Free Cooling Cycle; Hot Water Control - Trane CVHH Installation, Operation And Maintenance Manual

Start-up and Shut-dow n

Free Cooling Cycle

Based on the principle that refrigerant m igrates to the
coldest area in the system , the free cooling option adapts
the basic chiller to function as a sim ple heat exchanger.
How ever, it does not provide control of the leaving chilled
water tem perature.
If condenser water is available at a tem perature low er than
the required leaving chilled water tem perature, the
operator interface m ust rem ain in AUTO and the operator
starts the free cooling cycle by enabling the Free cooling
m ode in the Tracer AdaptiView Feature Settings group of
the operator interface, or by m eans of a BAS request. The
follow ing com ponents m ust be factory-installed or field-
installed to equip the unit for free cooling operation:
• a refrigerant gas line, and electrically-actuated shutoff
valve, betw een the evaporator and condenser, and
• a valved liquid return line, and electrically-actuated
shutoff valve, betw een the condenser sum p and the
evaporator.
When the chiller is changed over to the free cooling m ode,
the com pressor w ill shut dow n if running, the shutoff
valves in the liquid and gas lines open; unit control logic
prevents the com pressor from energizing during free
cooling. Since the tem perature and pressure of the
refrigerant in the evaporator are higher than in the
condenser (i.e., because of the difference in water
tem perature), the refrigerant in the evaporator vaporizes
and travels to the condenser, cooling tow er water causes
the refrigerant to condense on the condenser tubes, and
flow (again, by gravity) back to the evaporator.
This com pulsory refrigerant cycle is sustained as long as
a tem perature differential exists betw een condenser and
evaporator water. The actual cooling capacity provided by
the free cooling cycle is determ ined by the difference
betw een these tem peratures w hich, in turn, determ ines
the rate of refrigerant flow betw een the evaporator and
condenser shells.
If the system load exceeds the available free cooling
capacity, the operator m ust m anually initiate changeover
to the m echanical cooling m ode by disabling the free
cooling m ode of operation. The gas and liquid line valves
then close and com pressor operation begins (see
Figure 42, p. 76, beginning at Auto m ode). Refrigerant gas
is draw n out of the evaporator by the com pressor, w here
it is then com pressed and discharged to the condenser.

Hot Water Control

Occasionally CTV chillers are selected to provide heating
as a prim ary m ission. With hot water tem perature 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
tem perature and the chiller capacity is m odulated to
m aintain the hot water setpoint. Heating is the prim ary
m ission and cooling is a waste product or is a secondary
m ission. This type of operation requires an endless source
80
of evaporator load (heat), such as w ell or lake water. The
chiller has only one condenser.
N ot e: Hot water tem perature control m ode does not
convert the chiller to a heat pum p. Heat pum p
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 im practical for centrifugal chillers as it w ould be
m uch easier to sw itch over the water side.
This is NOT heat recovery. Although this feature could be
used to recover heat in som e form , a heat recovery unit has
a second heat exchanger on the condenser side.
The Tracer AdaptiView M ain Processor provides the hot
water tem perature control m ode as standard. The leaving
condenser water tem perature is controlled to a hot water
setpoint betw een 26.7 and 60.0° C (80° F and 140° F). The
leaving evaporator water tem perature is left to drift to
satisfy the heating load of the condenser. In this
application the evaporator is norm ally piped into a lake,
w ell, or other source of constant tem perature water for the
purpose of extracting heat. In hot water tem perature
control m ode all the lim it m odes and diagnostics operate
as in norm al cooling w ith one exception; the leaving
condenser water tem perature sensor is an M M R
diagnostic w hen in hot water tem perature control m ode.
(It is an inform ational warning in the norm al cooling
m ode.)
In the hot water tem perature control m ode the differential-
to-start and differential-to-stop setpoints are used w ith
respect to the hot water setpoint instead of w ith 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 m ode 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 m ode is on the EXOP OPTIONAL m odule 1K8
term inals J2-3 to J2-4 (ground). Tracer AdaptiView also
has a binary input to select chilled water control or hot
water tem perature control. There is no additional leaving
hot water tem perature cutout; the HPC and condenser
lim it provide for high tem perature and pressure
protection.
In hot water tem perature control the softloading pulldow n
rate lim it operates as a softloading pullup rate lim it. The
setpoint for setting the tem perature rate lim it is the sam e
setpoint for norm al cooling as it is for hot water
tem perature control. The hot water tem perature control
feature is not designed to run w ith HGBP , AFD, free
cooling, or ice building.
The factory set PID tuning values for the leaving water
tem perature control are the sam e settings for both norm al
cooling and hot water tem perature control.
CVHH-SVX001A-EN