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Air Cooled Vs. Water Cooled Chillers

Conventional thinking has been that water cooled chillers are more efficient than air cooled chillers. If we only look at compressor costs, this may be true. However, using state-of-the-art technology with centrifugal compressors and variable speed control, air-cooled chillers are often the better choice. When taking a deeper look into air cooled chillers versus water cooled chillers, it is recommended to consider the operating costs associated with each chiller system.

Centrifugal Compressor

air cooled chiller vs water cooled comparison costIt is important to look at the total operating costs involved with the chillers, not just the compressor costs when evaluating the differences and advantages between air and water cooled chillers. As the graphic indicates, cooling tower operating costs should be added to the operating costs of a water cooled chiller. A cooling tower system's costs include the tower fan, water and sewer costs, chemical costs and pumping costs. In process applications, tower systems generally have process pumps and recirculation pumps which can add a significant cost. The illustration below compares the operating cost of an air cooled variable speed centrifugal chiller versus a water cooled screw chiller. This comparison is based upon a 140 ton load, Chicago weather data, $.07/kwh electrical costs, $5.00/1000 gallon water and sewer costs and 6,000 hrs/year operation.

Because the air cooled chiller uses floating head pressure control, the compressor energy costs are actually less than the water cooled chiller's compressor costs-a $4,757 difference ($20,585-$15,585). Adding the tower system's operating cost of $17,429 results in a $22,186/year operating cost savings. A more efficient variable speed water cooled centrifugal chiller reduces the cost difference to $16,725-still a significant annual cost penalty.

 air vs water cooled chiller cost breakdown

Centrifugal Compressor

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