The energy plant to the south of the cache is one of five plants in downtown Chicago that form the World’s Largest Interconnected District Cooling System, currently serving about 100 buildings in downtown Chicago.
District energy is an alternative to the installation and operation of on-site chilling plants used in the air conditioning of large condominium, commercial and industrial buildings.
There are 5 district energy plants in the downtown Chicago area that contain many chillers. The chillers use refrigerants to chill distribution system water. They can also freeze some distribution water for "thermal storage" and then melt it for cooling when needed.
The distribution system water is then sent via a system of underground pipes to heat exchangers at customer facilities. The distribution system water does not mix with building air-conditioning water. Instead the thermal energy is transferred via these heat exchangers, which allow the transfer of cooling energy from the thermal distribution water to the building's cooling water system for use in the distribution of cool air throughout the building.
The distribution system water then returns to the plants for re-chilling through the same continuous process.
Cool, huh. :)
Location tweaked using Google Maps aerial view.