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.