation requires an endless source
of evaporator load (heat), such as well or lake water. The
chiller has only one condenser.
Note: Hot Water Temperature Control mode does NOT
convert the chiller to a heat pump. Heat pump refers
to the capability to change from a cooling-driven
application to a heating-driven application by
changing the refrigerant path on the chiller. This is
impractical for centrifugal chillers as it would be
much easier to switch over the water side.
This is NOT heat recovery. Although this feature could be
used to recover heat in some form, a heat recovery unit has
a second heat exchanger on the condenser side.
The Tracer® Symbio™ 800 provides the Hot Water
Temperature Control mode as standard. The leaving
condenser water temperature is controlled to a hot water
setpoint between 80°F and 140°F (26.7°C and 60.0°C).
The leaving evaporator water temperature is left to drift to
satisfy the heating load of the condenser. In this
application, the evaporator is normally piped into a lake,
well, or other source of constant temperature water for the
purpose of extracting heat. In Hot Water Temperature
Control mode, all the limit modes and diagnostics operate
as in normal cooling with one exception: the leaving
Start-Up and Shutdown
83
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