University of Wisconsin-Madison
IN-26: Innovation C

In recent years, UW-Madison has pumped untreated lake water from Lake Mendota to supply certain systems in its heating and cooling plants. Using lake water means that the Charter and Walnut Street Heating & Cooling plants on campus, along with West Campus Cogeneration Facility, do not rely on groundwater for their operations. Lake water presents challenges, however, because it carries biological organisms that can accumulate inside pipes and other pieces of machinery.

For this reason, in 2013 the university began treating lake water with a sand ballast clarifier system, which used bleach, coagulants, sand, and flocculants to remove impurities. The downside of this system was that the waste water was going down the sanitary sewer drain, in order for the bleach to be removed from the water before redistribution into the natural environment.

To address this issue, the Charter Street Heating & Cooling Plant team tried an experiment: they stopped injecting the bleach into the lake water that supplied the closed-loop cooling (CLC) systems and cooling tower. As part of this process, the Charter Street team and UW-Madison’s water treatment vendor, U.S. Water, worked diligently to maximize the Charter and Walnut Street Plants’ performance while minimizing cost and maintenance. After careful testing, they found that residual chlorine was gone from their systems and that no problematic organic buildup was occurring in their machinery.

By making this relatively simple change, the Charter Street plant diverted over 70 million gallons of water from the sanitary sewer drain to the storm sewer between 2016-2017. This water now flows, effectively, from one lake to another: it begins in Lake Mendota, and is discharged into Lake Monona under Department of Natural Resources (DNR) guidelines, a process that mimics the natural flow of water in the Yahara River Watershed. Moreover, avoiding the sanitary sewer drain, and thus the wastewater treatment plant, reduces both energy usage and emissions associated with water treatment.

U.S. Water was so impressed that they gave UW-Madison an award for sustainability, recognizing the reduction in sanitary sewer volume from the plant and an annual savings of $191,970.

Spurred by this success, the Charter Street Heating & Cooling Plant team initiated an additional, innovative upgrade. Each chiller at the plant contains at least 3100 tubes in the evaporator and condenser units, which gradually experience build-up on their inner walls and a corresponding reduction in efficiency and performance. By installing new equipment in a trial chiller that circulates hundreds of small, foam balls through these tubes, the entire system was cleaned at least once per day, reducing costly and time-consuming routine maintenance.

This upgrade has yielded both economic and environmental benefits. In a six-month test of the new cleaning method, the trial chiller at Charter Street saw a $40,000 savings in natural gas. It also gained an equivalent of 400-500 tons of cooling capacity compared with the previous year. Once the foam balls are added to the additional three chillers, the team expects that the plant will save $220,000 in natural gas per year—which directly translates to fewer greenhouse gas emissions.