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CVHE-SVX005C-EN
Figure 59. Sequence of operation: ice building: auto to ice to ice building complete to auto
Evap Entering Water
Temp Falls Below the
Ice Termination
Setpoint
Running
(Ice Building)
Open IGV at MaxRate/Max
AFD Frequency
Close IGV /Min AFD
Frequency
Enforce All Limits and Running Mode Diagnostics
Command Ice Building via:
1. Front Panel OD (On)
2. Tracer (On)
3. External Input (Close/Short)
Energize
Ice Building Relay
Ignore Softloading and Set
DLS = 100%
De-Energize Ice
Building Relay
De-Energize Head Relief
Request Relay
Close IGV
(0-50 Seconds)
Shutting Down
(Ice Building
Complete)
Energize Head Relief
Request Relay
Head Relief Request Relay Delay
(1 to 60 Mins)
Preparing Shutdown
(Ice Building Complete)
De-Energize Oil Pump
De-Energize
Compressor
Post Lube
(3 Minutes)
Ignore Evap Pump Off
Delay Time For Ice
Building
De-Energize Evaporator
Water Pump Relay
De-Energize Condenser
Water Pump Relay
Confirm No Compressor Currents
Within 8 Seconds
Auto
(Waiting For A
Need To Cool)
Run Inhibit
(Ice Building
Complete)
Remove all Ice Building Commands via:
1. Front Panel OD (Auto)
2. Tracer (Auto)
3. External Input (Open)
Evap Entering Water Temp Rises
above the Ice Termination Setpoint
Auto
(Waiting For A
Need To Cool)
Auto
(Waiting To
Start)
Auto
(Starting
Compressor)
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 exchanger.
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 operator 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. The
following components must be factory- or field-installed to
equip the unit for free cooling operation:
• a refrigerant gas line, and electrically-actuated shutoff
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 economizer),
and
• additional refrigerant.
When the chiller is changed over to the free cooling mode,
the compressor will shutdown if running and 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 pressure 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, cooling tower water causes
the refrigerant to condense on the condenser tubes, 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 changeover 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 (refer to the figure
in “Start-up Sequence of Operation—Wye-delta,” p. 76
[power up to starting], 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
Start-Up and Shutdown
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