The Tribune Tower, built in 1922-24, is an architectural and historical gem located on Chicago's Magnificent Mile. In 1934, the 32-story building was retrofitted to provide air-conditioning. A 600 ton steam jet refrigeration system supplied chilled water to 387 space air-conditioners - at that time, one of the world's largest air-conditioning installations. In 1948, the steam jet chiller was replaced with two 500 ton electric centrifugals. A third 1,000 ton chiller was added in 1963. G/BA's project entailed replacing these three centrifugal chillers and upgrading the distribution after more than 60 years of service. Cooling energy use was reduced by more than $90,000 in the first year of operation.

• Three electric centrifugal chillers, rated at 500, 500 and 1,000 tons, were installed in 1948 and 1963. All three were replaced with new high efficiency chillers with variable frequency drives (VFDs) rated at 1,150, 850 and 500 tons.
• Chillers use Chicago River water for condenser cooling. The original river water pumps were replaced and converted to variable flow to minimize the use of river water, maximize delta-T and limit discharge water temperatures to no more than 90F.
• The primary-only chilled water distribution loop was converted to variable flow, new pumps were equipped with VFDs, 3-way chilled water control valves were replaced with new 2-way valves.
• Aged electrical service and switch gear serving the chiller plant were replaced.
• The chiller equipment room ventilation was upgraded to comply with ASHRAE Standard 15.