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CTV-PRC007-EN18
Benefits
The Trane patented free cooling
accessory for Trane CenTraVac
™
chillers
adapts the basic chiller so it may
function as a simple heat exchanger
using refrigerant as the working fluid.
When condenser water is available at
temperatures lower than the desired
chilled liquid temperature, free cooling
can provide up to 45 percent of nominal
chiller capacity without operation of the
compressor. This feature may result in
substantial energy cost savings on many
installations.
The suitability of free cooling for any
particular installation depends upon a
number of factors. The availability of
low temperature condensing water, the
quality of the outside air, the type of
airside system, the temperature and
humidity control requirements, and the
cost of electricity all have a direct impact
on the decision to use a free cooling
chiller.
The use of CenTraVac free cooling
depends on the availability of cold
condenser water from a cooling tower,
river, lake, or pond. As a general rule of
thumb, locations which have a
substantial number of days with
ambient temperatures below 45°F wet
bulb or more than 4000 degree-days per
year are well suited to free cooling
operation. A cooling tower usually must
be winterized for off-season operation
and the minimum sump temperature is
limited by some cooling tower
manufacturers. Cooling tower
manufacturers should be consulted for
recommendations on low temperature
operation. With river, lake or pond
supply, condenser water temperatures
down to freezing levels are possible.
Areas which have badly fouled air may
be more conducive to free cooling
operation than the use of an outside air
economizer.
Airside systems which both heat and
cool the air can often effectively use a
free cooling chiller. Dual-duct, multizone,
and reheat systems fall into this general
category. As the outside temperature
begins to fall, the cool outside air
satisfies the cooling requirements
(through an outside air economizer). As
the outdoor air temperature becomes
very low, the outdoor air may need to be
heated in order to maintain the design
supply air temperature when it is mixed
with return air. This “heating penalty”
can be eliminated by using CenTraVac
free cooling. Warm chilled water
temperatures provided by the free
cooling chiller would allow a warmer air
temperature off the chilled water coils,
eliminating the heating energy required
by using only an outside air economizer.
With today’s high cost electricity in most
areas of the country, this heating penalty
can be very significant.
Free Cooling Allows
Reduced Operating Costs
Consider a CenTraVac
™
chiller option that
can provide up to 45 percent of the
nominal chiller capacity — without
operating the compressor. Think of the
significant energy and cost savings
possible in many applications. This
option is available on all Trane chillers,
factory installed.
Free cooling operation is based on the
principle that refrigerant migrates to the
area of lowest temperature. When
condenser water is available at
temperatures lower than the required
leaving chilled water temperature
(typically 50 to 55°F), the unit control
panel starts the free cooling cycle
automatically.
When the free cooling cycle can no
longer provide sufficient capacity to meet
cooling requirements, mechanical
cooling is restarted automatically by the
unit control panel.
For example, a building with a high
internal cooling load is located in a
climate with cold winters. It is possible to
cool the building exclusively with free
cooling three to six months of the year!
Free cooling payback can easily be less
than a year.
Free cooling is completely factory
installed and requires no more floor
space or piping than the standard
CenTraVac chiller (unlike plate frame heat
exchangers).
Free Cooling Operation Schematic
Free Cooling
Unit
Options
Reliability
Two simple valves are the only moving
parts.
Single-Source Responsibility
Free cooling is Trane engineered,
manufactured and installed.
Ease of Operation
Changeover on free cooling by single
switch control.
Ease of Installation
Completely factory-installed and leak-
tested components. All valve operators
and controls are factory wired.
Application
Modern buildings often require some
form of year-round cooling to handle
interior zones, solar loads, or computer
loads. As the outside air temperature
decreases below the inside air design
temperature, it is often possible to use
an outside air economizer to satisfy the
cooling requirements. There are a
number of instances, however, where
CenTraVac free cooling offers a number
of advantages over the use of an outside
air economizer. It is possible for the free
cooling chiller to satisfy the cooling load
for many hours, days, or months during
the fall, winter, or spring seasons without
operation of the compressor motor. This
method of satisfying the cooling
requirement can result in significant total
energy savings over other types of
systems. The savings available are most
easily determined through the use of a
computer energy analysis and economic
program, such as TRACE
™
(Trane Air
Conditioning and Economics).