Consulting-Specifying Engineer: Turning wasted heat into savings

The building sits on a large medical campus in the Milwaukee area that shares a central energy plant, which supplies chilled water and steam to more than 25 buildings. That shared system works well for most of the building's needs, but it wasn't a good fit for everything.

The challenge came from the building's research spaces. Walk-in coolers, freezer rooms and equipment rooms need steady and precise cooling all year, and the campus plant intentionally sends out slightly warmer water in cold weather to save energy. At the same time, the labs require large amounts of fresh air for safety, which means a lot of energy goes into heating that air back up. The college's safety team also ruled out common energy recovery equipment that carries even a small risk of mixing exhaust air with fresh air.

The design team's answer was a set of five small chillers dedicated to those critical spaces. What makes the system unusual is what happens to the heat those chillers produce. Instead of venting it outdoors through a cooling tower (the building doesn't have one), the system sends that heat into the building's own heating loops, reducing how much steam the college has to buy. It reuses more than 75% of that waste heat each year and saves about $52,000 annually, paying back its $870,000 cost in roughly 16 to 17 years, well within the life of the building.