Features and Benefits |
Unit Options - Free Cooling |
Unit Options — Free Cooling
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.
Benefits
Operating Cost Savings
Up to 45 percent of chiller capacity
during fall, winter and spring without compressor motor operation.
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. Reliability
Two simple valves are the only moving parts. Single-Source
Responsibility Free cooling is Trane engineered,
manufactured and installed.
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)
T
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.
Temperature and humidity control
requirements are important considerations
when evaluating the use of CenTraVac free cooling. It
is often possible to reduce total energy costs through the use of a free cooling chiller. Low temperature outside air (from the
outside air economizer) often requires a large amount
of energy for humidification purposes. Free cooling
operation helps to reduce these humidification costs on many applications.
It is important to note that those
applications which require extremely precise humidity control typically cannot
tolerate warmer than design chilled water temperatures.
Therefore, since free cooling chillers normally deliver warmer than design chilled water temperatures, free cooling operation is
usually not applicable with systems which require
precise humidity control.
Also, free cooling is generally not
used in conjunction with heat recovery systems, since mechanical cooling must
be used to recover heat that will be used elsewhere in
the building for simultaneous heating. |
