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).
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.
Free Cooling Operation Schematic
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).
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.
