92
CVHH-SVX001G-EN
Figure 57.
Sequence of operation: ice building: stopped to ice to ice building complete
Ice Making Command:
1. Front Panel
2. Tracer
3. External Input
Evap Entering
Water Temp Falls
Below the Ice
Termination
Setpoint
Auto
Run Inhibit
(Ice Building
Complete)
Starting
Compressor
Running
(Ice Building)
Preparing to
Shut Down
Shutting
Down
Run
Inhibit
Open IGV at Max Rate/
Max AFD Frequency
Close IGV
(0–50 sec)
Postlube
(3 min)
Heat Relief Request Relay
Delay (1–60 min)
Ignore Evap Pump
Off Delay Time
for Ice Building
Close IGV/Min AFD
Frequency
De-Energize Oil Pump
Open Oil Vent Line Valve
Hold position of Oil Vent Line Valve
De-Energize
Condenser
Water Pump Relay
De-Energize Evaporator
Water Pump Relay
De-Energize
Compressor
Confirm No Compressor Currents
Within 8 sec
Ignore Softloading and
Set CLS=100%
Energize Ice Building
Relay
Begin Oil Vent Line
Valve low limit venting
Enforce All Limits and Running Mode Diagnostics
De-Energize Ice
Building Relay
De-Energize Heat
Relief Request Relay
Energize Head Relief
Request Relay
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, and
•
a valved liquid return line, and electrically-actuated
shutoff valve, between the condenser sump and the
evaporator.
When the chiller is changed over to the free cooling
mode, the compressor will shut down if running and
the shutoff valves in the liquid and gas lines open; unit
control logic prevents the compressor from energizing
during free cooling. 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
Sequence of Operation—Wye-delta,” p. 87
[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.
Summary of Contents for CVHH CenTraVac
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