Start-up and Shut-down
80 CVHH-SVX001A-EN
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-installed 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, 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 (see
Figure 42, p. 76, 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.
Hot Water Control
Occasionally CTV 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
u sed t o r ec o v e r h e at i n s o m e f o r m , a h e at r ec o v e r y u n i t h a s
a second heat exchanger on the condenser side.
The Tracer AdaptiView Main Processor provides the hot
water temperature control mode as standard. The leaving
condenser water temperature is controlled to a hot water
setpoint between 26.7 and 60.0°C (80°F and 140°F). 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
condenser water temperature sensor is an MMR
diagnostic when in hot water temperature control mode.
(It is an informational warning in the normal cooling
mode.)
In the hot water temperature control mode the differential-
to-start and differential-to-stop setpoints are used with
respect to the hot water setpoint instead of with the chilled
water setpoint. The control panel provides a separate
entry at the Tracer AdaptiView to set the hot water
setpoint. Tracer AdaptiView is also able to set the hot water
setpoint. In the hot water mode the external chilled water
setpoint is the external hot water setpoint; that is, a single
analog input is shared at the 1K6-J2-5 to 6 (ground).
An external binary input to select external hot water
control mode is on the EXOP OPTIONAL module 1K8
terminals J2-3 to J2-4 (ground). Tracer AdaptiView also
has a binary input to select chilled water control or hot
water temperature control. There is no additional leaving
hot water temperature cutout; the HPC and condenser
limit provide for high temperature and pressure
protection.
In hot water temperature control the softloading pulldown
rate limit operates as a softloading pullup rate limit. The
setpoint for setting the temperature rate limit is the same
setpoint for normal cooling as it is for hot water
temperature control. The hot water temperature control
feature is not designed to run with HGBP, AFD, free
cooling, or ice building.
The factory set PID tuning values for the leaving water
temperature control are the same settings for both normal
cooling and hot water temperature control.
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