Free Cooling Cycle
Based on the principle that refrigerant migrates to the
coldest area in the system, the free cooling option adapts
the basic chiller to function as a simple heat exchang-
er. However, it does not provide control of the leaving
chilled water temperature.
If condenser water is available at a temperature lower
than the required leaving chilled water temperature, the
operator interface must remain in AUTO and the oper-
ator starts the free cooling cycle by enabling the Free
cooling mode in the Tracer AdaptiView Feature Settings
group of the
operator interface, or by means of a BAS request. Sever-
al components must be factory-installed or field-installed
to equip the unit for free cooling operation:
• a refrigerant gas line, and electrically-actuated shut-
off valve, between the evaporator and condenser;
• a valved liquid return line, and electrically-actuated
shutoff valve, between the condenser sump and the
evaporator;
• a liquid refrigerant storage vessel (larger economiz-
er); and,
• additional refrigerant.
When the chiller is changed over to the free cooling
mode, the compressor will shut down if running, the
shutoff valves in the liquid and gas lines open; unit
control logic prevents the compressor from energizing
during free cooling. Liquid refrigerant then drains (by
gravity) from the storage tank into the evaporator and
floods the tube bundle. Since the temperature and pres-
sure of the refrigerant in the evaporator are higher than
in the condenser (i.e., because of the difference in water
temperature), the refrigerant in the evaporator vaporizes
and travels to the condenser, water causes the refriger-
ant to condense, and flow (again, by gravity) back to the
evaporator.
This compulsory refrigerant cycle is sustained as long as
a temperature differential exists between condenser and
evaporator water. The actual cooling capacity provided
by the free cooling cycle is determined by the difference
between these temperatures which, in turn, determines
the rate of refrigerant flow between the evaporator and
condenser shells.
If the system load exceeds the available free cooling
capacity, the operator must manually initiate change-
over to the mechanical cooling mode by disabling the
free cooling mode of operation. The gas and liquid line
valves then close and compressor operation begins (see
beginning at Auto mode). Refrigerant gas is drawn out
of the evaporator by the compressor, where it is then
compressed and discharged to the condenser. Most of
the condensed refrigerant initially follows the path of
least resistance by flowing into the storage tank. This
tank is vented to the economizer sump 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. Free Cooling must first be installed and commis-
sioned.
2. Enable the Free Cooling mode in the Tracer AdaptiV-
iew 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.
Free Cooling cannot be entered if the chiller is in “STOP”.
If the chiller is in AUTO and not running, the condens-
er 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 pow-
ered cooling, the chiller will initiate a friendly shut down
first (Run: Unload, Post Lube, and drive vanes closed).
After the vanes have been overdriven closed and con-
denser 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. Once 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.
Note: 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.
Note: 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 guide vanes and the HGBP valve to
TCVHE-SVX04D-EN 59
Start-up and Shut Down
RELEASED 10/Mar/2020 06:59:20 GMT
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