Free cooling is a type of process cooling system design that takes advantage of ambient temperatures to reduce or even eliminate chiller operation. Chillers consume large amounts of energy; so, reducing a chiller’s operating hours per year can result in significant bottom line savings for your company.  In this article, we will review a typical free cooling system design, some of the considerations for your system, and finally, how these considerations impact your system’s ability to capitalize on the free cooling operation.

“Evaporative cooling capacity for the district system is provided by a six-cell, open-loop cooling tower capable of 6,000 tons,” said Reid Olsen, USU Central Energy Plant Manager, who has been at the university for 26 years. “This tower serves the condensers of the water-cooled chillers at the heart of the district cooling system. There are four chillers in all, two of which are rated for 1,800 tons each, and the other two are 900 tons apiece. The cooling towers reject heat from the condenser water loop via evaporative cooling, allowing the chillers to supply chilled water to the campus cooling loop.”
An airside economizer is typically used on a packaged rooftop or tied to an indoor AHU, allowing filtered outside air into the space when outdoor temperatures drop below 55°F (12 °C) (the common supply air temperature of indoor spaces) thus alleviating the need for the refrigeration cycle to be running. Interior space is being cooled yet the refrigeration system is not running, hence the name Free Cooling.
Process cooling system applications experiencing constant production loads generating high process fluid temperatures are particularly good candidates to take advantage of low ambient temperatures. Low ambient temperatures can be used as a “free” energy source, replacing the electricity required to run refrigeration compressors, in what is known as a free-cooling chiller system.
Heat recovery opportunities have resulted in the largest amount of savings of our common projects our industrial energy management teams have implemented.  It is not the easiest type of project to implement but the amount of savings and the reduction of emissions makes this project very worthwhile.